Water (hydrogen oxide) is a transparent liquid that has no color (in a small volume), smell and taste. Chemical formula: H2O. In the solid state it is called ice or snow, and in the gaseous state it is called water vapor. About 71% of the Earth's surface is covered with water (oceans, seas, lakes, rivers, ice at the poles).

It is a good highly polar solvent. Under natural conditions, it always contains dissolved substances (salts, gases). Water is of key importance in the creation and maintenance of life on Earth, in the chemical structure of living organisms, in the formation of climate and weather.

Almost 70% of the surface of our planet is occupied by oceans and seas. Solid water - snow and ice - covers 20% of the land. Of the total amount of water on Earth, equal to 1 billion 386 million cubic kilometers, 1 billion 338 million cubic kilometers falls on the share of salty waters of the World Ocean, and only 35 million cubic kilometers falls on the share of fresh waters. The total amount of ocean water would be enough to cover the globe with a layer of more than 2.5 kilometers. For each inhabitant of the Earth, there are approximately 0.33 cubic kilometers of sea water and 0.008 cubic kilometers of fresh water. But the difficulty is that the vast majority of fresh water on Earth is in a state that makes it difficult for humans to access. Almost 70% of fresh water is contained in the ice sheets of the polar countries and in mountain glaciers, 30% is in aquifers underground, and only 0.006% of fresh water is simultaneously contained in the channels of all rivers. Water molecules have been found in interstellar space. Water is part of comets, most of the planets of the solar system and their satellites.

The composition of water (by mass): 11.19% hydrogen and 88.81% oxygen. Pure water is clear, odorless and tasteless. It has the highest density at 0°C (1 g/cm3). The density of ice is less than the density of liquid water, so ice floats to the surface. Water freezes at 0°C and boils at 100°C at a pressure of 101,325 Pa. It is a poor conductor of heat and a very poor conductor of electricity. Water is a good solvent. The water molecule has an angular shape; hydrogen atoms form an angle of 104.5° with respect to oxygen. Therefore, the water molecule is a dipole: that part of the molecule where hydrogen is located is positively charged, and the part where oxygen is located is negatively charged. Due to the polarity of water molecules, electrolytes in it dissociate into ions.

In liquid water, along with ordinary H20 molecules, there are associated molecules, i.e., combined into more complex aggregates (H2O)x due to the formation of hydrogen bonds. The presence of hydrogen bonds between water molecules explains the anomalies of its physical properties: maximum density at 4 ° C, high boiling point (in the series H20-H2S - H2Se) anomalously high heat capacity. As the temperature rises, hydrogen bonds break, and a complete break occurs when water changes into steam.

Water is a highly reactive substance. Under normal conditions, it interacts with many basic and acidic oxides, as well as with alkali and alkaline earth metals. Water forms numerous compounds - crystalline hydrates.

Obviously, water-binding compounds can serve as desiccants. Other drying agents include P205, CaO, BaO, metallic Ma (they also chemically interact with water), and silica gel. An important chemical property of water is its ability to enter into hydrolytic decomposition reactions.

Physical properties of water.

Water has a number of unusual features:

1. When ice melts, its density increases (from 0.9 to 1 g/cm³). For almost all other substances, the density decreases when melted.

2. When heated from 0 °C to 4 °C (more precisely, 3.98 °C), water contracts. Accordingly, as it cools, the density decreases. Thanks to this, fish can live in freezing water bodies: when the temperature drops below 4 ° C, colder water, as less dense, remains on the surface and freezes, and a positive temperature remains under the ice.

3. High temperature and specific heat of fusion (0 °C and 333.55 kJ/kg), boiling point (100 °C) and specific heat of vaporization (2250 kJ/kg), compared to hydrogen compounds with similar molecular weight.

4. High heat capacity of liquid water.

5. High viscosity.

6. High surface tension.

7. Negative electric potential of the water surface.

All these features are associated with the presence of hydrogen bonds. Due to the large difference in the electronegativity of hydrogen and oxygen atoms, electron clouds are strongly shifted towards oxygen. Because of this, as well as the fact that the hydrogen ion (proton) does not have internal electron layers and has small dimensions, it can penetrate into the electron shell of a negatively polarized atom of a neighboring molecule. Due to this, each oxygen atom is attracted to the hydrogen atoms of other molecules and vice versa. A certain role is played by the proton exchange interaction between and within water molecules. Each water molecule can participate in a maximum of four hydrogen bonds: 2 hydrogen atoms - each in one, and an oxygen atom - in two; in this state, the molecules are in an ice crystal. When ice melts, some of the bonds break, which allows the water molecules to be packed more densely; when water is heated, the bonds continue to break, and its density increases, but at temperatures above 4 ° C, this effect becomes weaker than thermal expansion. Evaporation breaks all remaining bonds. Breaking bonds requires a lot of energy, hence the high temperature and specific heat of melting and boiling and high heat capacity. The viscosity of water is due to the fact that hydrogen bonds prevent water molecules from moving at different speeds.

For similar reasons, water is a good solvent for polar substances. Each solute molecule is surrounded by water molecules, and the positively charged parts of the solute molecule attract oxygen atoms, and the negatively charged parts attract hydrogen atoms. Because the water molecule is small, many water molecules can surround each solute molecule.

This property of water is used by living beings. In a living cell and in the intercellular space, solutions of various substances in water interact. Water is necessary for the life of all, without exception, unicellular and multicellular living beings on Earth.

Pure (free of impurities) water is a good insulator. Under normal conditions, water is weakly dissociated and the concentration of protons (more precisely, hydronium ions H3O+) and hydroxide ions HO− is 0.1 µmol/L. But since water is a good solvent, certain salts are almost always dissolved in it, that is, positive and negative ions are present in water. As a result, water conducts electricity. The electrical conductivity of water can be used to determine its purity.

Water has a refractive index n=1.33 in the optical range. However, it strongly absorbs infrared radiation, and therefore water vapor is the main natural greenhouse gas responsible for more than 60% of the greenhouse effect. Due to the large dipole moment of the molecules, water also absorbs microwave radiation, on which the principle of the microwave oven is based.

aggregate states.

1. According to the state, they distinguish:

2. Solid - ice

3. Liquid - water

4. Gaseous - water vapor

Fig.1 "Types of snowflakes"

At atmospheric pressure, water freezes (turns into ice) at 0°C and boils (turns into water vapor) at 100°C. As the pressure decreases, the melting point of water slowly rises and the boiling point falls. At a pressure of 611.73 Pa (about 0.006 atm), the boiling and melting points coincide and become equal to 0.01 ° C. This pressure and temperature is called the triple point of water. At lower pressures, water cannot be in a liquid state, and ice turns directly into steam. The sublimation temperature of ice decreases with decreasing pressure.

With an increase in pressure, the boiling point of water increases, the density of water vapor at the boiling point also increases, and liquid water decreases. At a temperature of 374 °C (647 K) and a pressure of 22.064 MPa (218 atm), water passes the critical point. At this point, the density and other properties of liquid and gaseous water are the same. At higher pressures, there is no difference between liquid water and water vapor, hence no boiling or evaporation.

Metastable states are also possible - supersaturated vapor, superheated liquid, supercooled liquid. These states can exist for a long time, but they are unstable and a transition occurs upon contact with a more stable phase. For example, it is not difficult to obtain a supercooled liquid by cooling pure water in a clean vessel below 0 °C, however, when a crystallization center appears, liquid water quickly turns into ice.

Isotopic modifications of water.

Both oxygen and hydrogen have natural and artificial isotopes. Depending on the type of isotopes included in the molecule, the following types of water are distinguished:

1. Light water (just water).

2. Heavy water (deuterium).

3. Superheavy water (tritium).

Chemical properties of water.

Water is the most common solvent on Earth, largely determining the nature of terrestrial chemistry as a science. Most of chemistry, at its inception as a science, began precisely as the chemistry of aqueous solutions of substances. It is sometimes considered as an ampholyte - both an acid and a base at the same time (cation H + anion OH-). In the absence of foreign substances in water, the concentration of hydroxide ions and hydrogen ions (or hydronium ions) is the same, pKa ≈ approx. 16.

Water is a light transparent liquid, colorless in small volumes and acquiring a bluish-greenish color in its thickness. Ice is also transparent, since its absorption coefficient of light in the visible part of the spectrum is practically zero, but this does not apply to the ultraviolet and infrared regions. On the chips of large blocks of glacier and river ice, it, like water, has blue and greenish hues.

The properties of water left their mark on the system of physical constants and units of measurement: the freezing point of water - the melting of ice is accepted

for 0 0 C, and the boiling point of water for 100 0 C (both at atmospheric pressure of about 1013 mbar or hPa = 759.8 mm Hg). Volume unit

in the metric system is chosen from the condition that one cubic meter of water at a temperature of 3.98 0 C has a mass of 1000 kg.

Each water molecule has two hydrogen atoms and two unshared electron pairs and thus can form four hydrogen bonds. The latter are carried out with the participation of a hydrogen atom located either between molecules or between atoms within a molecule:

We will perceive water as an association of molecules united by hydrogen bonds. And if liquid water contains separate associates of its molecules, then a similar arrangement of molecules is also characteristic of ice,

but orderliness already extends to the entire system as a whole, which,

ultimately leads to the formation of the characteristic tetrahedral structure of ice. In other words, ice crystals are entirely built on only one hydrogen bond. The structure of ice is figuratively called "very openwork", because the molecules in it are packed less densely than in liquid water.

Compared to other substances, water is characterized by the highest specific heat capacity, which at a temperature of 15 ° C is

4190 J/(kg*K).

The thermal conductivity of water is very low, but water has a very high latent heat of fusion and evaporation. In order to turn 1 kg of ice into water (latent heat of fusion), it is necessary to spend 330,000 J / kg, and when 1 kg of water evaporates (latent heat of evaporation), 2260 J are spent. These features of water are important for the heat balance of the Earth.

When water freezes, it expands by 9%

to the original volume.

Of all liquids except mercury, water has the highest surface tension.

Another remarkable property of water is the ability to dissolve many substances. Particularly soluble in water are those chemical compounds that can form hydrogen bonds with it. In our daily activities, we are accustomed to consider substances such as alcohol, gasoline, ether, and many others as good solvents, which really dissolve fats and many organics in general, but, for example, salts do not dissolve in them. But the latter dissolve well in water, because. it has an extremely high dielectric constant, and its molecules tend to combine with ions, converting them into hydrated ions, which leads to their stabilization in solution. The good solubility of various salts in water is very important for many natural processes.

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All topics in this section:

The science of hydrology and its relationship with other sciences
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River catchment. Morphometric characteristics of the watershed
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Water balance of the river basin. Elements of water balance
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Precipitation. Interception of precipitation by vegetation
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River and river system
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Heat balance of the river basin. Thermal and ice regime of rivers
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Hydrochemical composition of river waters
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Sea estuarine areas
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physical processes
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Level regime of lakes
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Thermal balance of lakes and thermal regime
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Water is a transparent liquid, colorless (in a small volume) and odorless. Water is of key importance in the creation and maintenance of life on Earth, in the chemical structure of living organisms, in the formation of climate and weather. In the solid state it is called ice or snow, and in the gaseous state it is called water vapor. About 71% of the Earth's surface is covered with water (oceans, seas, lakes, rivers, ice at the poles).

Water properties are a combination of physical, chemical, biochemical, organoleptic, physicochemical and other properties of water.
Water - hydrogen oxide - is one of the most common and important substances. The surface of the Earth occupied by water is 2.5 times the surface of the land. There is no pure water in nature - it always contains impurities. Pure water is obtained by distillation. Distilled water is called distilled. The composition of water (by mass): 11.19% hydrogen and 88.81% oxygen.

Pure water is clear, odorless and tasteless. It has the highest density at 0 ° C (1 g / cm 3). The density of ice is less than the density of liquid water, so ice floats to the surface. Water freezes at 0°C and boils at 100°C at a pressure of 101,325 Pa. It is a poor conductor of heat and a very poor conductor of electricity. Water is a good solvent. The water molecule has an angular shape; hydrogen atoms form an angle of 104.5° with respect to oxygen. Therefore, the water molecule is a dipole: that part of the molecule where hydrogen is located is positively charged, and the part where oxygen is located is negatively charged. Due to the polarity of water molecules, electrolytes in it dissociate into ions.

In liquid water, along with ordinary H20 molecules, there are associated molecules, i.e., combined into more complex aggregates (H2O)x due to the formation of hydrogen bonds. The presence of hydrogen bonds between water molecules explains the anomalies of its physical properties: maximum density at 4 ° C, high boiling point (in the series H20-H2S - H2Se) anomalously high heat capacity. As the temperature rises, hydrogen bonds break, and a complete break occurs when water changes into steam.

Water is a highly reactive substance. Under normal conditions, it interacts with many basic and acidic oxides, as well as with alkali and alkaline earth metals. Water forms numerous compounds - crystalline hydrates.
Obviously, water-binding compounds can serve as desiccants. Other drying agents include P205, CaO, BaO, metallic Ma (they also chemically interact with water), and silica gel. An important chemical property of water is its ability to enter into hydrolytic decomposition reactions.

The chemical properties of water are determined by its composition. Water is 88.81% oxygen and only 11.19% hydrogen. As we mentioned above, water freezes at zero degrees Celsius, but boils at one hundred. Distilled water has a very low concentration of positively charged hydronium ions HO and H3O+ (only 0.1 µmol/l), so it can be called an excellent insulator. However, the properties of water in nature would not be realized correctly if it were not a good solvent. The water molecule is very small in size. When another substance enters the water, its positive ions are attracted to the oxygen atoms that make up the water molecule, and the negative ions are attracted to the hydrogen atoms. Water, as it were, surrounds the chemical elements dissolved in it from all sides. Therefore, water almost always contains various substances, in particular, metal salts, which provide the conduction of electric current.

The physical properties of water "gave" us such phenomena as the greenhouse effect and the microwave oven. About 60% of the greenhouse effect is created by water vapor, which perfectly absorbs infrared rays. In this case, the optical refractive index of water n=1.33. In addition, water also absorbs microwaves due to the high dipole moment of its molecules. These properties of water in nature prompted scientists to think about the invention of the microwave oven.

The role of water in nature and human life is immeasurably great. We can say that all living things consist of water and organic substances. She is an active participant in the formation of the physical and chemical environment, climate and weather. At the same time, it also affects the economy, industry, agriculture, transport and energy.

Without food, we can live for several weeks, but without water - only 2-3 days. To ensure a normal existence, a person must introduce into the body about 2 times more water by weight than nutrients. Loss of more than 10% of water by the human body can lead to death. On average, the body of plants and animals contains more than 50% of water, in the body of a jellyfish up to 96%, in algae 95-99%, in spores and seeds from 7 to 15%. The soil contains at least 20% water, while the human body contains about 65% water. Different parts of the human body contain an unequal amount of water: the vitreous body of the eye consists of 99% water, 83% of it is contained in the blood, 29% in adipose tissue, 22% in the skeleton, and even 0.2% in tooth enamel. Throughout his life, a person loses water from the body, and his bioenergetic potential decreases. In a six-week-old human embryo, the water content is up to 97%, in a newborn - 80%, in an adult - 60-70%, and in the body of an elderly person - only 50-60%.

Water is absolutely essential for all key human life support systems. Water and the substances contained in it become a food medium and supply living organisms with microelements necessary for life. It is contained in the blood (79%) and contributes to the transfer of thousands of essential substances and elements through the circulatory system in a dissolved state (the geochemical composition of water is close to the composition of the blood of animals and humans.).
In the lymph, which carries out the exchange of substances between the blood and tissues of a living organism, water is 98%.
Water, more than other liquids, exhibits the properties of a universal solvent. After a certain time, it can dissolve almost any solid substance.
Such a comprehensive role of water is due to its unique properties.

Recently, the efforts of researchers have been focused on the accelerated study of the processes occurring at the phase boundary. It turned out that water in the boundary layers has many interesting properties that do not appear in the bulk phase. This information is essential for solving a number of important practical problems. An example is the creation of a fundamentally new elemental base of microelectronics, where further miniaturization of circuits will be based on the principle of self-organization of macromolecules on a water surface. A developed surface is also characteristic of biological systems, due to the importance of surface phenomena for their functioning. Almost always, the presence of water has a significant effect on the nature of the processes occurring in the near-surface region. In turn, under the influence of the surface, the properties of the water itself change radically, and the water near the boundary must be considered as a fundamentally new physical object of study. It is very likely that the study of the molecular-statistical properties of water near the surface, which, in essence, is just beginning, will make it possible to effectively control many physical and chemical processes.

Recently, there has been increased interest in studying the properties of water at the microscopic level. Thus, to understand many aspects of the physics of surface phenomena, it is necessary to know the properties of water at the phase boundary. The lack of strict ideas about the structure of water, about the organization of water at the molecular level leads to the fact that when studying the properties of aqueous solutions both in the bulk phase and in capillary systems, water is often considered as a structureless medium. However, it is known that the properties of water in the boundary layers can differ markedly from those in the bulk. Therefore, considering water as a structureless liquid, we lose unique information about the properties of the boundary layers, which, as it turns out, largely determine the nature of the processes occurring in thin pores. For example, the ionic selectivity of cellulose acetate membranes is explained by the special molecular organization of water in the pores, which, in particular, is reflected in the concept of "non-dissolving volume". Further development of the theory that takes into account the specifics of intermolecular interactions underlying selective membrane transport will contribute to a more complete understanding of membrane desalination of solutions. This will make it possible to give sound recommendations for improving the efficiency of water desalination processes. This implies the importance and necessity of studying the properties of liquids in boundary layers, in particular, near the surface of a solid body.



Water surrounds us every day and everywhere - even those who have spent their entire lives in the Sahara Desert. The properties of water often remain invisible to us. And this despite the fact that the structure and properties of water are of great importance for all life on our planet. We are accustomed to taking water for granted, which can be obtained at the first request with a simple movement of the faucet handle. Whereas the unique properties of water are the answer to many questions about our world, although at the same time they pose many questions to researchers.

Basic properties of water

The question of what are the main properties of water can be considered from different angles. The fact is that the physical and chemical properties of water are equally important and determine the special significance and role of this substance in our world. The physical and chemical properties of water are determined by its special structure. Everyone knows that a water molecule consists of two hydrogen atoms and an oxygen atom. However, already from this simple fact, the anomalous properties of water begin: since all other hydrogen compounds under normal conditions have a gaseous state of aggregation, while water is liquid. In addition, it is water that can be in three states of aggregation (gaseous, liquid, solid) and quite easily pass from one to another.

The unusual properties of ordinary water are due to the fact that hydrogen atoms are connected to the oxygen atom at a strictly defined angle and do not change their position. As a result, strong interatomic bonds are formed, which are quickly fixed with decreasing temperature. This explains why the difference between the normal temperature of water and its freezing point is much smaller than between the "average" temperature and the boiling point. When freezing, no energy is spent on breaking interatomic bonds, so the molecules quickly form ordered structures and turn into ice crystals. In order to go into a gaseous state, those very strong bonds in the water molecules must be destroyed - that is why, for boiling, water needs to be heated longer with the expenditure of a large amount of thermal energy.

Features of the molecular structure of water give an answer to the question why the importance of water for living organisms and in general for the existence of life is so great. Since the only currently known form of life in the universe , terrestrial, cannot exist without water. The biological properties of water are such that its molecules are smaller in relation to the molecules of other substances. Perhaps the first answer to the question of what properties water has should be "the ability to dissolve." Dissolution in water is nothing more than the surrounding of a substance molecule from all sides by water molecules. Water is a medium outside of which a living cell cannot arise, exist and develop. Because for the life of a cell, the interaction of various substances is necessary, which is provided precisely by the informational properties of water, which is capable of carrying molecules of other substances. So the role of water in living organisms is extremely simple - no living organisms would exist without water.

Physical properties of water

The basic physical properties of water depend primarily on environmental factors such as pressure and temperature. The thermal environment in general is extremely important for water: the residence and transition to various aggregate states of water are associated with temperature. Interesting properties of water are, in particular, that absolutely pure, that is, free of impurities and dissolved substances, water can be in the so-called metastable states. For example, the thermal properties of water allow pure water not to freeze to temperatures below "minus 30" degrees Celsius, or to remain in a liquid state, heating up to 200 degrees Celsius. However, such metastable states are extremely unstable, moreover, absolutely pure water is practically never found in natural conditions. So the calculation of the thermophysical properties of water is carried out, with the exception of special cases, based on standard boundaries - 0 degrees as the freezing point, 100 degrees as the boiling point.

Of course, the thermophysical properties of water are far from the only characteristics of this unique substance. There is a table of physical properties of water, which contains detailed information about it. For example, you can learn that the special properties of water make it a good insulator, that is, it conducts electricity very poorly. But we are talking about absolutely pure water - ordinary water, which has many different dissolved substances in it, is a good electrical conductor. In addition, the table contains indicators such as, for example, the speed of sound, which in water at a temperature of 20 degrees is 1482.7 meters per second (for comparison, the speed of sound in air is 331 meters per second).

Chemical properties of water

The main chemical property of water is its ability to be a solvent. The acidic properties of water are being actively studied, since water, no matter how unexpected it may seem, is an acid. In chemical science, an acid is considered a substance capable of giving up hydrogen cations during a chemical interaction. Water is just capable of this, which is why the oxidizing properties of water are so important. But that's why water is a unique substance that, in addition to oxidizing, also has reducing properties.

It should be recalled that in biochemistry, redox reactions are called such chemical interactions, during which electrons are added or donated, which leads to a change in the electrical potential of substances. Oxygen is an active oxidizing agent, that is, a substance that picks up the electrodes; hydrogen is a universal reducing agent, willingly giving up hydrogens. So it turns out that water, consisting of oxygen and hydrogen, can be both an oxidizing agent and a reducing agent - hence the redox properties of water. The aqueous environment can be oxidizing, taking electrons from other substances - this position is typical for most situations with water on the surface. Water can be redox, provided it contains certain impurities. Finally, it can also be a reducing medium, which is typical for groundwater saturated with metals.

Water - one of the most amazing compounds on Earth - has long amazed researchers with the unusualness of many of its physical properties:

1) Inexhaustibility as a substance and natural resource; if all other resources of the earth are destroyed or dissipated, then water, as it were, escapes from this, taking on various forms or states: in addition to liquid, solid and gaseous. It is the only substance and resource of this type. This property ensures the omnipresence of water, it permeates the entire geographic envelope of the Earth and performs a variety of work in it.

2) The expansion inherent only to it during solidification (freezing) and a decrease in volume during melting (transition to a liquid state).

3) The maximum density at a temperature of +4 ° C and the very important properties associated with this for natural and biological processes, for example, the exclusion of deep freezing of water bodies. As a rule, the maximum density of physical bodies is observed at the solidification temperature. The maximum density of distilled water is observed under abnormal conditions - at a temperature of 3.98-4 ° C (or rounded +4 ° C), i.e. at a temperature above the solidification (freezing) point. When the water temperature deviates from 4 °C in both directions, the density of water decreases.

4) When melting (melting), ice floats on the surface of water (unlike other liquids).

5) An anomalous change in the density of water entails the same anomalous change in the volume of water when heated: with an increase in temperature from 0 to 4 ° C, the volume of heated water decreases and only with a further increase does it begin to increase. If, with a decrease in temperature and during the transition from a liquid to a solid state, the density and volume of water changed in the same way as it happens with the vast majority of substances, then when winter approaches, the surface layers of natural waters would cool to 0 ° C and sink to the bottom, freeing up space. warmer layers, and so it would continue until the entire mass of the reservoir would have acquired a temperature of 0 ° C. Further, the water would begin to freeze, the resulting ice floes would sink to the bottom, and the reservoir would freeze to its entire depth. At the same time, many forms of life in water would be impossible. But since water reaches its highest density at 4 °C, the movement of its layers caused by cooling ends when this temperature is reached. With a further decrease in temperature, the cooled layer, which has a lower density, remains on the surface, freezes, and thereby protects the underlying layers from further cooling and freezing.

6) The transition of water from one state to another is accompanied by costs (evaporation, melting) or release (condensation, freezing) of the corresponding amount of heat. It takes 677 cal to melt 1 g of ice, and 80 cal less to evaporate 1 g of water. The high latent heat of ice melting ensures slow melting of snow and ice.

7) The ability to relatively easily pass into a gaseous state (evaporate) not only at positive, but also at negative temperatures. In the latter case, evaporation occurs bypassing the liquid phase - from the solid (ice, snow) immediately into the vapor phase. This phenomenon is called sublimation.

8) If we compare the boiling and freezing points of hydrides formed by elements of the sixth group of the periodic table (selenium H 2 Se, tellurium H 2 Te) and water (H 2 O), then by analogy with them, the boiling point of water should be about 60 ° C, and the freezing point is below 100 ° C. But even here the anomalous properties of water are manifested - at a normal pressure of 1 atm. Water boils at +100°C and freezes at 0°C.

9) Of great importance in the life of nature is the fact that water has an anomalously high heat capacity, 3,000 times greater than air. This means that when 1 m 3 of water is cooled by 1 0 C, 3000 m 3 of air is heated by the same amount. Therefore, by accumulating heat, the Ocean has a softening effect on the climate of coastal areas.

10) Water absorbs heat during evaporation and melting, releasing it during condensation from steam and freezing.

11) The ability of water in dispersed media, for example, in finely porous soils or biological structures, to go into a bound or dispersed state. In these cases, the properties of water (its mobility, density, freezing point, surface tension, and other parameters), which are extremely important for the processes in natural and biological systems, change very much.

12) Water is a universal solvent, therefore, not only in nature, but also in laboratory conditions, there is no ideally pure water for the reason that it is capable of dissolving any vessel in which it is enclosed. There is an assumption that the surface tension of ideally pure water would be such that it would be possible to skate on it. The ability of water to dissolve ensures the transfer of substances in a geographical envelope, underlies the exchange of substances between organisms and the environment, and is the basis of nutrition.

13) Of all liquids (except mercury), water has the highest surface pressure and surface tension: \u003d 75 10 -7 J / cm 2 (glycerin - 65, ammonia - 42, and all the rest - below 30 10 -7 J / cm 2). Because of this, a drop of water tends to take the form of a ball, and when it comes into contact with solids, it wets the surface of most of them. That is why it can rise up the capillaries of rocks and plants, providing soil formation and plant nutrition.

14) Water has high thermal stability. Water vapor begins to decompose into hydrogen and oxygen only at temperatures above 1000 °C.

15) Chemically pure water is a very poor conductor of electricity. Due to the low compressibility, sound and ultrasonic waves propagate well in water.

16) The properties of water change greatly under the influence of pressure and temperature. So, with an increase in pressure, the boiling point of water rises, and the freezing point, on the contrary, decreases. As the temperature rises, the surface tension, density and viscosity of water decrease and the electrical conductivity and speed of sound in water increase.

The anomalous properties of water taken together, indicating its extremely high resistance to external factors, are caused by the presence of additional forces between molecules, called hydrogen bonds. The essence of a hydrogen bond is that a hydrogen ion bound to some ion of another element is able to electrostatically attract an ion of the same element from another molecule. The water molecule has an angular structure: the nuclei included in its composition form an isosceles triangle, at the base of which there are two protons, and at the top is the nucleus of the oxygen atom (Figure 2.2).

Figure 2.2 - The structure of the water molecule

Of the 10 electrons (5 pairs) present in the molecule, one pair (internal electrons) is located near the oxygen nucleus, and of the remaining 4 pairs of electrons (external), one pair is socialized between each of the protons and the oxygen nucleus, while 2 pairs remain undefined and are directed to the opposite vertices of the tetrahedron from the protons. Thus, in a water molecule there are 4 charge poles located at the vertices of the tetrahedron: 2 negative ones, created by an excess of electron density at the locations of unshared pairs of electrons, and 2 positive ones, created by its deficiency at the locations of protons.

As a result, the water molecule turns out to be an electric dipole. The positive pole of one water molecule attracts the negative pole of another water molecule. The result is aggregates (or associations of molecules) of two, three or more molecules (Figure 2.3).

Figure 2.3 - Formation of associated molecules by water dipoles:

1 - monohydrol H 2 O; 2 - dihydrol (H 2 O) 2; 3 - trihydrol (H 2 O) 3

Therefore, single, double and triple molecules are simultaneously present in water. Their content varies with temperature. Ice contains mainly trihydrols, the volume of which is greater than monohydrols and dihydrols. With an increase in temperature, the speed of movement of molecules increases, the forces of attraction between molecules weaken, and in the liquid state, water is a mixture of tri-, di- and monohydrols. With a further increase in temperature, trihydrol and dihydrol molecules decompose; at a temperature of 100 ° C, water consists of monohydrols (steam).

The existence of unshared electron pairs determines the possibility of the formation of two hydrogen bonds. Two more bonds arise due to two hydrogen atoms. As a result, each water molecule is able to form four hydrogen bonds (Figure 2.4).

Figure 2.4 - Hydrogen bonds in water molecules:

– hydrogen bond designation

Due to the presence of hydrogen bonds in water, a high degree of order is noted in the arrangement of its molecules, which brings it closer to a solid body, and numerous voids appear in the structure, making it very loose. The structure of ice belongs to the least dense structures. There are voids in it, the dimensions of which somewhat exceed the dimensions of the H 2 O molecule. When ice melts, its structure is destroyed. But even in liquid water, hydrogen bonds between molecules are preserved: associates appear - the embryos of crystalline formations. In this sense, water is, as it were, in an intermediate position between the crystalline and liquid states and is more similar to a solid than to an ideal liquid. However, unlike ice, each associate exists for a very short time: the destruction of some and the formation of other aggregates are constantly taking place. In the voids of such "ice" aggregates, single water molecules can be placed, while the packing of water molecules becomes denser. That is why when ice melts, the volume occupied by water decreases, its density increases. At + 4 °C, water has the densest packing.

When water is heated, part of the heat is spent on breaking hydrogen bonds. This explains the high heat capacity of water. Hydrogen bonds between water molecules are completely destroyed when water passes into steam.

The complexity of the structure of water is due not only to the properties of its molecule, but also to the fact that, due to the existence of oxygen and hydrogen isotopes, water contains molecules with different molecular weights (from 18 to 22). The most common is the "regular" molecule with a molecular weight of 18. The content of molecules with a large molecular weight is small. Thus, "heavy water" (molecular weight 20) is less than 0.02% of all water reserves. It is not found in the atmosphere, in a ton of river water it is no more than 150 g, sea water - 160-170 g. However, its presence gives "ordinary" water a greater density, affects its other properties.

The amazing properties of water allowed the emergence and development of life on Earth. Thanks to them, water can play an indispensable role in all processes occurring in the geographic envelope.