What do ice molecules look like? Crystal lattice of ice and water
Candidate technical sciences V. BELYANIN, Leading Researcher, RRC "Kurchatov Institute", E. ROMANOVA, student of MADI (GTU).
Researchers find the ratios of the golden ratio in the morphological structure of plants, birds, animals, and humans. The patterns of the golden ratio are also found in the organization of inanimate nature. In this article, based on the analysis of the water molecule in various states of aggregation, a hypothesis is put forward that its structure in the state of melt water practically corresponds to the triangle of the golden ratio.
Science and life // Illustrations
The heat capacity of water reaches its minimum value at a temperature of about 37 O WITH.
Science and life // Illustrations
ill. 1. The density of water with decreasing temperature first increases, reaches a maximum at 4 O C and starts to decrease.
Science and life // Illustrations
At the moment of melting, the volume of lead instantly increases from 1 to 1.003, and the volume of water abruptly decreases from 1.1 to 1.0.
Science and life // Illustrations
Water has abnormal high temperatures boiling and freezing compared to other triatomic hydrogen compounds.
Science and life // Illustrations
In liquid water molecules H 2 O can combine into complex formations - clusters that resemble ice in structure.
Science and life // Illustrations
Schematic representation of a water molecule on a plane.
The division of the segment in the extreme and average ratio, or the golden ratio. The segment is divided into two parts so that CB:AC = AC:AB.
"Golden Triangle". Its aspect ratio is OA:AB = OB:AB ≈ 0.618,
Science and life // Illustrations
Science and life // Illustrations
Science and life // Illustrations
Table 1.
Table 2.
Water was given the magical power to become the juice of life on Earth.
Leonardo da Vinci
Water is one of the most unique and mysterious substances on Earth. The nature of this substance is not yet fully understood. Outwardly, water seems quite simple, and therefore for a long time it was considered an indivisible element. Only in 1766 G. Cavendish (England) and then in 1783 A. Lavoisier (France) showed that water is not a simple chemical element, but a combination of hydrogen and oxygen in a certain proportion. After this discovery, the chemical element, denoted as H, received the name "hydrogen" (Hydrogen - from the Greek hydro genes), which can be interpreted as "generating water."
Further studies have shown that behind the unpretentious chemical formula H 2 O lies a substance with a unique structure and no less unique properties. Researchers who have been trying for more than two centuries to uncover the secrets of water have often come to a standstill. Even now, scientists understand that water remains a difficult object for research, its properties are still not always fully predictable.
Mysterious water magic. Why is liquid water unusual properties? The traditional answer may be as follows: due to the properties of oxygen and hydrogen atoms, due to their structural arrangement in the molecule, due to a certain behavior of electrons in the molecule, etc.
So what are the mysterious, unusual properties of liquid water familiar to everyone? First of all, in the fact that almost all properties of water are anomalous, and many of them do not obey the logic of those laws of physics that govern other substances. Let us briefly mention those of them that determine the existence of life on Earth.
First, about three features of the thermal properties of water.
The first feature: water is the only substance on Earth (except mercury) for which the dependence of specific heat on temperature has a minimum.
Due to the fact that the specific heat capacity of water has a minimum of about 37 o C, the normal temperature of the human body, which consists of two-thirds of water, is in the temperature range of 36-38 o C ( internal organs have a higher temperature than outdoor).
The second feature: the heat capacity of water is abnormally high. To heat a certain amount of it by one degree, it is necessary to expend more energy than when heating other liquids - at least twice as compared to simple substances. This results in the unique ability of water to retain heat. The vast majority of other substances do not have this property. This exceptional feature of water contributes to the fact that a person's normal body temperature is maintained at the same level both on a hot day and a cool night.
Thus, water plays a leading role in the processes of regulating human heat exchange and allows him to maintain a comfortable state with a minimum of energy costs. At normal body temperature, a person is in the most favorable energy state.
The temperature of other warm-blooded mammals (32-39 o C) also correlates well with the temperature of the minimum specific heat of water.
The third feature: water has a high specific heat of fusion, that is, it is very difficult to freeze water, and melt ice. Thanks to this, the climate on Earth as a whole is quite stable and mild.
All three features of the thermal properties of water allow a person to optimally exist in a favorable environment.
There are features in the behavior of the volume of water. The density of most substances - liquids, crystals and gases - decreases when heated and increases when cooled, up to the process of crystallization or condensation. The density of water when cooled from 100 to 4 o C (more precisely, to 3.98 o C) increases, as in the vast majority of liquids. However, having reached its maximum value at a temperature of 4 ° C, the density begins to decrease with further cooling of the water. In other words, the maximum density of water occurs at a temperature of 4°C (one of the unique anomalies of water), and not at a freezing temperature of 0°C.
The freezing of water is accompanied by an abrupt (!) decrease in density by more than 8%, while in most other substances the process of crystallization is accompanied by an increase in density. In this regard, ice (solid water) occupies a larger volume than liquid water and stays on its surface.
Such an unusual behavior of the density of water is extremely important for sustaining life on Earth.
Covering the water from above, ice plays in nature the role of a kind of floating blanket that protects rivers and reservoirs from further freezing and keeps the underwater world alive. If the density of water increased when freezing, ice would be heavier than water and begin to sink, which would lead to the death of all living beings in rivers, lakes and oceans, which would freeze entirely, turning into blocks of ice, and the Earth would become an icy desert, which is inevitable would lead to the death of all living things.
Let's note some more features of water.
Externally, water is mobile and pliable, and it can be enclosed in any vessel. However, penetrating into the cracks of rocks and expanding when freezing, water splits rocks of any hardness, which gradually disintegrate into smaller and smaller particles. This is how the return of petrified rocks to the life cycle begins: in the fields, the freezing of the surface layers of the earth from its organic components helps to form fertile soil.
The process of incorporating solid substances into the great cycle of living nature is accelerated by the miraculous property of water to dissolve them. Water with dissolved components of solids becomes a nutrient medium and a supplier of trace elements necessary for the life of plants, animals and humans.
Water, more than other liquids, exhibits the properties of a universal solvent. Given enough time, it can dissolve almost any solid. It is precisely because of the unique dissolving power of water that no one has yet been able to obtain chemically pure water - it always contains the dissolved material of the vessel. Water is absolutely essential for all key human life support systems. It is contained in human blood (79%) and contributes to the transfer of thousands of substances necessary for life through the circulatory system in a dissolved state. Water is contained in lymph (96%), which carries nutrients from the intestine to the tissues of a living organism (see Table 1).
The listed properties and the special role of water in ensuring life on Earth cannot leave indifferent any inquisitive mind, even if he believes in happy accidents. "The beginning of everything is water," Thales from Miletus rightly noted in the 6th century BC.
liquid miracle. Let's stop listing the strange, but vital properties of water, which can be collected from a dozen more, and turn our attention to the secrets of the unusual structure of its molecule. It is the analysis of the structure of the water molecule that makes it possible to understand its exclusivity in animate and inanimate nature. So the road to truth passes through the structure of a single water molecule.
First of all, we note that the water molecule is the smallest among similar triatomic molecules (in relation to homologues, that is, hydrogen compounds such as H 2 S, H 2 Se, H 2 Te, with the properties of which the properties of water are traditionally compared). Such molecules under normal conditions form gases, and water molecules form liquids. Why?
A chaotic community of gaseous water molecules during condensation, that is, during the formation of a liquid phase, forms a liquid substance of amazing complexity. This is primarily due to the fact that water molecules have a unique property to combine into clusters (groups) (H 2 O) x. A cluster is usually understood as a group of atoms or molecules united by physical interaction into a single ensemble, but retaining individual behavior within it. The possibilities of direct observation of clusters are limited, and therefore experimenters compensate for instrumental shortcomings with intuition and theoretical constructions.
At room temperature degree of association X for water is, according to modern data, from 3 to 6. This means that the formula of water is not just H 2 O, but the average between H 6 O 3 and H 12 O 6. In other words, water is a complex liquid "composed" of repeating groups containing three to six single molecules. As a result, water has anomalous freezing and boiling points compared to homologues. If water obeyed general rules, it had to freeze at a temperature of about -100 o C and boil at a temperature of about +10 o C.
If water during evaporation remained in the form of H 6 O 3, H 8 O 4 or H 12 O 6, then water vapor would be much heavier than air, in which nitrogen and oxygen molecules dominate. In this case, the surface of the entire Earth would be covered with an eternal layer of fog. It is almost impossible to imagine life on such a planet.
People are very lucky: water clusters break up during evaporation, and water turns into almost a simple gas with the chemical formula H 2 O (discovered in Lately in a pair, an insignificant amount of H 4 O 2 dimers does not make a difference). The density of gaseous water is less than the density of air, and therefore water is able to saturate the earth's atmosphere with its molecules, creating weather conditions that are comfortable for humans.
There are no other substances on Earth that are endowed with the ability to be a liquid at the temperatures of human existence and at the same time form a gas that is not only lighter than air, but also capable of returning to its surface in the form of precipitation.
Amazing geometry. So, what is the smallest among the triatomic molecules? The water molecule has a symmetrical V-shape, since two small hydrogen atoms are located on the same side of a relatively large oxygen atom. This greatly distinguishes the water molecule from linear molecules, such as H 2 Be, in which all atoms are arranged in a chain. It is this strange arrangement of atoms in the water molecule that allows it to have many unusual properties.
If we carefully consider the geometric parameters of the water molecule, then a certain harmony is found in it. To see it, let's build an isosceles triangle H-O-H with protons at the base and oxygen at the top. Such a triangle schematically copies the structure of a water molecule, the projection of which onto a plane is conventionally shown in the figure.
The lengths of the sides of this triangle and the bond angle between the two O-H bonds change with the change in the state of aggregation of water. We present these parameters (see Table 2).
Let us comment on the data characterizing the various states of water.
The parameters of the water molecule in the vapor state were obtained from the processing of its absorption spectra. The results have been repeatedly refined, but the bond lengths and the bond angle in the water molecule in the vapor state are essentially correct.
The crystal structure of ice at normal pressure rather loose with a bizarre web of bonds between water molecules. Schematically, the crystal lattice of ordinary ice can be built from oxygen atoms, each of which participates with neighboring atoms in four hydrogen bonds, directed approximately to the vertices of a regular tetrahedron.
Recall that a hydrogen bond is a bond between atoms in one molecule or between neighboring molecules, which is carried out through a hydrogen atom. The hydrogen bond plays an extremely important role in the structure of not only water, but also most biological molecules - carbohydrates, proteins, nucleic acids, etc.
If crystalline ice is well ordered in terms of oxygen, then the same cannot be said about hydrogen: a strong disorder is observed in the arrangement of hydrogen ions (protons). Their position is not clearly defined, and therefore the ice can be considered disordered in terms of hydrogen.
Ice has many amazing features, of which we note two.
First, it is always very pure chemically. There are practically no impurities in the structure of ice: when freezing, they are displaced into the liquid. That is why snowflakes are always white, and ice floes on the surface of a dirty puddle are almost transparent. Generally speaking, any growing crystal tends to create an ideal crystal lattice and displaces foreign matter. But on a planetary scale, it is the wonderful phenomenon of freezing and thawing of water that plays the role of a gigantic cleansing process - water on Earth constantly cleans itself.
Secondly, ice and especially snow are very reflective. Thanks to this, solar radiation does not cause noticeable heating of the polar regions, and, as a result, our planet is spared from seasonal floods and rising sea levels.
Experimental determination of the parameters of a single water molecule in the liquid phase still encounters insurmountable difficulties, since liquid water is a mixture of structural elements, that is, various clusters that are in dynamic equilibrium with each other. There is still no complete clarity regarding their interactions, and it is impossible to separate such a mixture into separate components: the "simple" liquid H 2 O is in no hurry to reveal its inner secrets.
Let's go back to the picture where in general terms the structure of the water molecule is shown. It has symmetry, which plays a major role in attempts to comprehensively explain the physical world, and asymmetry, which gives this molecule the possibility of movement and connection with the golden ratio. Therefore, we briefly recall what is called the golden ratio in mathematics.
golden ratio . This concept arises when solving the geometric problem of being on a segment AB such a point WITH to satisfy the relation SW:AC = AC:AB.
The solution of this problem leads to the relation SW:AC= (-1+√5)/2, which is called the golden ratio, and the corresponding geometric division of the segment AB dot WITH called the golden ratio. If we take the entire segment as unity, then AC= 0.618033… and SW = 0,381966....
Time has shown that the golden ratio embodies the perfect and harmonious relationship of two quantities. In geometric interpretation, it leads to a proportionate and attractive relationship between two unequal segments.
Researchers of the golden ratio from ancient times to the present day have always admired and continue to admire its properties, which are manifested in the structure of various elements of the physical and biological world. The golden ratio is found wherever the principles of harmony are observed.
What unites the golden ratio with the water molecule? To answer this question, consider a two-dimensional image of the golden ratio in the form of a triangle.
In the golden triangle OA:AB = OV:AB approximately equal to 0.618, angle α = 108.0 o. For ice, the length ratio O-H connections to H-H is 0.100: 0.163 \u003d 0.613 and the angle α \u003d 109.5 o, for steam - 0.631 and 104.5 o, respectively. It is simply impossible not to recognize the prototype of the structure of the water molecule in the golden triangle! It is surprising that until now so little attention has been paid to the possibility of such an interpretation of its structure.
Indeed, placing in a triangle AOB to points A And IN hydrogen atoms, and to the point O - an oxygen atom, we obtain, in the first approximation, a molecule of liquid water, constructed on the basis of the golden ratio. Such elegance of the molecule captivates and delights. So the role of the water molecule in nature and life cannot be properly assessed without taking into account the beauty of its form.
Exceptional harmony. Let us make sure that the liquid water molecule is the only triatomic substance that has proportions characteristic of the golden ratio.
In triatomic homologue molecules close in chemical composition to a water molecule (H 2 S, H 2 Se and H 2 Te), the bond angle is approximately 90 o. For example, an H 2 S molecule has the following geometric parameters:
S-H bond length, nm ............................. 0.1345
length connections H-H, nm...................... 0.1938
bond angle Н-S-Н, deg .............. 92.2
Length ratio S-H bonds to H-H is 0.694, which is far from the golden ratio. Quantum-chemical calculations show that if water were similar to its related substances, then the bond angle of its molecule should be approximately the same as that of H 2 S, or more by a maximum of 5 o.
But water, as it turns out, does not like similarities, it is always the hero of another novel. If the valence angle of water were of the order of 90-95 o, the golden ratio would have to be forgotten and water would be in the same community with other hydrogen compounds.
But water is unique, its molecule has almost verified aesthetic qualities, and therefore its properties must sometimes be interpreted, going beyond the traditional scientific paradigm. And then some of the mysteries of water can be explained by such an "unscientific" concept as harmony.
One can object to the above reasoning: experimental measurements of the geometric parameters of the water molecule have a certain error, and therefore the golden ratio may not be strictly fulfilled. But even if an even greater error is introduced into the experimental measurements, the water molecule will still remain the only one of the triatomic substances that has practically "golden" harmonious proportions.
In this regard, let's pay attention to the mystery of melt water, which, according to the widespread opinion, has a physiological effect different from ordinary water.
Amazing melt water. It is born when ice melts and remains at 0 o C until all the ice has melted. The specificity of intermolecular interactions, characteristic of the structure of ice, is also preserved in melt water, since only 15% of all hydrogen bonds are destroyed during the melting of the crystal. Therefore, the bond inherent in ice between each water molecule and its four neighbors ("short range order") is not violated to a large extent, although the oxygen framework lattice is more blurred.
Thus, melt water differs from ordinary water in the abundance of multimolecular clusters, in which loose ice-like structures remain for some time. After all the ice has melted, the temperature of the water rises and the hydrogen bonds within the clusters no longer resist the increasing thermal vibrations of the atoms. The sizes of the clusters change, and therefore the properties of melt water begin to change: the dielectric constant reaches its equilibrium state after 15-20 minutes, the viscosity - after 3-6 days. The biological activity of melt water decreases, according to some data, approximately in 12-16 hours, according to others - in a day.
So, physicochemical characteristics melt water spontaneously change in time, approaching the properties of ordinary water: it gradually, as it were, "forgets" that until recently it was ice.
Ice and vapor are different states of aggregation of water, and therefore it is logical to assume that in the liquid intermediate phase the bond angle of an individual water molecule lies in the range between the values in the solid phase and in vapor. In an ice crystal, the bond angle of a water molecule is close to 109.5 o. When ice melts, intermolecular hydrogen bonds weaken, distance H-H decreases slightly, the bond angle decreases. When liquid water is heated, the cluster structure is disordered, and this angle continues to decrease. In the vapor state, the bond angle of the water molecule is already 104.5 o.
This means that for ordinary liquid water, the bond angle may well have some average value between 109.5 and 104.5 o, that is, approximately 107.0 o. But since melt water is close to ice in its internal structure, the bond angle of its molecule should be closer to 109.5 o, most likely, about 108.0 o.
The above can be formulated as a hypothesis: due to the fact that melt water is much more structured than ordinary water, its molecule with a high degree of probability has a structure that is as close as possible to the harmonious triangle of the golden ratio with a bond angle close to 108 o, and with a ratio of bond lengths of approximately 0.618-0.619.
The authors have no experimental confirmation of this hypothesis, just as there is no theory of its justification. There is only a conjecture expressed in these pages, which can, of course, be disputed.
Mysterious power of melt water. From time immemorial, people have known the amazing properties of melt water. It has long been noted that the vegetation of alpine meadows is always more luxuriant near melting springs, and life blooms rapidly near the edge of melting ice in the Arctic seas. Watering with melt water increases crop yields, accelerates seed germination. With the use of melt water, the weight gain in animal husbandry steadily increases, the development of chickens accelerates. It is known with what greed animals drink melted water in spring, and birds literally bathe in the first puddles of melted snow.
Melt water, unlike ordinary water, is very similar in structure to the liquid contained in the cells of plant and living organisms. That is why the "ice" structure of melt water, in which the molecules are combined into openwork clusters, is more suitable for a person. This unique property of melt water contributes to its easy absorption by the body, it is biologically active. That is why vegetables and fruits are so useful - they deliver water with a similar structure to the body.
When drinking melt water, the body is nourished by the most harmonious of all substances on Earth. It improves metabolism and enhances blood circulation, reduces the amount of cholesterol in the blood and soothes pain in the heart, increases the adaptive capacity of the body and helps prolong life. A sip of the purest melt water tones better than pasteurized juice, it has a charge of energy, cheerfulness and lightness.
One of the authors of this work constantly drinks melted water with floating ice floes and believes that this is why he has never caught a cold in three years. Melt water refreshes and rejuvenates the skin, which no longer needs creams and lotions.
The theoretical study of the properties of melt water is still at the level of hypotheses. There is no generally accepted opinion about the reasons that cause unusual effects when using it. There are certain problems with the evidence side of the biological activity of melt water. Research in this direction sometimes causes heated discussions. The complexity of the problem, the lack of clarity - all this should not scare away, but attract and contribute to the emergence of new ideas, hypotheses, theories. Such is the often thorny path of the development of science.
We emphasize that the above hypothesis does not claim to decipher the riddle of melt water. It only allows you to go beyond traditional thinking and look at the mutual love of life and water from an unusual side - from the side of harmony and beauty, from the side of the special properties of melt water, which add features to its elegant molecule that other molecules do not have.
LITERATURE
Auerbach F. Seven anomalies of water. - St. Petersburg, 1919.
Gabuda S.P. Bound water. Facts and hypotheses. - Novosibirsk: Science, 1982.
Zatsepina GN Physical properties and structure of water. - M.: MGU, 1998.
Sinyukov VV Water known and unknown. - M.: Knowledge, 1987.
Belyanin V.S., Romanova E. Golden proportion. New look // Science and life, 2003, No. 6.
Water: structure, state, solvation. Achievements recent years. - M.: Nauka, 2003.
Captions for illustrations
ill. 1. The density of ice is almost 10% less than that of water, and the specific volume is by the same amount greater. Therefore, ice floats, and water, freezing in the cracks of rocks, splits them.
Water properties
Why is water water?
Among the boundless multitude of substances, water, with its physical and chemical properties, occupies a very special, exceptional place. And this must be taken literally.
Almost all physical and chemical properties of water are an exception in nature. She really is the most amazing substance in the world. Water is amazing not only by the variety of isotopic forms of the molecule, and not only by the hopes that are associated with it as an inexhaustible source of energy for the future. In addition, it is amazing and its - the most common properties.
How is a water molecule built?
How one molecule of water is built is now known very precisely. It's built like this.
The mutual arrangement of the nuclei of hydrogen and oxygen atoms and the distance between them have been well studied and measured. It turned out that the water molecule is non-linear. Together with the electron shells of atoms, a water molecule, if you look at it "from the side", could be depicted like this:
i.e., geometrically, the mutual arrangement of charges in a molecule can be depicted as a simple tetrahedron. All water molecules with any isotopic composition are built in exactly the same way.
How many water molecules are in the ocean?
One. And this answer is not entirely a joke. Of course, everyone can, after looking in the reference book and finding out how much water is in the World Ocean, it is easy to calculate how many H2O molecules it contains. But this answer is not entirely correct. Water is a special substance. Due to the peculiar structure, individual molecules interact with each other. A special chemical bond due to the fact that each of the hydrogen atoms of one molecule pulls towards itself the electrons of the oxygen atoms in neighboring molecules. Due to such a hydrogen bond, each water molecule is quite strongly associated with four other neighboring molecules, just as it is shown in the diagram. True, this scheme is too simplified - it is flat, otherwise you cannot depict it in the figure. Let's imagine a slightly more accurate picture. To do this, it must be taken into account that the plane in which the hydrogen bonds are located (they are indicated by a dotted line) in the water molecule is directed perpendicular to the plane of the hydrogen atoms.
All individual H2O molecules in water are bound into a single continuous spatial grid - into one giant molecule. Therefore, the assertion of some scientific physical chemists that the entire ocean is one molecule is quite justified. But this statement should not be taken too literally. Although all water molecules in water are interconnected by hydrogen bonds, they are in the same burden in a very complex mobile equilibrium, retaining the individual properties of single molecules and forming complex aggregates. This idea applies not only to water: a piece of diamond is also one molecule.
How is an ice molecule built?
There are no special ice molecules. Water molecules, due to their remarkable structure, are connected in a piece of ice to each other in such a way that each of them is connected and surrounded by four other molecules. This leads to the formation of a very loose structure of ice, in which a lot of free volume remains. correct crystal structure ice is expressed in the amazing grace of snowflakes and in the beauty of frosty patterns on frozen window panes.
How are water molecules built in water?
Unfortunately this one is very important question not yet studied enough. The structure of molecules in liquid water is very complex. When ice melts, its network structure is partially preserved in the resulting water. The molecules in melt water consist of many simple molecules - aggregates that retain the properties of ice. As the temperature rises, some of them disintegrate, their sizes become smaller.
Mutual attraction leads to the fact that the average size of a complex water molecule in liquid water significantly exceeds the size of a single water molecule. Such an extraordinary molecular structure of water determines its extraordinary physical and chemical properties.
What should be the density of water?
It's a very strange question, isn't it? Remember how the unit of mass was established - one gram. This is the mass of one cubic centimeter water. Hence, there can be no doubt that the density of water should only be as it is. Can you doubt it? Can. Theorists have calculated that if water did not retain a loose, ice-like structure in a liquid state and its molecules were tightly packed, then the density of water would be much higher. At 25°C, it would be equal not to 1.0, but to 1.8 g/cm3.
At what temperature should water boil?
This question is also, of course, strange. After all, water boils at 100 degrees. Everyone knows this. Moreover, everyone knows that it is the boiling point of water at normal atmospheric pressure that is chosen as one of the reference points of the temperature scale, conventionally designated 100 ° C.
However, the question is put differently: at what temperature should water boil? Because the boiling point various substances not random. They depend on the position of the elements that make up their molecules in the periodic system of Mendeleev.
If we compare chemical compounds of various elements with the same composition and belonging to the same group of the periodic table, it is easy to see that the lower the atomic number of the element, the lower its atomic weight, the lower the boiling point of its compounds. According to its chemical composition, water can be called oxygen hydride. H2Te, H2Se and H2S are chemical analogues of water. If we follow their boiling points and compare how the boiling points of hydrides in other groups change periodic system, then you can quite accurately determine the boiling point of any hydride, as well as any other compound. Mendeleev himself in this way was able to predict the properties of chemical compounds of elements not yet discovered.
If we determine the boiling point of oxygen hydride by its position in periodic table, then it turns out that the water should boil at -80 ° C. Therefore, the water boils approximately one hundred and eighty degrees higher , than should boil. The boiling point of water - this is its most common property - turns out to be extraordinary and surprising.
The properties of any chemical compound depend on the nature of its constituent elements and, consequently, on their position in Mendeleev's periodic system of chemical elements. These graphs show the dependences of the boiling and melting points of hydrogen compounds of groups IV and VI of the periodic system. Water is a striking exception. Due to the very small radius of the proton, the forces of interaction between its molecules are so great that it is very difficult to separate them, so water boils and melts at abnormally high temperatures.
Graph A. Normal dependence of the boiling point of hydrides of group IV elements on their position in the periodic table.
Graph B. Among the hydrides of elements of group VI, water has anomalous properties: water should boil at minus 80 - minus 90 ° C, but boils at plus 100 ° C.
Graph B. Normal dependence of the melting point of hydrides of group IV elements on their position in the periodic table.
Graph D. Among the hydrides of elements of group VI, water violates the order: it should melt at minus 100 ° C, and ice icicles melt at 0 ° C.
At what temperature does water freeze?
Isn't the question no less strange than the previous ones? Well, who does not know that water freezes at zero degrees? This is the second reference point of the thermometer. This is the most common property of water. But even in this case, one can ask: at what temperature should water freeze in accordance with its chemical nature? It turns out that oxygen hydride, based on its position in the periodic table, should have solidified at one hundred degrees below zero.
How many liquid states of water are there?
This question is not so easy to answer. Of course, there is also one thing - liquid water familiar to all of us. But water in a liquid state has such extraordinary properties that one has to wonder whether such a simple, seemingly non-provocative
no doubt the answer? Water is the only substance in the world that, after melting, first contracts and then expands as the temperature rises. At about 4°C, water has the highest density. This rare anomaly in the properties of water is explained by the fact that in reality liquid water is a complex solution of a completely extraordinary composition: it is a solution of water in water.
When ice melts, large complex water molecules are first formed. They retain the remains of the loose crystalline structure of ice and are dissolved in ordinary low molecular weight water. Therefore, at first the density of water is low, but as the temperature rises, these large molecules break down, and so the density of water increases until the usual thermal expansion begins to predominate, in which the density of water falls again. If this is true, then several states of water are possible, only no one knows how to separate them. And it is not yet known if it will ever be possible to do this. This extraordinary property of water is of great importance for life. In reservoirs, before the onset of winter, gradually cooling water falls down until the temperature of the entire reservoir reaches 4 ° C. With further cooling, colder water remains on top and all mixing ceases. As a result, an extraordinary situation is created: a thin layer of cold water becomes, as it were, a “warm blanket” for all the inhabitants of the underwater world. At 4°C, they feel clearly good.
What should be easier - water or ice?
Who doesn't know this... After all, ice floats on water. Giant icebergs float in the ocean. Lakes in winter are covered with a floating solid layer of ice. Of course, ice is lighter than water.
But why "of course"? Is it so clear? On the contrary, the volume of all solids increases during melting, and they sink in their own melt. But ice floats on water. This property of water is an anomaly in nature, an exception, and, moreover, an absolutely remarkable exception.
The positive charges in the water molecule are attached to the hydrogen atoms. The negative charges are the valence electrons of oxygen. Their mutual arrangement in a water molecule can be represented as a simple tetrahedron.
Let's try to imagine what the world would look like if water had normal properties and ice, as any normal substance should be, is denser than liquid water. In winter, the denser ice that freezes from above would sink in the water, continuously sinking to the bottom of the reservoir. In summer, the ice, protected by a layer of cold water, could not melt. Gradually, all lakes, ponds, rivers, streams would freeze completely, turning into giant blocks of ice. Finally, the seas would freeze, and beyond them the oceans. Our beautiful blooming green world would become a continuous icy desert, in some places covered with a thin layer of melt water.
How many ices are there?
In nature, on our Earth - one: ordinary ice. Ice is a rock with extraordinary properties. It is solid, but it flows like a liquid, and there are huge icy rivers slowly flowing down from high mountains. Ice is changeable - it constantly disappears and forms again. Ice is unusually strong and durable - for tens of millennia it keeps the body of mammoths, who accidentally died in glacial cracks, without changes. In his laboratories, man managed to discover at least six different, no less amazing ices. They cannot be found in nature. They can only exist at very high pressures. Ordinary ice is preserved up to a pressure of 208 MPa (megapascals), but at this pressure it melts at -22 °C. If the pressure is higher than 208 MPa, dense ice appears - ice-Sh. It is heavier than water and sinks in it. At a lower temperature and higher pressure - up to 300 MPa - even denser ice-P is formed. Pressure above 500 MPa turns ice into ice-V. This ice can be heated to almost 0°C and will not melt even though it is under tremendous pressure. At a pressure of about 2 GPa (gigapascals), ice-VI occurs. This is literally hot ice - it can withstand temperatures of 80°C without melting. Ice-VII, found at a pressure of 3GPa, can perhaps be called red-hot ice. It is the most dense and refractory of known ice. It melts only at 190° above zero.
Ice-VII has an unusually high hardness. This ice can even cause sudden disasters. Huge pressure develops in the bearings in which the shafts of powerful turbines of power plants rotate. If even a little water gets into the grease, it will freeze, despite the fact that the temperature of the bearings is very high. The resulting ice-VII particles, which are of great hardness, will begin to destroy the shaft and bearing and quickly disable them.
Maybe there is ice in space?
As if there is, and at the same time very strange. But it was discovered by scientists on Earth, although such ice cannot exist on our planet. The density of all currently known ices, even at very high pressures, only very slightly exceeds 1 g/cm3. The density of the hexagonal and cubic modification of ice at very low pressures and temperatures, even close to absolute zero, is slightly less than unity. Their density is 0.94 g/cm3.
But it turned out that in a vacuum, at negligible pressures and at temperatures below -170 ° C, under conditions when the formation of ice occurs when it condenses from vapor on a cooled solid surface, absolutely amazing ice arises. Its density is ... 2.3 g / cm3. All hitherto known ices are crystalline, and this new ice appears to be amorphous, characterized by the disordered relative arrangement of individual water molecules; it does not have a definite crystal structure. For this reason, it is sometimes called glass ice. Scientists are sure that this amazing ice should appear in space conditions and play a big role in the physics of planets and comets. The discovery of such superdense ice was unexpected for physicists.
What does it take to melt ice?
Lots of warmth. Much more than to melt this amount of any other substance. Exceptionally large specific heat melting -80 cal (335 J) per gram of ice - this is an anomalous property of water. When water freezes, that amount of heat is released again.
When winter comes, ice forms, snow falls and water gives back heat, warming the earth and air. They resist the cold and soften the transition to a harsh winter. Thanks to this wonderful property of water, autumn and spring exist on our planet.
How much heat is needed to heat water?
So many. More than for heating an equal amount of any other substance. It takes one calorie (4.2 J) to heat a gram of water by one degree. This is more than twice the heat capacity of any chemical compound.
Water is a substance that is further extraordinary in the most ordinary properties for us. Of course, this ability of water has a very great importance not only when cooking dinner in the kitchen. Water is the great distributor of heat throughout the earth. Heated by the Sun under the equator, it carries heat in the oceans in giant streams. sea currents to the distant polar regions, where life is possible only thanks to this amazing feature of water.
Why is sea water salty?
This is perhaps one of the most important consequences of one of the most amazing properties of water. In its molecule, the centers of positive and negative charges are strongly displaced relative to each other. Therefore, water has an exceptionally high, anomalous value of the dielectric constant. For water, e \u003d 80, and for air and vacuum, e \u003d 1. This means that any two opposite charges in water are mutually attracted to each other with a force 80 times less than in air. After all, according to Coulomb's law:
But still, intermolecular bonds in all bodies, which determine the strength of the body, are due to the interaction between the positive charges of atomic nuclei and negative electrons. On the surface of a body immersed in water, the forces acting between molecules or atoms are weakened by almost a hundred times under the influence of water. If the remaining bond strength between molecules becomes insufficient to withstand the action thermal motion, molecules or atoms of the body begin to break away from its surface and pass into the water. The body begins to dissolve, disintegrating either into separate molecules, like sugar in a glass of tea, or into charged particles - ions, like table salt.
It is due to the anomalously high dielectric constant that water is one of the strongest solvents. It is even able to dissolve any rock on earth's surface. Slowly and inevitably, it destroys even granites, leaching easily soluble constituents from them.
Streams, rivers and rivers carry impurities dissolved by water into the ocean. Water from the ocean evaporates and returns to earth again to continue its eternal work again and again. And dissolved salts remain in the seas and oceans.
Do not think that water dissolves and carries into the sea only what is easily soluble, and that sea water contains only ordinary salt that is on the dining table. No, sea water contains almost all the elements that exist in nature. It contains magnesium, and calcium, and sulfur, and bromine, and iodine, and fluorine. In smaller quantities, iron, copper, nickel, tin, uranium, cobalt, even silver and gold are found in it. Over sixty elements have been found by chemists in sea water. Probably, all the rest will be found. Most of all in sea water is table salt. Therefore, the water in the sea is salty.
Can you run on the surface of the water?
Can. To be convinced of this, look at the surface of any pond or lake in the summer. On the water not only walks, but also runs a lot of lively and fast people. If we take into account that the area of \u200b\u200bsupport for the legs of these insects is very small, then it is easy to understand that, despite their small weight, the surface of the water can withstand significant pressure without breaking through.
Can water flow upwards?
Yes maybe. This happens all the time and everywhere. The water itself rises up in the soil, wetting the entire thickness of the earth from the groundwater level. The water itself rises up the capillary vessels of the tree and helps the plant to deliver dissolved nutrients to a great height - from roots deeply hidden in the ground to leaves and fruits. The water itself moves up in the pores of the blotting paper when you have to dry the blot, or in the fabric of the towel when you wipe your face. In very thin tubes - in capillaries - water can rise to a height of up to several meters.
What explains this?
Another remarkable feature of water is its exceptionally high surface tension. Water molecules on its surface experience the action of forces of intermolecular attraction only from one side, and in water this interaction is anomalously large. Therefore, every molecule on its surface is drawn into the liquid. As a result, a force arises that pulls the surface of the liquid. For water, it is especially large: its surface tension is 72 mN / m (millinewton per meter).
Can water remember?
Such a question sounds, admittedly, very unusual, but it is quite serious and very important. It concerns a great physico-chemical problem, which in its most important part has not yet been investigated. This question has only been posed in science, but it has not yet found an answer to it.
The question is whether or not the previous history of water affects its physical and chemical properties and whether it is possible, by studying the properties of water, to find out what happened to it earlier - to make the water itself “remember” and tell us about it. Yes, it is possible, surprising as it may seem. The easiest way to understand this is a simple, but very interesting and unusual example - the memory of ice.
Ice is water. When water evaporates, the isotopic composition of water and steam changes. Light water evaporates, although to a negligible extent, but faster than heavy water.
When natural water evaporates, the composition changes in the isotopic content of not only deuterium, but also heavy oxygen. These changes in the isotopic composition of the vapor are very well studied, and their dependence on temperature is also well studied.
Recently, scientists have staged a remarkable experiment. In the Arctic, in the thickness of a huge glacier in the north of Greenland, a borehole was laid and a giant ice core almost one and a half kilometers long was drilled and extracted. The annual layers of growing ice were clearly visible on it. These layers were subjected to isotopic analysis along the entire length of the core, and the temperatures of the formation of annual ice layers in each section of the core were determined from the relative content of heavy isotopes of hydrogen and oxygen - deuterium and 18O. The date of formation of the annual layer was determined by direct reading. Thus, the climatic situation on Earth was restored over the course of a millennium. Water managed to remember and record all this in the deep layers of the Greenland glacier.
As a result of isotopic analyzes of ice layers, scientists have built a climate change curve on Earth. It turned out that the average temperature in our country is subject to secular fluctuations. It was very cold in the 15th century, at the end of the 17th century. and in early XIX. The hottest years were 1550 and 1930.
Then what is the mystery of the “memory” of water?
The fact is that in recent years, science has gradually accumulated many amazing and completely incomprehensible facts. Some of them are firmly established, others require quantitative reliable confirmation, and all of them are still waiting for their explanation.
For example, no one knows yet what happens to water flowing through a strong magnetic field. Theoretical physicists are absolutely sure that nothing can and does not happen to it, reinforcing their conviction with quite reliable theoretical calculations, from which it follows that after the termination of the magnetic field, the water should instantly return to its previous state and remain as it was . And experience shows that it changes and becomes different.
Is there a big difference? Judge for yourself. From ordinary water in a steam boiler, dissolved salts, escaping, are deposited in a dense and hard, like a stone, layer on the walls of boiler pipes, and from magnetized water (as it is now called in technology) they precipitate in the form of loose sediment suspended in water. It seems like the difference is small. But it depends on the point of view. According to the workers of thermal power plants, this difference is extremely important, since magnetized water ensures the normal and uninterrupted operation of giant power plants: the walls of the pipes of steam boilers do not overgrow, heat transfer is higher, and more electricity is generated. Magnetic water preparation has long been installed at many thermal power plants, but neither engineers nor scientists know how and why it works. In addition, experience has shown that after magnetic treatment of water, the processes of crystallization, dissolution, adsorption are accelerated in it, wetting changes ... however, in all cases, the effects are small and difficult to reproduce.
The action of a magnetic field on water (necessarily fast-flowing) lasts a small fraction of a second, and the water “remembers” this for tens of hours. Why is unknown. In this respect, practice is far ahead of science. After all, it is not known further what exactly magnetic treatment acts on - on water or on impurities contained in it. There is no such thing as pure water.
The "memory" of water is not limited to the preservation of the effects of magnetic influence. In science, many facts and observations exist and are gradually accumulating, showing that water seems to “remember” that it was frozen before.
Melt water, recently obtained by melting a piece of ice, also seems to be different from the water from which this piece of ice was formed. In melt water, seeds germinate faster and better, sprouts develop faster; further on, as if the chickens that receive melt water grow and develop faster. In addition to the amazing properties of melt water, established by biologists, purely physical and chemical differences are also known, for example, melt water differs in viscosity, in the value of the dielectric constant. The viscosity of melt water takes its usual value for water only 3-6 days after melting. Why this is so (if so), no one knows.
Most researchers call this field of phenomena the "structural memory" of water, believing that all these strange manifestations of the influence of the previous history of water on its properties are explained by a change in the fine structure of its molecular state. Maybe this is so, but ... to name is not the same as to explain. There is still an important problem in science: why and how water “remembers” what happened to it.
Where did water come from on Earth?
Forever, in all directions, the Universe is pierced by streams of cosmic rays - streams of particles with enormous energy. Most of all they contain protons - the nuclei of hydrogen atoms. In its movement in space, our planet is continuously subjected to "proton bombardment". Penetrating the upper layers of the earth's atmosphere, protons capture electrons, turn into hydrogen atoms and immediately react with oxygen to form water. The calculation shows that every year almost one and a half tons of such "cosmic" water is born in the stratosphere. At high altitude at low temperatures, the elasticity of water vapor is very low and water molecules, gradually accumulating, condense on particles of cosmic dust, forming mysterious silvery clouds. Scientists suggest that they consist of the smallest ice crystals that have arisen from such "cosmic" water. The calculation showed that the water that appeared in this way on Earth throughout its history would be just enough to give birth to all the oceans of our planet. So water came to Earth from outer space? But...
Geochemists do not consider water to be a heavenly guest. They are convinced that she earthly origin. The rocks that make up the earth's mantle, which lies between the central core of the Earth and the earth's crust, were melted in places under the influence of the accumulated heat of the radioactive decay of isotopes. Of these, volatile components were released: nitrogen, chlorine, carbon compounds, sulfur, most of all water vapor was released.
How many eruptions could have been ejected by all volcanoes during the entire existence of our planet?
Scientists have calculated this. It turned out that such erupted "geological" water would also be just enough to fill all the oceans.
In the central parts of our planet, which form its core, there is probably no water. It is unlikely that she can exist there. Some scientists believe that further, if both oxygen and hydrogen are present there, then they, together with other elements, should form new for science, unknown metal-like forms of compounds with high density, stable at those enormous pressures and temperatures that prevail in the center of the globe. .
Other researchers are sure that the core of the globe consists of iron. What is actually not so far from us, under our feet, at depths exceeding 3 thousand km, is still unknown to anyone, but there is probably no water there.
Most of the water in the bowels of the Earth is in its mantle - layers located under the earth's crust and extending approximately to a depth of 3 thousand km. Geologists believe that at least 13 billion cubic meters are concentrated in the mantle. km of water.
Most upper layer the earth's shell - the earth's crust contains about another 1.5 billion cubic meters. km of water. Almost all the water in these layers is in a bound state - it is part of the rocks and minerals, forming hydrates. You can't bathe in this water and you won't drink it.
The hydrosphere - the water shell of the globe is formed by about 1.5 billion cubic meters. km of water. Almost all of this amount is contained in the oceans. It occupies about 70% of the entire earth's surface, its area is over 360 million square meters. km. From space, our planet does not look like a globe at all, but rather like a water ball.
The average depth of the Ocean is about 4 km. If we compare this “bottomless depth” with the dimensions of the globe itself, the average diameter of which is equal to km, then, on the contrary, we will have to admit that we live on a wet planet, it is only slightly moistened with water, and even then not over the entire surface. The water in the oceans and seas is salty - you can not drink it.
There is very little water on land: only about 90 million cubic meters. km. Of these, more than 60 million cubic meters. km is underground, almost all of it is salt water. About 25 million cubic meters km of solid water lies in mountainous and glacial regions, in the Arctic, in Greenland, in Antarctica. These water reserves on the globe are reserved.
All lakes, swamps, man-made reservoirs and the soil contain another 500 thousand cubic meters. km of water.
Water is also present in the atmosphere. There is always in the air, even in the most waterless deserts, where there is not a drop of water and it never rains, and then there is a lot of water vapor. In addition, clouds always float across the sky, clouds gather, it snows, it rains, fogs spread over the earth. All these reserves of water in the atmosphere are calculated accurately: all of them, taken together, amount to only 14 thousand cubic meters. km.
The idea of ancient philosophers that everything in nature forms four elements (elements): earth, air, fire and water, existed until the Middle Ages. In 1781, G. Cavendish reported that he had obtained water by burning hydrogen, but did not fully appreciate the importance of his discovery. Later (1783)A. Lavoisier proved that water is not an element at all, but a combination of hydrogen and oxygen. J. Berzelius and P. Dulong (1819), as well as J. Dumas and J. Stas (1842) established the weight composition of water by passing hydrogen through copper oxide, taken in a strictly defined amount, and weighing the formed copper and water. Based on these data, they determined the H:O ratio for water. In addition, in the 1820s, J. Gay-Lussac measured the volumes of gaseous hydrogen and oxygen, which, when interacting, gave water: they were related to each other as 2: 1, which, as we now know, corresponds to the formula H 2 O. Prevalence. Water covers 3/4 of the Earth's surface. The human body is about 70% water, an egg 74%, and some vegetables almost all water. So, in watermelon it is 92%, in ripe tomatoes 95%.Water in natural reservoirs is never homogeneous in composition: it passes through rocks, comes into contact with soil and air, and therefore contains dissolved gases and minerals. Distilled water is cleaner.
Sea water . Compound sea water varies in different regions and depends on the inflow fresh water, evaporation rates, precipitation, iceberg melting, etc.see also OCEAN.Mineral water. Mineral water It is formed when ordinary water seeps through rocks containing compounds of iron, lithium, sulfur and other elements.Soft and hard water. Hard water contains large amounts of calcium and magnesium salts. They dissolve in water when flowing through rocks composed of gypsum (C aSO4 ), limestone (CaCO 3 ) or dolomite (carbonates mg and Sa). In soft water, these salts are few. If the water contains calcium sulfate, then it is said that it has a constant (non-carbonate) hardness. It can be softened by the addition of sodium carbonate; this will cause the calcium to precipitate as carbonate, leaving sodium sulfate in solution. Sodium salts do not react with soap, and its consumption will be less than in the presence of calcium and magnesium salts.Water with temporary (carbonate) hardness contains calcium and magnesium bicarbonates; it can be softened in several ways: 1) by heating, leading to the decomposition of bicarbonates into insoluble carbonates; 2) the addition of lime water (calcium hydroxide), as a result of which bicarbonates are converted into insoluble carbonates; 3) with the help of exchange reactions.
molecular structure. Analysis of data obtained from absorption spectra showed that three atoms in a water molecule form an isosceles triangle with two hydrogen atoms at the base and oxygen at the top:The bond angle HOH is 104.31° , the OH bond length is 0.99Å (1 Å = 10 8 cm), and the distance HH is 1.515 Å . Hydrogen atoms are so deeply “embedded” in the oxygen atom that the molecule is almost spherical; its radius is 1.38Å . WATER Physical properties. Due to the strong attraction between molecules, water has high melting points (0° C) and boiling (100 ° WITH). A thick layer of water has a blue color, which is determined not only by its physical properties, but also by the presence of suspended particles of impurities. The water of mountain rivers is greenish due to the suspended particles of calcium carbonate contained in it. Pure water is a poor conductor of electricity, its electrical conductivity is 1.5 H 10 8 ohm 1 H cm 1 at 0 °C. The compressibility of water is very low: 43 H 10 6 cm 3 per megabar at 20° C. The density of water is maximum at 4° WITH; this is explained by the properties of the hydrogen bonds of its molecules.Vapor pressure. If you leave water in an open container, it will gradually evaporate all its molecules will pass into the air. At the same time, water in a tightly sealed vessel evaporates only partially; at a certain pressure of water vapor between the water and the air above it, an equilibrium is established. The vapor pressure in equilibrium depends on the temperature and is called the saturated vapor pressure (or its elasticity). When the saturation vapor pressure equals the external pressure, the water boils. At normal pressure 760 mm Hg. water boils at 100° C, and at an altitude of 2900 m above sea level, atmospheric pressure drops to 525 mm Hg. and the boiling point is 90° WITH.Evaporation occurs even from the surface of snow and ice, which is why wet laundry dries out in the cold.
The viscosity of water decreases rapidly with increasing temperature and at 100
° C turns out to be 8 times less than at 0° C. Chemical properties. catalytic action. very many chemical reactions flow only in the presence of water. Thus, oxygen oxidation does not occur in dry gases, metals do not react with chlorine, etc.Hydrates. Many compounds always contain a certain number of water molecules and are therefore called hydrates. The nature of the bonds formed in this case can be different. For example, in copper sulfate pentahydrate, or copper sulphate CuSO 4 H 5H 2 O , four water molecules form coordination bonds with the sulfate ion, which are destroyed at 125° WITH; the fifth water molecule is bound so tightly that it breaks off only at a temperature of 250° C. Another stable hydrate sulfuric acid; it exists in two hydrated forms, SO 3 H H 2 O and SO 2 (OH) 2 between which an equilibrium is established. Ions in aqueous solutions are also often hydrated. Yes, N + is always in the form of hydronium ion H 3 O + or H 5 O 2 + ; lithium ion in the form Li (H 2 O) 6 + etc. The elements as such are rarely found in a hydrated form. The exception is bromine and chlorine, which form hydrates Br 2 H 10 H 2 O and Cl 2 H 6H 2 O. Some common hydrates contain water of crystallization, such as barium chloride BaCl 2 H 2H 2 O Epsom salts (magnesium sulfate) MgSO 4 H 7H 2 O , baking soda (sodium carbonate) Na 2 CO 3 H 10 H 2 O, Glauber's salt (sodium sulfate) Na 2 SO 4 H 10 H 2 O. Salts can form several hydrates; So, copper sulfate exists in the form CuSO 4 H 5H 2 O, CuSO 4 H 3H 2 O and CuSO 4 H H 2 O . If the saturation vapor pressure of the hydrate is greater than atmospheric pressure, then the salt will lose water. This process is calledfading (weathering). The process by which salt absorbs water is calledblurring . Hydrolysis. Hydrolysis is a double decomposition reaction in which one of the reactants is water; phosphorus trichloride PCl 3 easily reacts with water: PCl 3 + 3H 2 O \u003d P (OH) 3 + 3HCl Similarly, fats are hydrolyzed to form fatty acids and glycerol.solvation. Water is a polar compound, and therefore readily enters into electrostatic interaction with particles (ions or molecules) of substances dissolved in it. The molecular groups formed as a result of solvation are called solvates. A layer of water molecules bound to the central particle of the solvate by attraction forces constitutes the solvate shell. The concept of solvation was first introduced in 1891 by I.A. Kablukov.Heavy water. In 1931, G. Urey showed that when liquid hydrogen evaporates, its last fractions turn out to be heavier than ordinary hydrogen due to the content of an isotope twice as heavy in them. This isotope is called deuterium and is denoted by the symbol D . In terms of its properties, water containing its heavy isotope instead of ordinary hydrogen differs significantly from ordinary water.In nature, for every 5000 mass parts N
2 Oh accounted for one part D2O . This ratio is the same for river, rain, swamp water, groundwater or crystallization water. Heavy water is used as a label in the study of physiological processes. Thus, in human urine, the ratio between H and D is also equal to 5000:1. If you give the patient to drink water with a high content D2O , then by successively measuring the proportion of this water in the urine, it is possible to determine the rate of excretion of water from the body. It turned out that about half of the water drunk remains in the body even after 15 days. Heavy water, or rather, its deuterium, is an important participant in nuclear fusion reactions.The third isotope of hydrogen is tritium, denoted by the symbol T. Unlike the first two, it is radioactive and is found in nature only in small quantities. In freshwater lakes, the ratio between it and ordinary hydrogen is 1:10
18 , in surface waters 1:10 19 , it is absent in deep waters.see also HYDROGEN. ICE Ice, the solid phase of water, is used primarily as a coolant. It may be in equilibrium with the liquid and gaseous phases or only with the gaseous phase. A thick layer of ice has a bluish color, which is associated with the peculiarities of light refraction. The compressibility of ice is very low.Ice at normal pressure exists only at a temperature of 0
° C or lower and has a lower density than cold water. That is why icebergs float in water. In this case, since the ratio of the densities of ice and water at 0° With constantly, ice always protrudes from the water by a certain part, namely by 1/5 of its volume.see also ICEBERGS. STEAM Steam is the gaseous phase of water. Contrary to popular belief, he is invisible. That “steam” that escapes from a boiling kettle is actually a lot of tiny droplets of water. Steam has properties that are very important for sustaining life on Earth. It is well known, for example, that water evaporates from the surface of the seas and oceans under the influence of solar heat. The resulting water vapor rises into the atmosphere and condenses, and then falls to the ground in the form of rain and snow. Without such a water cycle, our planet would have turned into a desert long ago.Steam has many uses. Some we are familiar with, others we have only heard of. Among the most famous devices and mechanisms working with the use of steam are irons, steam locomotives, steamships, steam boilers. Steam rotates the turbines of generators in thermal power plants.
see also STEAM BOILER; THERMAL ENGINE; HEAT; THERMODYNAMICS.LITERATURE Eisenberg D., Kauzman W.Structure and properties of water . L., 1975Zatsepina G.N. Physical properties and structure of water . M., 1987
Ph.D. O.V. Mosin
MOLECULAR PHYSICS OF WATER IN ITS THREE AGGREGATE STATES
Water, hydrogen oxide, H 2 0, the simplest chemical compound of hydrogen and oxygen that is stable under normal conditions (11.19% hydrogen and 88.81% oxygen by mass). Water is a colorless, odorless and tasteless liquid (in thick layers it has a bluish color), which plays an important role in the geological history of the Earth and the emergence of life, in the formation of the physical and chemical environment, climate and weather on our planet. Water is an essential component of almost all technological processes - both agricultural and industrial production.
Water is part of all living organisms, and in general they contain only half as much water as in all the rivers of the Earth. In living organisms, the amount of water, with the exception of seeds and spores, ranges between 60 and 99.7% by weight. According to the French biologist E. Dubois-Reymond, a living organism is l "eau animée (animate water). All the waters of the Earth constantly interact with each other, as well as with the atmosphere, lithosphere and biosphere.
The globe contains about 16 billion km3 of water, which is 0.25% of the mass of our entire planet. Of this amount, the share of the Earth's hydrosphere (oceans, seas, lakes, rivers, glaciers and groundwater) accounts for 1.386 billion km3. Fresh surface water(lakes and rivers) make up only 0.2 million km3, and atmospheric water vapor - 13 thousand km3.
The total mass of snow and ice distributed over the surface of the Earth reaches approximately 2.5-3.0 x 1016 tons, which is only 0.0004% of the mass of our entire planet. However, this amount is enough to cover the entire surface. globe 53 meter layer, and if all this mass suddenly melted, turning into water, then the level of the World Ocean would have risen by about 64 meters compared to the current one.
The waters of the Earth penetrate it, starting from the highest heights of the stratosphere down to the great depths of the earth's crust, reaching the mantle, and form a continuous shell of the planet - the hydrosphere, which includes all water in liquid, solid, gaseous, chemically and biologically coherent state.
Hydrosphere - the water shell of the Earth, including oceans, seas, lakes, reservoirs, rivers, groundwater, soil moisture, is about 1.4-1.5 billion km 3, and land water accounts for only about 90 million km 3. Of these, groundwater is 60, glaciers 29, lakes 0.75, soil moisture 0.075, rivers 0.0012 million km 3.
The hydrosphere has played and is playing a fundamental role in the geological history of the Earth, in the formation of the physical and chemical environment, climate and weather, in the emergence of life on our planet. It developed together with and in close interaction with the lithosphere, atmosphere, and then living nature.
In the atmosphere water is in the form of steam, fog and clouds, raindrops and snow crystals (about 13-15 thousand km 3 in total). About 10% of the land surface is constantly occupied by glaciers. In the north and northeast of the USSR, in Alaska and the north of Canada - with a total area of \u200b\u200babout 16 million km 2, a subsoil layer of ice is always preserved (about 0.5 million km 3 in total.
IN earth's crust- lithosphere contains, according to various estimates, from 1 to 1.3 billion km3 of water, which is close to its content in the hydrosphere. In the earth's crust, significant amounts of water are in a bound state, being part of certain minerals and rocks (gypsum, hydrated forms of silica, hydrosilicates, etc.). Huge quantities water (13-15 billion km 3) are concentrated in the deeper interior of the Earth's mantle. The release of water released from the mantle during the heating of the Earth in the early stages of its formation, and gave, according to modern views, the beginning of the hydrosphere. The annual inflow of water from the mantle and magma chambers is about 1 km3.
There is evidence that water, at least in part, has a "cosmic" origin: protons that came into the upper atmosphere from the Sun, capturing electrons, turn into hydrogen atoms, which, when combined with oxygen atoms, give H 2 O.
Water occurs in natural conditions in three states: solid - in the form of ice and snow, liquid - in the form of water itself, gaseous - in the form of water vapor. These states of water are called aggregate states, or, respectively, solid, liquid and vapor phases. The transition of water from one phase to another is due to a change in its temperature and pressure. On fig. 1 shows a diagram of the aggregate states of water depending on temperature t and pressure P. From fig.1. it can be seen that in region I, water is only in solid form, in region II - only in liquid form, in region III - only in the form of water vapor. Along the AC curve, it is in a state of equilibrium between the solid and liquid phases (melting of ice and crystallization of water); along the AB curve - in a state of equilibrium between the liquid and gaseous phases (evaporation of water and condensation of steam); along the AD curve - in equilibrium between the solid and gaseous phases (sublimation of water vapor and sublimation of ice).
Rice. 1. Diagram of aggregate states of water in the region of the triple point A. I - ice. II - water. III - water vapor.
The phase equilibrium in Fig. 1 along curves AB, AC, and AD must be understood as dynamic equilibrium, i.e., along these curves, the number of newly formed molecules of one phase is strictly equal to the number of newly formed molecules of the other phase. If, for example, water is gradually cooled at any pressure, then in the limit we will find ourselves on the AC curve, where water will be observed at the appropriate temperature and pressure. If we gradually heat the ice at different pressures, then we will find ourselves on the same equilibrium curve AC, but from the side of the ice. Similarly, we will have water and water vapor, depending on which side we approach the curve AB.
All three curves of the state of aggregation - AC (curve of the dependence of the melting point of ice on pressure), AB (curve of the dependence of the boiling point of water on pressure), AD (curve of the dependence of vapor pressure of the solid phase on temperature) - intersect at one point A, called the triple point . By modern research, the values of saturating vapor pressure and temperature at this point are respectively: P = 610.6 Pa (or 6.1 hPa = 4.58 mmHg), t = 0.01°C (or T = 273.16 TO). In addition to the triple point, curve AB passes through two more characteristic points - a point corresponding to the boiling of water at normal air pressure with coordinates P = 1.013 10 5 Pa and t = 100°C, and a point with coordinates P = 2.211 10 7 Pa and t cr = 374.2 ° C, corresponding to the critical temperature - the temperature, only below which water vapor can be converted into a liquid state by compression.
Curves AC, AB, AD related to the processes of transition of a substance from one phase to another, are described by the Clausius-Clapeyron equation:
where T is the absolute temperature corresponding for each curve, respectively, to the temperature of evaporation, melting, sublimation, etc.; L is the specific heat of evaporation, melting, sublimation, respectively; V 2 - V 1 - the difference in specific volumes, respectively, during the transition from water to ice, from water vapor to water, from water vapor to ice.
Direct experience shows that natural land waters at normal atmospheric pressure are supercooled (AF curve) to some negative temperature values without crystallizing. Thus, water has the property of supercooling, i.e. temperature below the melting point of ice. The supercooled state of water is a metastable (unstable) state in which the transition of the liquid phase to the solid phase, which began at some point, continues continuously until supercooling is eliminated or until the entire liquid turns into a solid. The ability of water to take temperatures below the melting point of ice was first discovered by Fahrenheit as early as 1724.
Thus, ice crystals can only form in supercooled water. The transition of supercooled water into a solid state - ice, occurs only if there are crystallization centers (nuclei) in it, which can be suspended sediment particles in the water, ice or snow crystals entering the water from the atmosphere, ice crystals formed in supercooled water as a result of its turbulent translational motion, particles of other substances present in the water column.
Rice. 2. Phase diagram of water. Ih, II - IX - forms of ice; 1 - 8 - triple points.
Supercooling of water is a thermodynamic state in which the temperature of water is below the temperature of its crystallization. This state arises as a result of a decrease in the temperature of water or an increase in the temperature of its crystallization. The temperature of the water can be lowered by removing heat, which is most common in nature, or by mixing it with salt water, such as sea water. The crystallization temperature can be increased by lowering the pressure.
Under laboratory conditions, at high pressure and intensive cooling, distilled water can be supercooled to a temperature of the order of - 30, and drops - 50 ° C. The rate of its crystallization also depends on the depth of supercooling of water.
Thus, the diagram of aggregate states of water is the solid line AD in fig. 1 - should be considered as referring to very small thermal loads, when the influence of time on the phase transformation is small. At high thermal loads, the process of phase transformations will occur according to the dashed curve AF.
The melting temperature of ice (curve AC) depends very weakly on pressure. In practice, the AC curve is parallel to the horizontal axis: when the pressure changes from 610.6 to 1.013·10 5 Pa, the melting point decreases only from 0.01 to 0°C. However, this temperature decreases with increasing pressure only up to a certain value, then it rises and at very high pressure reaches a value of about 450 ° C (Fig. 1.2). As follows from Fig. 1.2, at high pressure, ice can also be at a positive temperature. There are up to ten different forms of ice. The form of ice Ih, which is characterized by a decrease in the melting point with increasing pressure, corresponds to regular ice formed due to the freezing of water under normal conditions. The coordinates of the triple points of various forms of ice, indicated in Figure 1.2 by Arabic numerals 1-8, are given in Table. 1.1. The structure and physical properties of all forms of ice differ significantly from ice Ih.
A solid body (ice), like a liquid, evaporates in a wide temperature range and directly passes into a gaseous state (sublimation), bypassing the liquid phase - the AD curve. The reverse process, i.e., the transition of the gaseous form directly into the solid (sublimation), is carried out, also bypassing the liquid phase. Sublimation and sublimation of ice and snow play an important role in nature.
The structure of the water molecule
Water represents complex substance, the main structural unit of which is the H 2 O molecule, consisting of two hydrogen atoms and one oxygen atom. Schemes of the possible relative position several dozens of H and O atoms in the H 2 O molecule have been proposed over the entire period of its study; The generally accepted scheme is shown in Fig. 3.
Rice. 3. Scheme of the structure of the water molecule: geometry of the molecule and electron orbits
The total kinetic energy of a triatomic molecule like H 2 O can be described by the following expression:
where and are the speeds of the translational and rotational motion of the molecule, respectively; I x , I y , I z - moments of inertia of the molecule about the corresponding axes of rotation; m is the mass of the molecule.
It can be seen from this equation that the total energy of a triatomic H 2 O molecule consists of six parts corresponding to six degrees of freedom: three translational and three rotational.
It is known from the course of physics that each of these degrees of freedom at thermal equilibrium has the same amount of energy equal to 1/2 kT, where k=R m /N A = 1.3807·10 -23 J/K - Boltzmann's constant; T is absolute temperature; N A \u003d 6.0220 10 23 mol -1 - Avogadro's number; kN A \u003d R m \u003d 8.3144 J / (mol K) - universal gas constant. Then complete kinetic energy such a molecule is equal to:
The total kinetic energy of the molecules contained in a gram-molecule of any gas (vapour) will be:
The total kinetic energy W is related to specific heat cv at constant volume by the formula:
The calculation of the specific heat capacity of water using this formula for water vapor gives a value of 25 J/(mol·K). According to experimental data, for water vapor cv = 27.8 J/(mol·K), i.e. close to the calculated value.
The study of the water molecule using spectrographic studies made it possible to establish that it has the structure of an isosceles triangle, as it were: at the top of this triangle there is an oxygen atom, and at its base there are two hydrogen atoms. The vertex angle is 104°27 and the side length is 0.096 nm. These parameters refer to the hypothetical equilibrium state of the molecule without its oscillations and rotations.
The relative molecular weight of H 2 O depends on the relative atomic mass its constituents and has different meanings, since oxygen and hydrogen have isotopes.
Oxygen has six isotopes: 14 O, 15 O, 16 O, 17 O, 18 O, 19 O, of which only three are stable, and hydrogen has three: 1 H (protium), 2 H (deuterium), 3 H (tritium) . Some of the isotopes are radioactive, have a short half-life and are present in water in small quantities, while others are obtained only artificially and do not occur in nature.
Thus, taking into account the isotopes of oxygen and hydrogen, it is possible to compose from them several types of the H 2 O molecule with different relative molecular masses. Of these, 1 H 2 16 O molecules with relative molecular weights of 18 (ordinary water) and 2 H 2 16 O molecules with relative molecular weights of 20 are the most common. The latter molecules form the so-called heavy water. Heavy water differs significantly from ordinary water in its physical properties.
Molecular-kinetic theory of matter and water
The structure of water in its three states of aggregation cannot yet be considered definitively established. There are a number of hypotheses explaining the structure of steam, water and ice.
These hypotheses are more or less based on the molecular-kinetic theory of the structure of matter, the foundations of which were laid by M.V. Lomonosov. In turn, the molecular-kinetic theory proceeds from the principles classical mechanics, in which molecules (atoms) are considered as regular-shaped balls, electrically neutral, ideally elastic. Such molecules are subject only to mechanical collisions and do not experience any electrical interaction forces. For these reasons, the use of molecular-kinetic theory can only explain the structure of matter in the first approximation.
Gas - in our case, water vapor - according to molecular kinetic theory, is a collection of molecules. The distance between them is many times greater than the size of the molecules themselves. Gas molecules are in continuous random motion, running the path between the walls of the vessels in which the gas is enclosed, and colliding with each other along the way. Molecules collide with each other without loss of mechanical energy; they are considered as collisions of ideally elastic balls. Impacts of molecules on the walls of the vessel limiting them determine the pressure of the gas on these walls. The speed of molecular motion increases with increasing temperature and decreases with decreasing temperature.
When the gas temperature, decreasing from more high values, approaches the boiling point of a liquid (for water, 100°C at normal pressure), the speed of the molecules decreases, and when they collide, the forces of attraction between them become more strength elastic repulsions upon impact and therefore the gas condenses into a liquid.
In the case of artificial liquefaction of a gas, its temperature must be below the so-called critical one, which also corresponds to the critical pressure (clause 1.1). At a temperature above the critical one, a gas (steam) cannot be converted into a liquid by any pressure.
The value of RT cr / (P cr V cr) for all gases, including steam, should be equal to 8/3 = 2.667 (here R is the gas constant; T cr, P cr, V cr are critical temperatures, respectively, pressure, volume). However, for water vapor it is equal to 4.46. This is explained by the fact that the composition of the vapor includes not only single molecules, but also their associations.
A liquid, unlike a gas, is a collection of molecules located so close to each other that forces of mutual attraction appear between them. Therefore, liquid molecules do not scatter in different directions, like gas molecules, but only oscillate around their equilibrium position. At the same time, since the structure of the liquid is not completely dense, there are free places in it - “holes”, as a result, according to the theory of Ya.I. Frenkel, some molecules with greater energy break out of their “sedentary” place and move abruptly into a neighboring “hole” located at a distance approximately equal to the size of the molecule itself. Thus, molecules in a liquid relatively rarely move from place to place, and most of the time they are in a "sedentary" state, only undergoing oscillatory motions. This, in particular, explains the weak diffusion in liquids compared to its high speed in gases. When a liquid is heated, the energy of its molecules increases, the speed of their vibration increases. At a temperature of 100°C and normal atmospheric pressure, water breaks up into individual H2O molecules, the speed of which is already able to overcome the mutual attraction of the molecules, and water turns into steam.
When a liquid (water) is cooled, reverse process. The velocities of the vibrational movement of molecules decrease, the structure of the liquid becomes stronger, and the liquid passes into a crystalline (solid) state - ice. There are two types of solids: crystalline and amorphous. The main feature of crystalline bodies is the anisotropy of their properties in different directions: thermal expansion, strength, optical and electrical properties, etc. Amorphous bodies are isotropic, that is, they have the same properties in all directions. Ice is a crystalline body.
In a solid, unlike a gas and a liquid, each atom or molecule vibrates only around its equilibrium position, but does not move. There are no “holes” in a solid body into which individual molecules can pass. Therefore, there is no diffusion in solids. The atoms that make up the molecules form a strong crystal lattice, the invariance of which is due to molecular forces. When the temperature of a solid approaches its melting point, its crystal lattice collapses and it passes into a liquid state. In contrast to the crystallization of liquids, the melting of solids occurs relatively slowly, without a pronounced jump.
Crystallization of most liquids occurs with a decrease in volume, and the melting of solids is accompanied by an increase in volume. The exceptions are water, antimony, paraffin and some other substances in which the solid phase is less dense than the liquid.
The structure of water in its three states of aggregation
The problem of assessing the structure of water still remains one of the most difficult. Let us briefly consider two generalized hypotheses about the structure of water, which received the greatest recognition, one - in the initial period of development of the doctrine of the structure of water, the other - at the present time.
According to the hypothesis proposed by Whiting (1883) and currently having various interpretations, the basic building block of water vapor is the H 2 O molecule, called hydrol, or monohydrol. The basic building block of water is a double water molecule (H 2 O) 2 -dihydrol; ice consists of triple molecules (H 2 O) 3 - trihydrol. The so-called hydrol theory of the structure of water is based on these ideas.
Water vapor, according to this theory, consists of a collection of the simplest monohydrol molecules and their associations, as well as a small amount of dihydrol molecules.
Liquid water is a mixture of monohydrol, dihydrol and trihydrol molecules. The ratio of the number of these molecules in water is different and depends on temperature. According to this hypothesis, the ratio of the number of water molecules explains one of its main anomalies - the highest density of water at 4°C.
Since the water molecule is asymmetric, the centers of gravity of its positive and negative charges do not coincide. Molecules have two poles - positive and negative, creating, like a magnet, molecular force fields. Such molecules are called polar, or dipoles, and the quantitative characteristic of polarity is determined by the electric moment of the dipole, expressed as the product of the distance l between the electric centers of gravity of the positive and negative charges of the molecule and the charge e in absolute electrostatic units:
For water, the dipole moment is very high: p = 6.13·10 -29 C·m. The polarity of monohydrol molecules explains the formation of dihydrol and trihydrol. At the same time, since the intrinsic velocities of molecules increase with increasing temperature, this can explain the gradual decomposition of trihydrol into dihydrol and then into monohydrol, respectively, during ice melting, heating and boiling of water.
Another hypothesis of the structure of water, developed in the 20th century (models by O.Ya. Samoilov, J. Popla, G.N. Zatsepina and others), is based on the idea that ice, water and water vapor consist of H 2 O molecules combined into groups using the so-called hydrogen bonds (J. Bernal and R. Fowler, 1933). These bonds arise as a result of the interaction of hydrogen atoms of one molecule with an oxygen atom of a neighboring molecule (with a strongly electronegative element). This feature of the hydrogen exchange in the water molecule is due to the fact that, by donating its only electron to the formation covalent bond with oxygen, it remains in the form of a nucleus, almost devoid of an electron shell. Therefore, the hydrogen atom does not experience repulsion from the electron shell of the oxygen of the neighboring water molecule, but, on the contrary, is attracted by it, and can interact with it. According to this hypothesis, it can be assumed that the forces forming a hydrogen bond are purely electrostatic. However, according to the molecular orbital method, the hydrogen bond is formed due to dispersion forces, covalent bonding, and electrostatic interaction.
Table 1 shows the molecular composition of water, ice and water vapor according to various literature sources.
Table 1.1
Molecular composition of ice, water and steam, %
Thus, as a result of the interaction of hydrogen atoms of one water molecule with the negative charges of oxygen of another molecule, four hydrogen bonds are formed for each water molecule. In this case, the molecules, as a rule, are combined into groups - associates: each molecule is surrounded by four others (Fig. 4). This dense packing of molecules is characteristic of frozen water (Ih ice) and leads to an open crystal structure belonging to hexagonal symmetry. With this structure, "voids - channels" are formed between fixed molecules, so the density of ice is less than the density of water.
Increasing the temperature of ice to its melting point and above leads to the breaking of hydrogen bonds. In the liquid state of water, even ordinary thermal motions of molecules are sufficient to destroy these bonds.
Rice. 4. Scheme of interaction of water molecules. 1 - oxygen, 2 - hydrogen, 3 - chemical bond, 4 - hydrogen bond.
With an increase in water temperature to 4°C, the ordering of the arrangement of molecules according to the crystalline type with a characteristic structure for ice is preserved to some extent. The cavities noted above in this structure are filled with released water molecules. As a result, the density of the liquid increases to a maximum at a temperature of 3.98°C. A further increase in temperature leads to distortion and rupture of hydrogen bonds, and, consequently, to the destruction of groups of molecules, up to individual molecules, which is typical for steam.
So what are the mysterious, unusual properties of liquid water familiar to everyone? First of all, in the fact that almost all properties of water are anomalous, and many of them do not obey the logic of those laws of physics that govern other substances.
Water molecules condense to form a liquid substance of amazing complexity. First of all, this is due to the fact that water molecules have a unique property to combine into clusters (groups) (Н 2 О)x. A cluster is usually understood as a group of atoms or molecules united by physical interaction into a single ensemble, but retaining individual behavior within it. The possibilities of direct observation of clusters are limited, and therefore experimenters compensate for instrumental shortcomings with intuition and theoretical constructions.
At room temperature, the degree of association X for water, according to modern data, is from 3 to 6. This means that the formula of water is not just H 2 O, but the average between H 6 O 3 and H 12 O 6. In other words, water is a complex liquid "composed" of repeating groups containing three to six single molecules. As a result, water has anomalous freezing and boiling points compared to homologues. If water obeyed the general rules, it should freeze at a temperature of about -100 o C and boil at a temperature of about +10 o C.
If water during evaporation remained in the form of H 6 O 3, H 8 O 4 or H 12 O 6, then water vapor would be much heavier than air, in which nitrogen and oxygen molecules dominate. In this case, the surface of the entire Earth would be covered with an eternal layer of fog. It is almost impossible to imagine life on such a planet.
People are very lucky: water clusters disintegrate during evaporation, and water turns into almost a simple gas with the chemical formula H 2 O (a small amount of H 4 O 2 dimers recently discovered in steam does not make a difference). The density of gaseous water is less than the density of air, and therefore, water is able to saturate the earth's atmosphere with its molecules, creating comfortable weather conditions for people.
There are no other substances on Earth that are endowed with the ability to be a liquid at the temperatures of human existence and at the same time form a gas that is not only lighter than air, but also capable of returning to its surface in the form of precipitation.
Ph.D. O.V. Mosin
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Water structure
Ph.D. O.V. Mosin
The water molecule is a small dipole containing positive and negative charges at the poles. Since the mass and charge of the oxygen nucleus is greater than that of the hydrogen nuclei, the electron cloud contracts towards the oxygen nucleus. In this case, the hydrogen nuclei are exposed. Thus, the electron cloud has a non-uniform density. Near the hydrogen nuclei there is a lack of electron density, and on the opposite side of the molecule, near the oxygen nucleus, there is an excess of electron density. It is this structure that determines the polarity of the water molecule. If you connect the epicenters of positive and negative charges with straight lines, you get a three-dimensional geometric figure - a regular tetrahedron.
The structure of the water molecule (figure on the right)
Due to the presence of hydrogen bonds, each water molecule forms a hydrogen bond with 4 neighboring molecules, forming an openwork mesh frame in an ice molecule. However, in its liquid state, water is a disordered liquid; these hydrogen bonds are spontaneous, short-lived, quickly break and form again. All this leads to heterogeneity in the structure of water.
Hydrogen bonds between water molecules (picture below on the left)
The fact that water is heterogeneous in its composition was established long ago. It has long been known that ice floats on the surface of water, that is, the density of crystalline ice is less than the density of a liquid.
In almost all other substances, the crystal is denser than the liquid phase. In addition, even after melting, as the temperature rises, the density of water continues to increase and reaches a maximum at 4°C. Less well known is the anomaly of water compressibility: when heated from the melting point up to 40C, it decreases and then increases. The heat capacity of water also depends nonmonotonically on temperature.
In addition, at temperatures below 30C, with an increase in pressure from atmospheric to 0.2 GPa, the viscosity of water decreases, and the self-diffusion coefficient - a parameter that determines the speed of movement of water molecules relative to each other - increases.
For other liquids, the dependence is inverse, and it almost never happens that some important parameter behaves nonmonotonically, i.e. first increased, and after passing the critical value of temperature or pressure decreased. There was an assumption that in fact water is not a single liquid, but a mixture of two components that differ in properties, such as density and viscosity, and, consequently, in structure. Such ideas began to emerge at the end of the 19th century, when a lot of data on water anomalies had accumulated.
The idea that water consists of two components was first proposed by Whiting in 1884. Its authorship is cited by E.F. Fritsman in the monograph "The nature of water. Heavy water", published in 1935. In 1891, W. Rengten introduced the concept of two states of water, which differ in density. After it, many works appeared in which water was considered as a mixture of associates. different composition(hydrols).
When the structure of ice was determined in the 1920s, it turned out that water molecules in the crystalline state form a three-dimensional continuous grid, in which each molecule has four nearest neighbors located at the vertices of a regular tetrahedron. In 1933, J. Bernal and P. Fowler suggested that a similar grid exists in liquid water. Since water is denser than ice, they believed that the molecules in it are not arranged in the same way as in ice, that is, like silicon atoms in the mineral tridymite, but like silicon atoms in a denser modification of silica, quartz. An increase in the density of water upon heating from 0 to 4°C was explained by the presence of a tridymite component at a low temperature. Thus, the Bernal Fowler model retained the element of two-structure, but their main achievement is the idea of a continuous tetrahedral network. Then the famous aphorism of I. Langmuir appeared: "The ocean is one big molecule". Excessive concretization of the model did not add supporters of the theory of a single grid.
It wasn't until 1951 that J. Popple created a continuous grid model that was not as specific as Bernal Fowler's model. Popl imagined water as a random tetrahedral network, the bonds between the molecules in which are curved and have different lengths. Popl's model explains the densification of water during melting by the bending of bonds. When the first definitions of the structure of ices II and IX appeared in the 1960s and 1970s, it became clear how the bending of bonds could lead to structure compaction. Pople's model could not explain the non-monotonicity of the dependence of water properties on temperature and pressure as well as the two-state models. Therefore, the idea of two states was shared by many scientists for a long time.
But in the second half of the 20th century it was impossible to fantasize about the composition and structure of hydrols as much as they did at the beginning of the century. It was already known how ice and crystalline hydrates are arranged, and they knew a lot about hydrogen bonding. In addition to continuum models (Popla model), two groups of mixed models have emerged: cluster and clathrate. In the first group, water appeared as clusters of molecules linked by hydrogen bonds, which floated in a sea of molecules that do not participate in such bonds. Models of the second group considered water as a continuous network (usually called a framework in this context) of hydrogen bonds that contains voids; they contain molecules that do not form bonds with the molecules of the framework. It was not difficult to choose such properties and concentrations of two microphases of cluster models or the properties of the framework and the degree of filling of its voids in clathrate models in order to explain all the properties of water, including the famous anomalies.
Among the cluster models, the most striking was the model of G. Nemethi and H. Sheragi: their pictures, depicting clusters of bound molecules floating in a sea of unbound molecules, have been included in many monographs.
The first model of the clathrate type was proposed in 1946 by O.Ya.Samoilov: a network of hydrogen bonds similar to hexagonal ice is preserved in water, the cavities of which are partially filled with monomeric molecules. L. Pauling in 1959 created another version, suggesting that the network of bonds inherent in some crystalline hydrates can serve as the basis for the structure.
During the second half of the 1960s and the beginning of the 1970s, a convergence of all these views was observed. Variants of cluster models appeared, in which the molecules in both microphases are connected by hydrogen bonds. Supporters of clathrate models began to allow the formation of hydrogen bonds between void and framework molecules. That is, in fact, the authors of these models consider water as a continuous network of hydrogen bonds. And we are talking about how inhomogeneous this grid is (for example, in density). The idea of water as hydrogen-bonded clusters floating in a sea of water molecules devoid of bonds was put to an end in the early eighties, when G. Stanley applied the percolation theory to the water model, which describes the phase transitions of water.
In 1999, the famous Russian water researcher S.V. Zenin defended his doctoral thesis at the Institute of Biomedical Problems of the Russian Academy of Sciences on cluster theory, which was a significant step in the promotion of this area of research, the complexity of which is enhanced by the fact that they are at the intersection of three sciences: physics, chemistry and biology. To them, on the basis of data obtained by three physical and chemical methods: refractometry (S.V. Zenin, B.V. Tyaglov, 1994), high-performance liquid chromatography (S.V. Zenin et al., 1998) and proton magnetic resonance(S.V. Zenin, 1993) a geometric model of the main stable structural formation of water molecules (structured water) was built and proved, and then (S.V. Zenin, 2004) an image was obtained using a phase contrast microscope of these structures.
Science has now proven that the physical properties water and numerous short-lived hydrogen bonds between neighboring hydrogen and oxygen atoms in a water molecule create favorable opportunities for the formation of special associate structures (clusters) that perceive, store and transmit a wide variety of information.
The structural unit of such water is a cluster consisting of clathrates, the nature of which is determined by long-range Coulomb forces. The structure of the clusters encodes information about the interactions that have taken place with these water molecules. In water clusters, due to the interaction between covalent and hydrogen bonds between oxygen atoms and hydrogen atoms, proton migration (Н+) can occur according to the relay mechanism, leading to proton delocalization within the cluster.
Water made up of many clusters various types, forms a hierarchical spatial liquid crystal structure that can perceive and store huge amounts of information.
The figure (V.L. Voeikov) shows diagrams of several simple cluster structures as an example.
Some possible structures of water clusters
Information carriers can be physical fields of the most varied nature. So the possibility of remote information exchange liquid crystal structure of water with objects of various nature using electromagnetic, acoustic and other fields. A person can also be an influencing object.
Water is a source of ultra-weak and weak alternating electromagnetic radiation. Least Chaotic electromagnetic radiation creates structured water. In this case, the induction of the corresponding electromagnetic field can occur, which changes the structural and informational characteristics of biological objects.
In recent years, important data have been obtained on the properties of supercooled water. It is very interesting to study water at a low temperature, because it can be more supercooled than other liquids. Crystallization of water, as a rule, begins on some inhomogeneities either on the walls of the vessel, or on floating particles of solid impurities. Therefore, it is not easy to find the temperature at which supercooled water would spontaneously crystallize. But scientists managed to do this, and now the temperature of the so-called homogeneous nucleation, when the formation of ice crystals occurs simultaneously throughout the volume, is known for pressures up to 0.3 GPa, that is, capturing the regions of existence of ice II.
From atmospheric pressure to the boundary separating ices I and II, this temperature drops from 231 to 180 K, and then slightly increases to 190 K. Below this critical temperature, liquid water is impossible in principle.
Structure of ice (picture on the right)
However, there is one mystery associated with this temperature. In the mid-eighties, a new modification of amorphous ice - ice high density, and this helped to revive the idea of water as a mixture of two states. As prototypes, not crystalline structures were considered, but structures of amorphous ices of different densities. In the most intelligible form, this concept was formulated by E.G. Poniatovsky and V.V. Sinitsin, who wrote in 1999: "Water is considered as a regular solution of two components, the local configurations in which correspond to the short-range order of modifications of amorphous ice." Moreover, by studying the short-range order in supercooled water at high pressure using neutron diffraction methods, scientists were able to find components corresponding to these structures.
As a consequence of the polymorphism of amorphous ices, there were also assumptions about the separation of water into two immiscible components at a temperature below the hypothetical low-temperature critical point. Unfortunately, according to researchers, this temperature at a pressure of 0.017 GPa is 230 K below the nucleation temperature, so no one has yet been able to observe the stratification of liquid water. Thus, the revival of the two-state model raised the question of the inhomogeneity of the network of hydrogen bonds in liquid water. This inhomogeneity can be dealt with only with the help of computer simulation.
Speaking about the crystal structure of water, it should be noted that 14 ice modifications, most of which are not found in nature, in which water molecules both retain their individuality and are connected by hydrogen bonds. On the other hand, there are many variants of the hydrogen bond network in clathrate hydrates. The energies of these networks (high-pressure ices and clathrate hydrates) are not much higher than the energies of cubic and hexagonal ices. Therefore, fragments of such structures can also appear in liquid water. It is possible to design countless different non-periodic fragments, the molecules in which have four nearest neighbors located approximately along the vertices of the tetrahedron, but their structure does not correspond to the structures of known modifications of ice. Numerous calculations have shown that the interaction energies of molecules in such fragments will be close to each other, and there is no reason to say that some structure should prevail in liquid water.
Structural studies of water can be studied by various methods; proton magnetic resonance spectroscopy, infrared spectroscopy, X-ray diffraction, etc. For example, the diffraction of X-rays and neutrons has been studied many times. However, these experiments cannot give detailed information about the structure. Inhomogeneities differing in density could be seen from small angle X-ray and neutron scattering, but such inhomogeneities must be large, consisting of hundreds of water molecules. It would be possible to see them, and investigating the scattering of light. However, water is an exceptionally clear liquid. The only result of diffraction experiments is the radial distribution function, that is, the distance between the atoms of oxygen, hydrogen and oxygen-hydrogen. It can be seen from them that there is no long-range order in the arrangement of water molecules. These functions decay much faster for water than for most other liquids. For example, the distribution of distances between oxygen atoms at a temperature close to room temperature gives only three maxima, at 2.8, 4.5 and 6.7. The first maximum corresponds to the distance to the nearest neighbors, and its value is approximately equal to the length of the hydrogen bond. The second maximum is close to medium length edges of a tetrahedron: remember that water molecules in hexagonal ice are located at the vertices of a tetrahedron circumscribed around the central molecule. And the third maximum, expressed very weakly, corresponds to the distance to the third and more distant neighbors in the hydrogen grid. This maximum itself is not very bright, and there is no need to talk about further peaks. There have been attempts to obtain more detailed information from these distributions. So in 1969, I.S. Andrianov and I.Z. Fisher found the distances up to the eighth neighbor, while it turned out to be 3 to the fifth neighbor, and 3.1 to the sixth. This allows data on the far environment of water molecules to be made.
Another method of studying the structure - neutron diffraction on water crystals is carried out in exactly the same way as x-ray diffraction. However, due to the fact that the neutron scattering lengths do not differ so much for different atoms, the isomorphic substitution method becomes unacceptable. In practice, one usually works with a crystal whose molecular structure has already been approximately established by other methods. The neutron diffraction intensities are then measured for this crystal. Based on these results, a Fourier transform is carried out, during which the measured neutron intensities and phases are used, calculated taking into account non-hydrogen atoms, i.e. oxygen atoms whose position in the structure model is known. Then, on the Fourier map obtained in this way, the hydrogen and deuterium atoms are represented with much greater weights than on the electron density map, because the contribution of these atoms to neutron scattering is very large. From this density map one can, for example, determine the positions of hydrogen atoms (negative density) and deuterium atoms (positive density).
A variation of this method is possible, which consists in the fact that the crystal formed in water is kept in heavy water before measurements. In this case, neutron diffraction not only makes it possible to determine where the hydrogen atoms are located, but also reveals those of them that can be exchanged for deuterium, which is especially important in the study of isotope (H-D) exchange. Such information helps to confirm the correctness of the establishment of the structure.
Other methods also make it possible to study the dynamics of water molecules. These are experiments on quasi-elastic neutron scattering, ultrafast IR spectroscopy and the study of water diffusion using NMR or labeled atoms deuterium. The method of NMR spectroscopy is based on the fact that the nucleus of the hydrogen atom has a magnetic moment-spin, which interacts with magnetic fields, constant and variable. From the NMR spectrum, one can judge the environment in which these atoms and nuclei are located, thus obtaining information about the structure of the molecule.
As a result of experiments on quasi-elastic scattering of neutrons in water crystals, the most important parameter, the self-diffusion coefficient, was measured at various pressures and temperatures. In order to judge the self-diffusion coefficient from the quasi-elastic scattering of neutrons, it is necessary to make an assumption about the nature of molecular motion. If they move in accordance with the model of Ya.I. Frenkel (a well-known Russian theoretical physicist, author of the "Kinetic Theory of Liquids" - a classic book translated into many languages), also called the "jump-waiting" model, then the time of settled life (the time between jumps) of a molecule is 3.2 picoseconds. Latest Methods femtosecond laser spectroscopy made it possible to estimate the lifetime of a broken hydrogen bond: it takes 200 fs for a proton to find a partner. However, these are all averages. To study the details of the structure and nature of the movement of water molecules is possible only with the help of computer simulation, sometimes called a numerical experiment.
This is how the structure of water looks like according to the results of computer simulation (according to the data of Doctor of Chemical Sciences G.G. Malenkov). The general disordered structure can be divided into two types of regions (shown by dark and light balls), which differ in their structure, for example, in the volume of the Voronoi polyhedron (a), the degree of tetrahedrality of the nearest environment (b), the value of potential energy (c), and also in the presence of four hydrogen bonds in each molecule (d). However, these areas literally in a moment, after a few picoseconds, will change their location.
The simulation is done like this. The structure of ice is taken and heated until it melts. Then, after some time for the water to forget its crystalline origin, instant photomicrographs are taken.
To analyze the structure of water, three parameters are selected:
- the degree of deviation of the local environment of the molecule from the vertices of the regular tetrahedron;
-potential energy of molecules;
is the volume of the so-called Voronoi polyhedron.
To construct this polyhedron, one takes an edge from the given molecule to the nearest one, divides it in half, and draws a plane perpendicular to the edge through this point. This is the volume per molecule. The volume of a polyhedron is the density, tetrahedrality, the degree of distortion of hydrogen bonds, energy, the degree of stability of the configuration of molecules. Molecules with close values of each of these parameters tend to group together into separate clusters. Regions of both low and high density have different values energy, but can have the same values. Experiments have shown that regions with different structures, clusters, arise spontaneously and spontaneously decay. The whole structure of water lives and is constantly changing, and the time during which these changes occur is very small. The researchers followed the movements of the molecules and found that they make irregular oscillations with a frequency of about 0.5 ps and an amplitude of 1 angstrom. Rare slow jumps in angstroms, which last picoseconds, were also observed. In general, in 30 ps a molecule can move 8-10 angstroms. The lifetime of the local environment is also small. Regions composed of molecules with close values of the volume of the Voronoi polyhedron can decay in 0.5 ps, and can live for several picoseconds. But the distribution of lifetimes of hydrogen bonds is very large. But this time does not exceed 40 ps, and the average value is several ps.
In conclusion, it should be emphasized that The theory of the cluster structure of water has many pitfalls. For example, Zenin suggests that the main structural element water is a cluster of 57 molecules formed by the fusion of four dodecahedrons. They have common faces, and their centers form a regular tetrahedron. The fact that water molecules can be located at the vertices of a pentagonal dodecahedron has long been known; such a dodecahedron is the basis of gas hydrates. Therefore, there is nothing surprising in the assumption that such structures exist in water, although it has already been said that no particular structure can be dominant and exist for a long time. Therefore, it is strange that this element is assumed to be the main one and that exactly 57 molecules enter into it. From balls, for example, it is possible to assemble the same structures that consist of dodecahedrons adjacent to each other and contain 200 molecules. Zenin, on the other hand, claims that the process of three-dimensional polymerization of water stops at 57 molecules. Larger associates, in his opinion, should not be. However, if this were the case, hexagonal ice crystals, which contain a huge number of molecules bound together by hydrogen bonds, could not precipitate from water vapor. It is not at all clear why the growth of the Zenin cluster stopped at 57 molecules. To avoid contradictions, Zenin also packs clusters into more complex formations - rhombohedrons - of almost a thousand molecules, and the initial clusters do not form hydrogen bonds with each other. Why? How are the molecules on their surface different from those inside? According to Zenin, the pattern of hydroxyl groups on the surface of rhombohedrons provides the memory of water. Consequently, the water molecules in these large complexes are rigidly fixed, and the complexes themselves are solid bodies. Such water will not flow, and its melting point, which is related to molecular weight, must be quite high.
What properties of water does the Zenin model explain? Since the model is based on tetrahedral structures, it can be more or less consistent with X-ray and neutron diffraction data. However, it is unlikely that the model can explain the decrease in density during melting - the packing of dodecahedrons is less dense than ice. But it is most difficult to agree with a model with dynamic properties - fluidity, a large value of the self-diffusion coefficient, short correlation and dielectric relaxation times, which are measured in picoseconds.
Ph.D. O.V. Mosin
References:
G.G. Malenkov. Advances in Physical Chemistry, 2001
S.V. Zenin, B.M. Polanuer, B.V. Tyaglov. Experimental proof of the presence of water fractions. G. Homeopathic medicine and acupuncture. 1997. No. 2. P. 42-46.
S.V. Zenin, B.V. Tyaglov. Hydrophobic model of the structure of associates of water molecules. Zh.Phys.chemistry.1994.T.68.No.4.S.636-641.
S.V. Zenin Investigation of the structure of water by the method of proton magnetic resonance. Dokl.RAN.1993.T.332.No.3.S.328-329.
S.V.Zenin, B.V.Tyaglov. The nature of the hydrophobic interaction. Occurrence of orientational fields in aqueous solutions. J.Phys.chemistry.1994.T.68.No.3.S.500-503.
S.V. Zenin, B.V. Tyaglov, G.B. Sergeev, Z.A. Shabarova. Study of intramolecular interactions in nucleotide amides by NMR. Materials of the 2nd All-Union Conf. By dynamic Stereochemistry. Odessa.1975.p.53.
S.V. Zenin. The structured state of water as the basis for managing the behavior and safety of living systems. Thesis. Doctor of Biological Sciences. State Scientific Center "Institute of Biomedical Problems" (SSC "IMBP"). Defended 1999. 05. 27. UDC 577.32:57.089.001.66.207 p.
IN AND. Slesarev. Research progress report