Types of crystal lattices. Crystal lattices At the nodes of the crystal lattice of dry ice are

Chemistry is an amazing science. So much incredible can be found in seemingly ordinary things.

Everything material that surrounds us everywhere exists in several states of aggregation: gases, liquids and solids. Scientists have also isolated the 4th - plasma. At a certain temperature, a substance can change from one state to another. For example, water: when heated above 100, from a liquid form, it turns into steam. At temperatures below 0, it passes into the next aggregate structure - ice.

In contact with

The entire material world has in its composition a mass of identical particles that are interconnected. These smallest elements are strictly arranged in space and form the so-called spatial framework.

Definition

A crystal lattice is a special structure of a solid substance, in which the particles are in a geometrically strict order in space. It is possible to detect nodes in it - places where elements are located: atoms, ions and molecules and internodal space.

Solids, depending on the range of high and low temperatures, are crystalline or amorphous - they are characterized by the absence of a specific melting point. When exposed to elevated temperatures, they soften and gradually turn into a liquid form. Such substances include: resin, plasticine.

In this regard, it can be divided into several types:

• atomic;
• ionic;
• molecular;
• metal.

But at different temperatures, one substance can have different forms and exhibit diverse properties. This phenomenon is called allotropic modification.

Atomic type

In this type, atoms of one or another substance are located at the nodes, which are connected by covalent bonds. This type of bond is formed by a pair of electrons of two neighboring atoms. Due to this, they are connected evenly and in a strict order.

Substances with an atomic crystal lattice are characterized by the following properties: strength and high melting point. This type of bond is present in diamond, silicon and boron..

Ionic type

Oppositely charged ions are located at the nodes that create an electromagnetic field that characterizes the physical properties of a substance. These will include: electrical conductivity, refractoriness, density and hardness. Table salt and potassium nitrate are characterized by the presence of an ionic crystal lattice.

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Molecular type

In sites of this type, there are ions bound together by van der Waals forces. Due to weak intermolecular bonds, such substances, for example, ice, carbon dioxide and paraffin, are characterized by plasticity, electrical and thermal conductivity.

metal type

In its structure, it resembles a molecular one, but it still has stronger bonds. The difference of this type is that positively charged cations are located at its nodes. The electrons that are in the interstitial space, participate in the formation of an electric field. They are also called electric gas.

Simple metals and alloys are characterized by a metallic lattice type. They are characterized by the presence of metallic luster, plasticity, thermal and electrical conductivity. They can melt at different temperatures.

O. V. Mosin, I. Ignatov (Bulgaria)

annotation The importance of ice in sustaining life on our planet cannot be underestimated. Ice has a great influence on the living conditions and life of plants and animals and on various types of human economic activity. Covering the water, ice, due to its low density, plays the role of a floating screen in nature, protecting rivers and reservoirs from further freezing and preserving the life of underwater inhabitants. The use of ice for various purposes (snow retention, arrangement of ice crossings and isothermal warehouses, ice laying of storage facilities and mines) is the subject of a number of sections of hydrometeorological and engineering sciences, such as ice technology, snow technology, engineering permafrost, as well as the activities of special services for ice reconnaissance, icebreaking transport and snowplows. Natural ice is used to store and cool food products, biological and medical preparations, for which it is specially produced and harvested, and melt water prepared by melting ice is used in folk medicine to increase metabolism and remove toxins from the body. The article introduces the reader to new little-known properties and modifications of ice.

Ice is a crystalline form of water, which, according to the latest data, has fourteen structural modifications. Among them there are both crystalline (natural ice) and amorphous (cubic ice) and metastable modifications that differ from each other in the mutual arrangement and physical properties of water molecules linked by hydrogen bonds that form the crystal lattice of ice. All of them, except for the familiar natural ice I h, which crystallizes in a hexagonal lattice, are formed under exotic conditions - at very low temperatures of dry ice and liquid nitrogen and high pressures of thousands of atmospheres, when the angles of hydrogen bonds in a water molecule change and crystalline systems are formed that are different from hexagonal. Such conditions are reminiscent of cosmic conditions and are not found on Earth.

In nature, ice is represented mainly by one crystalline variety, crystallizing in a hexagonal lattice resembling a diamond structure, where each water molecule is surrounded by four molecules closest to it, located at the same distance from it, equal to 2.76 angstroms and located at the vertices of a regular tetrahedron. Due to the low coordination number, the structure of ice is a network, which affects its low density, which is 0.931 g/cm 3 .

The most unusual property of ice is the amazing variety of external manifestations. With the same crystal structure, it can look completely different, taking the form of transparent hailstones and icicles, fluffy snow flakes, a dense shiny crust of ice, or giant glacial masses. Ice occurs in nature in the form of continental, floating and underground ice, as well as in the form of snow and hoarfrost. It is widespread in all areas of human habitation. Collecting in large quantities, snow and ice form special structures with fundamentally different properties than individual crystals or snowflakes. Natural ice is formed mainly by ice of sedimentary-metamorphic origin, formed from solid atmospheric precipitation as a result of subsequent compaction and recrystallization. A characteristic feature of natural ice is granularity and banding. Granularity is due to recrystallization processes; each grain of glacial ice is an irregularly shaped crystal that closely adjoins other crystals in the ice mass in such a way that the protrusions of one crystal fit tightly into the depressions of another. Such ice is called polycrystalline. In it, each ice crystal is a layer of the thinnest leaves overlapping each other in the basal plane perpendicular to the direction of the optical axis of the crystal.

The total reserves of ice on Earth are estimated to be about 30 million tons. km 3(Table 1). Most of the ice is concentrated in Antarctica, where the thickness of its layer reaches 4 km. There is also evidence of the presence of ice on the planets of the solar system and in comets. Ice is so important for the climate of our planet and the habitation of living beings on it that scientists have designated a special environment for ice - the cryosphere, the boundaries of which extend high into the atmosphere and deep into the earth's crust.

Tab. one. Quantity, distribution and lifetime of ice.

• Type of ice; Weight; Distribution area; Average concentration, g/cm2; Weight gain rate, g/year; Average life time, year
• G; %; million km2; %
• Glaciers; 2.4 1022; 98.95; 16.1; 10.9 sushi; 1.48 105; 2.5 1018; 9580
• underground ice; 2 1020; 0.83; 21; 14.1 sushi; 9.52 103; 6 1018; 30-75
• sea ​​ice; 3.5 1019; 0.14; 26; 7.2 oceans; 1.34 102; 3.3 1019; 1.05
• Snow cover; 1.0 1019; 0.04; 72.4; 14.2 Earths; 14.5; 2 1019; 0.3-0.5
• icebergs; 7.6 1018; 0.03; 63.5; 18.7 ocean; 14.3; 1.9 1018; 4.07
• atmospheric ice; 1.7 1018; 0.01; 510.1; 100 Earth; 3.3 10-1; 3.9 1020; 4 10-3

Ice crystals are unique in their shape and proportions. Any growing natural crystal, including an ice crystal of ice, always strives to create an ideal, regular crystal lattice, since this is beneficial from the point of view of a minimum of its internal energy. Any impurities, as is known, distort the shape of the crystal, therefore, during the crystallization of water, water molecules are first of all built into the lattice, and foreign atoms and molecules of impurities are displaced into the liquid. And only when the impurities have nowhere to go, the ice crystal begins to build them into its structure or leaves them in the form of hollow capsules with a concentrated non-freezing liquid - brine. Therefore, sea ice is fresh and even the dirtiest water bodies are covered with transparent and clean ice. When ice melts, it displaces impurities into the brine. On a planetary scale, the phenomenon of freezing and thawing of water, along with the evaporation and condensation of water, plays the role of a gigantic cleansing process in which water on Earth is constantly purifying itself.

Tab. 2. Some physical properties of ice I.

Property

Meaning

Note

Heat capacity, cal/(g °C) Heat of melting, cal/g Heat of vaporization, cal/g

0.51 (0°C) 79.69 677

Decreases strongly with decreasing temperature

Thermal expansion coefficient, 1/°C

9.1 10-5 (0°C)

Polycrystalline ice

Thermal conductivity, cal/(cm sec °C)

4.99 10 -3

Polycrystalline ice

Refractive index:

1.309 (-3°C)

Polycrystalline ice

Specific electrical conductivity, ohm-1 cm-1

10-9 (0°C)

Apparent activation energy 11 kcal/mol

Surface electrical conductivity, ohm-1

10-10 (-11°C)

Apparent activation energy 32 kcal/mol

Young's modulus of elasticity, dyne/cm2

9 1010 (-5 °C)

Polycrystalline ice

Resistance, MN/m2: crushing tear shear

2,5 1,11 0,57

polycrystalline ice polycrystalline ice polycrystalline ice

Dynamic viscosity, poise

Polycrystalline ice

Activation energy during deformation and mechanical relaxation, kcal/mol

Increases linearly by 0.0361 kcal/(mol °C) from 0 to 273.16 K

Note: 1 cal/(g °C)=4.186 kJ/(kg K); 1 ohm -1 cm -1 \u003d 100 sim / m; 1 dyn = 10 -5 N ; 1 N = 1 kg m/s²; 1 dyne/cm=10 -7 N/m; 1 cal / (cm sec ° C) \u003d 418.68 W / (m K); 1 poise \u003d g / cm s \u003d 10 -1 N sec / m 2.

Due to the wide distribution of ice on Earth, the difference in the physical properties of ice (Table 2) from the properties of other substances plays an important role in many natural processes. Ice has many other life-supporting properties and anomalies - anomalies in density, pressure, volume, and thermal conductivity. If there were no hydrogen bonds linking water molecules into a crystal, ice would melt at -90 °C. But this does not happen due to the presence of hydrogen bonds between water molecules. Due to its lower density than that of water, ice forms a floating cover on the surface of the water, which protects rivers and reservoirs from bottom freezing, since its thermal conductivity is much less than that of water. At the same time, the lowest density and volume are observed at +3.98 °C (Fig. 1). Further cooling of water to 0 0 C gradually leads not to a decrease, but to an increase in its volume by almost 10%, when the water turns into ice. This behavior of water indicates the simultaneous existence of two equilibrium phases in water - liquid and quasi-crystalline, by analogy with quasi-crystals, the crystal lattice of which not only has a periodic structure, but also has symmetry axes of different orders, the existence of which previously contradicted the ideas of crystallographers. This theory, first put forward by the well-known domestic theoretical physicist Ya. I. Frenkel, is based on the assumption that some of the liquid molecules form a quasi-crystalline structure, while the rest of the molecules are gas-like, freely moving through the volume. The distribution of molecules in a small neighborhood of any fixed water molecule has a certain order, somewhat reminiscent of a crystalline one, although more loose. For this reason, the structure of water is sometimes called quasi-crystalline or crystal-like, i.e., having symmetry and the presence of order in the mutual arrangement of atoms or molecules.

Rice. one. The dependence of the specific volume of ice and water on temperature

Another property is that the speed of ice flow is directly proportional to the activation energy and inversely proportional to the absolute temperature, so that as the temperature decreases, ice approaches in its properties an absolutely solid body. On average, at a temperature close to melting, the fluidity of ice is 10 6 times higher than that of rocks. Due to its fluidity, ice does not accumulate in one place, but constantly moves in the form of glaciers. The relationship between flow velocity and stress in polycrystalline ice is hyperbolic; with an approximate description of it by a power equation, the exponent increases as the voltage increases.

Visible light is practically not absorbed by ice, since light rays pass through the ice crystal, but it blocks ultraviolet radiation and most of the infrared radiation from the Sun. In these regions of the spectrum, ice appears absolutely black, since the absorption coefficient of light in these regions of the spectrum is very high. Unlike ice crystals, white light falling on snow is not absorbed, but is refracted many times in ice crystals and reflected from their faces. That's why snow looks white.

Due to the very high reflectivity of ice (0.45) and snow (up to 0.95), the area covered by them is on average about 72 million hectares per year. km 2 in the high and middle latitudes of both hemispheres, it receives solar heat 65% less than the norm and is a powerful source of cooling of the earth's surface, which largely determines the modern latitudinal climatic zonality. In summer, in the polar regions, solar radiation is greater than in the equatorial belt, nevertheless, the temperature remains low, since a significant part of the absorbed heat is spent on melting ice, which has a very high melting heat.

Other unusual properties of ice include the generation of electromagnetic radiation by its growing crystals. It is known that most of the impurities dissolved in water are not transferred to the ice when it begins to grow; they freeze. Therefore, even on the dirtiest puddle, the ice film is clean and transparent. In this case, impurities accumulate at the boundary of solid and liquid media, in the form of two layers of electric charges of different signs, which cause a significant potential difference. The charged layer of impurities moves along with the lower boundary of the young ice and radiates electromagnetic waves. Thanks to this, the crystallization process can be observed in detail. Thus, a crystal growing in length in the form of a needle radiates differently than one covered with lateral processes, and the radiation of growing grains differs from that which occurs when crystals crack. From the shape, sequence, frequency and amplitude of the radiation pulses, it is possible to determine with what speed the ice freezes and what kind of ice structure is formed in this case.

But the most surprising thing about the structure of ice is that water molecules at low temperatures and high pressures inside carbon nanotubes can crystallize in the form of a double helix, reminiscent of DNA molecules. This has been proven by recent computer experiments by American scientists led by Xiao Cheng Zeng from the University of Nebraska (USA). In order for water to form a spiral in a simulated experiment, it was placed in nanotubes with a diameter of 1.35 to 1.90 nm under high pressure, varying from 10 to 40,000 atmospheres, and a temperature of –23 °C was set. It was expected to see that the water in all cases forms a thin tubular structure. However, the model showed that at a nanotube diameter of 1.35 nm and an external pressure of 40,000 atmospheres, the hydrogen bonds in the ice structure were bent, which led to the formation of a double-walled helix - internal and external. Under these conditions, the inner wall turned out to be twisted into a quadruple helix, and the outer wall consisted of four double helixes similar to a DNA molecule (Fig. 2). This fact can serve as confirmation of the connection between the structure of the vitally important DNA molecule and the structure of water itself and that water served as a matrix for the synthesis of DNA molecules.

Rice. 2. Computer model of the structure of frozen water in nanotubes, resembling a DNA molecule (Photo from New Scientist, 2006)

Another of the most important properties of water discovered recently is that water has the ability to remember information about past exposures. This was first proved by the Japanese researcher Masaru Emoto and our compatriot Stanislav Zenin, who was one of the first to propose a cluster theory of the structure of water, consisting of cyclic associates of a bulk polyhedral structure - clusters of the general formula (H 2 O) n, where n, according to recent data, can reach hundreds and even thousand units. It is due to the presence of clusters in water that water has informational properties. The researchers photographed the processes of water freezing into ice microcrystals, acting on it with various electromagnetic and acoustic fields, melodies, prayer, words or thoughts. It turned out that under the influence of positive information in the form of beautiful melodies and words, the ice froze into symmetrical hexagonal crystals. Where non-rhythmic music sounded, angry and insulting words, water, on the contrary, froze into chaotic and shapeless crystals. This is proof that water has a special structure that is sensitive to external information influences. Presumably, the human brain, which consists of 85-90% of water, has a strong structuring effect on water.

Emoto crystals arouse both interest and insufficiently substantiated criticism. If you look at them carefully, you can see that their structure consists of six tops. But even more careful analysis shows that snowflakes in winter have the same structure, always symmetrical and with six tops. To what extent do crystallized structures contain information about the environment where they were created? The structure of snowflakes can be beautiful or shapeless. This indicates that the control sample (cloud in the atmosphere) where they occur has the same effect on them as the initial conditions. The initial conditions are solar activity, temperature, geophysical fields, humidity, etc. All this means that from the so-called. average ensemble, we can conclude that the structure of water drops, and then snowflakes, is approximately the same. Their mass is almost the same, and they move through the atmosphere at a similar speed. In the atmosphere, they continue to shape their structures and increase in volume. Even if they formed in different parts of the cloud, there are always a certain number of snowflakes in the same group that arose under almost the same conditions. And the answer to the question of what constitutes positive and negative information about snowflakes can be found in Emoto. Under laboratory conditions, negative information (earthquake, sound vibrations unfavorable for humans, etc.) does not form crystals, but positive information, just the opposite. It is very interesting to what extent one factor can form the same or similar structures of snowflakes. The highest density of water is observed at a temperature of 4 °C. It has been scientifically proven that the density of water decreases when hexagonal ice crystals begin to form as the temperature drops below zero. This is the result of the action of hydrogen bonds between water molecules.

What is the reason for this structuring? Crystals are solids, and their constituent atoms, molecules or ions are arranged in a regular, repeating structure, in three spatial dimensions. The structure of water crystals is slightly different. According to Isaac, only 10% of the hydrogen bonds in ice are covalent, i.e. with fairly stable information. Hydrogen bonds between the oxygen of one water molecule and the hydrogen of another are most sensitive to external influences. The spectrum of water during the formation of crystals is relatively different in time. According to the effect of discrete evaporation of a water drop proved by Antonov and Yuskeseliyev and its dependence on the energy states of hydrogen bonds, we can look for an answer about the structuring of crystals. Each part of the spectrum depends on the surface tension of the water droplets. There are six peaks in the spectrum, which indicate the ramifications of the snowflake.

Obviously, in Emoto's experiments, the initial "control" sample has an effect on the appearance of the crystals. This means that after exposure to a certain factor, the formation of such crystals can be expected. It is almost impossible to get identical crystals. When testing the effect of the word "love" on water, Emoto does not clearly indicate whether this experiment was carried out with different samples.

Doubly blind experiments are needed to test whether the Emoto technique differentiates sufficiently. Isaac's proof that 10% of water molecules form covalent bonds after freezing shows us that water uses this information when it freezes. Emoto's achievement, even without double-blind experiments, remains quite important in relation to the informational properties of water.

Natural snowflake, Wilson Bentley, 1925

Emoto snowflake obtained from natural water

One snowflake is natural, and the other is created by Emoto, indicating that the diversity in the water spectrum is not limitless.

Earthquake, Sofia, 4.0 Richter scale, November 15, 2008,
Dr. Ignatov, 2008©, Prof. Antonov's device ©

This figure indicates the difference between the control sample and those taken on other days. Water molecules break the most energetic hydrogen bonds in water, as well as two peaks in the spectrum during a natural phenomenon. The study was carried out using the Antonov device. The biophysical result shows a decrease in the vitality of the body during an earthquake. During an earthquake, water cannot change its structure in the snowflakes in Emoto's lab. There is evidence of a change in the electrical conductivity of water during an earthquake.

In 1963, Tanzanian schoolboy Erasto Mpemba noticed that hot water freezes faster than cold water. This phenomenon is called the Mpemba effect. Although the unique property of water was noticed much earlier by Aristotle, Francis Bacon and Rene Descartes. The phenomenon has been proven many times over by a number of independent experiments. Water has another strange property. In my opinion, the explanation for this is as follows: the differential nonequilibrium energy spectrum (DNES) of boiled water has a lower average energy of hydrogen bonds between water molecules than a sample taken at room temperature This means that boiled water needs less energy in order to begin to structure crystals and freeze.

The key to the structure of ice and its properties lies in the structure of its crystal. Crystals of all modifications of ice are built from water molecules H 2 O, connected by hydrogen bonds into three-dimensional mesh frames with a certain arrangement of hydrogen bonds. The water molecule can be simply imagined as a tetrahedron (pyramid with a triangular base). In its center there is an oxygen atom, which is in a state of sp 3 hybridization, and in two vertices there is a hydrogen atom, one of the 1s electrons of which is involved in the formation of a covalent H-O bond with oxygen. The two remaining vertices are occupied by pairs of unpaired oxygen electrons that do not participate in the formation of intramolecular bonds, therefore they are called lone. The spatial shape of the H 2 O molecule is explained by the mutual repulsion of hydrogen atoms and lone electron pairs of the central oxygen atom.

The hydrogen bond is important in the chemistry of intermolecular interactions and is driven by weak electrostatic forces and donor-acceptor interactions. It occurs when the electron-deficient hydrogen atom of one water molecule interacts with the lone electron pair of the oxygen atom of the neighboring water molecule (О-Н…О). A distinctive feature of the hydrogen bond is the relatively low strength; it is 5-10 times weaker than a chemical covalent bond. In terms of energy, a hydrogen bond occupies an intermediate position between a chemical bond and van der Waals interactions that hold molecules in a solid or liquid phase. Each water molecule in an ice crystal can simultaneously form four hydrogen bonds with other neighboring molecules at strictly defined angles equal to 109 ° 47 "directed to the vertices of the tetrahedron, which do not allow the formation of a dense structure when water freezes (Fig. 3). In ice structures I, Ic, VII and VIII this tetrahedron is regular. In the structures of ice II, III, V and VI, the tetrahedra are noticeably distorted. In the structures of ice VI, VII and VIII, two mutually crossing systems of hydrogen bonds can be distinguished. This invisible framework of hydrogen bonds arranges water molecules in the form of a grid, the structure resembling a hexagonal honeycomb with hollow internal channels.If the ice is heated, the grid structure is destroyed: water molecules begin to fall into the voids of the grid, leading to a denser structure of the liquid - this explains why water is heavier than ice.

Rice. 3. The formation of a hydrogen bond between four H 2 O molecules (red balls indicate central oxygen atoms, white balls indicate hydrogen atoms)

The specificity of hydrogen bonds and intermolecular interactions, characteristic of the structure of ice, is preserved in melt water, since only 15% of all hydrogen bonds are destroyed during the melting of an ice crystal. Therefore, the bond inherent in ice between each water molecule and its four neighbors ("short range order") is not violated, although the oxygen framework lattice is more diffuse. Hydrogen bonds can also be retained when water boils. Hydrogen bonds are absent only in water vapor.

Ice, which forms at atmospheric pressure and melts at 0 ° C, is the most familiar, but still not fully understood substance. Much in its structure and properties looks unusual. At the nodes of the crystal lattice of ice, the oxygen atoms of the tetrahedra of water molecules are arranged in an orderly manner, forming regular hexagons, like a hexagonal honeycomb, and hydrogen atoms occupy various positions on the hydrogen bonds connecting the oxygen atoms (Fig. 4). Therefore, there are six equivalent orientations of water molecules relative to their neighbors. Some of them are excluded, since the presence of two protons on the same hydrogen bond at the same time is unlikely, but there remains a sufficient uncertainty in the orientation of water molecules. This behavior of atoms is atypical, since in a solid matter all atoms obey the same law: either they are atoms arranged in an orderly manner, and then it is a crystal, or randomly, and then it is an amorphous substance. Such an unusual structure can be realized in most modifications of ice - Ih, III, V, VI, and VII (and, apparently, in Ic) (Table 3), and in the structure of ice II, VIII, and IX, water molecules are orientationally ordered. According to J. Bernal, ice is crystalline in relation to oxygen atoms and glassy in relation to hydrogen atoms.

Rice. 4. Structure of ice of natural hexagonal configuration I h

Under other conditions, for example, in space at high pressures and low temperatures, ice crystallizes differently, forming other crystal lattices and modifications (cubic, trigonal, tetragonal, monoclinic, etc.), each of which has its own structure and crystal lattice (Table 3). ). The structures of ice of various modifications were calculated by Russian researchers, Doctor of Chemical Sciences. G.G. Malenkov and Ph.D. E.A. Zheligovskaya from the Institute of Physical Chemistry and Electrochemistry. A.N. Frumkin of the Russian Academy of Sciences. Ice modifications II, III and V remain for a long time at atmospheric pressure if the temperature does not exceed -170 °C (Fig. 5). When cooled to approximately -150 ° C, natural ice turns into cubic ice Ic, consisting of cubes and octahedrons a few nanometers in size. Ice I c sometimes also appears when water freezes in capillaries, which is apparently facilitated by the interaction of water with the wall material and the repetition of its structure. If the temperature is slightly higher than -110 0 C, crystals of denser and heavier glassy amorphous ice with a density of 0.93 g/cm 3 are formed on the metal substrate. Both of these forms of ice can spontaneously transform into hexagonal ice, and the faster, the higher the temperature.

Tab. 3. Some modifications of ice and their physical parameters.

Modification

Crystal structure

Hydrogen bond lengths, Å

H-O-H angles in tetrahedra, 0

Hexagonal

cubic

Trigonal

tetragonal

Monoclinic

tetragonal

cubic

cubic

tetragonal

Note. 1 Å = 10 -10 m

Rice. 5. State diagram of crystalline ices of various modifications.

There are also high-pressure ices - II and III of trigonal and tetragonal modifications, formed from hollow acres formed by hexagonal corrugated elements shifted relative to each other by one third (Fig. 6 and Fig. 7). These ices are stabilized in the presence of the noble gases helium and argon. In the structure of ice V of the monoclinic modification, the angles between neighboring oxygen atoms range from 860 to 132°, which is very different from the bond angle in the water molecule, which is 105°47'. Ice VI of the tetragonal modification consists of two frames inserted into each other, between which there are no hydrogen bonds, as a result of which a body-centered crystal lattice is formed (Fig. 8). The structure of ice VI is based on hexamers - blocks of six water molecules. Their configuration exactly repeats the structure of a stable water cluster, which is given by the calculations. Ices VII and VIII of the cubic modification, which are low-temperature ordered forms of ice VII, have a similar structure with frameworks of ice I inserted into each other. With a subsequent increase in pressure, the distance between the oxygen atoms in the crystal lattice of ices VII and VIII will decrease, as a result, the structure of ice X is formed, in which the oxygen atoms are arranged in a regular lattice, and the protons are ordered.

Rice. 7. Ice of III configuration.

Ice XI is formed by deep cooling of ice I h with the addition of alkali below 72 K at normal pressure. Under these conditions, hydroxyl crystal defects are formed, allowing the growing ice crystal to change its structure. Ice XI has a rhombic crystal lattice with an ordered arrangement of protons and is formed at once in many crystallization centers near the hydroxyl defects of the crystal.

Rice. eight. Ice VI configuration.

Among the ices, there are also metastable forms IV and XII, whose lifetimes are seconds, which have the most beautiful structure (Fig. 9 and Fig. 10). To obtain metastable ice, it is necessary to compress ice I h to a pressure of 1.8 GPa at liquid nitrogen temperature. These ices form much more easily and are especially stable when supercooled heavy water is subjected to pressure. Another metastable modification, ice IX, is formed upon supercooling of ice III and is essentially its low-temperature form.

Rice. nine. Ice IV-configuration.

Rice. ten. Ice XII configuration.

The last two modifications of ice - with monoclinic XIII and rhombic configuration XIV were discovered by scientists from Oxford (Great Britain) quite recently - in 2006. The assumption that ice crystals with monoclinic and rhombic lattices should exist was difficult to confirm: the viscosity of water at a temperature of -160 ° C is very high, and it is difficult for molecules of pure supercooled water to come together in such an amount that a crystal nucleus is formed. This was achieved with the help of a catalyst - hydrochloric acid, which increased the mobility of water molecules at low temperatures. On Earth, such modifications of ice cannot form, but they can exist in space on cooled planets and frozen satellites and comets. Thus, the calculation of the density and heat fluxes from the surface of the satellites of Jupiter and Saturn allows us to assert that Ganymede and Callisto should have an ice shell in which ices I, III, V and VI alternate. At Titan, ice forms not a crust, but a mantle, the inner layer of which consists of ice VI, other high-pressure ices and clathrate hydrates, and ice I h is located on top.

Rice. eleven. Variety and shape of snowflakes in nature

High in the Earth's atmosphere at low temperatures, water crystallizes from tetrahedra, forming hexagonal ice I h . The center of formation of ice crystals is solid dust particles, which are lifted into the upper atmosphere by the wind. Around this embryonic microcrystal of ice, needles formed by individual water molecules grow in six symmetrical directions, on which lateral processes - dendrites grow. The temperature and humidity of the air around the snowflake are the same, so initially it is symmetrical in shape. As snowflakes form, they gradually sink into the lower layers of the atmosphere, where temperatures are higher. Here melting occurs and their ideal geometric shape is distorted, forming a variety of snowflakes (Fig. 11).

With further melting, the hexagonal structure of ice is destroyed and a mixture of cyclic associates of clusters is formed, as well as from tri-, tetra-, penta-, hexamers of water (Fig. 12) and free water molecules. The study of the structure of the resulting clusters is often significantly difficult, since, according to modern data, water is a mixture of various neutral clusters (H 2 O) n and their charged cluster ions [H 2 O] + n and [H 2 O] - n, which are in dynamic equilibrium between with a lifetime of 10 -11 -10 -12 seconds.

Rice. 12. Possible water clusters (a-h) of composition (H 2 O) n, where n = 5-20.

Clusters are able to interact with each other due to the protruding faces of hydrogen bonds, forming more complex polyhedral structures, such as hexahedron, octahedron, icosahedron, and dodecahedron. Thus, the structure of water is associated with the so-called Platonic solids (tetrahedron, hexahedron, octahedron, icosahedron and dodecahedron), named after the ancient Greek philosopher and geometer Plato who discovered them, the shape of which is determined by the golden ratio (Fig. 13).

Rice. thirteen. Platonic solids, the geometric shape of which is determined by the golden ratio.

The number of vertices (B), faces (G) and edges (P) in any spatial polyhedron is described by the relation:

C + D = P + 2

The ratio of the number of vertices (B) of a regular polyhedron to the number of edges (P) of one of its faces is equal to the ratio of the number of faces (G) of the same polyhedron to the number of edges (P) emerging from one of its vertices. For a tetrahedron, this ratio is 4:3, for a hexahedron (6 faces) and an octahedron (8 faces) - 2:1, and for a dodecahedron (12 faces) and an icosahedron (20 faces) - 4:1.

The structures of polyhedral water clusters calculated by Russian scientists were confirmed using modern methods of analysis: proton magnetic resonance spectroscopy, femtosecond laser spectroscopy, X-ray and neutron diffraction on water crystals. The discovery of water clusters and the ability of water to store information are the two most important discoveries of the 21st millennium. This clearly proves that nature is characterized by symmetry in the form of precise geometric shapes and proportions, characteristic of ice crystals.

LITERATURE.

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6. Kulsky L. A., Dal V. V., Lenchina L. G. Water is familiar and mysterious. - Kyiv, Rodyansk school, 1982, p. 62-64.

7. G. N. Zatsepina, Structure and properties of water. - Moscow, ed. Moscow State University, 1974, p. 125.

8. Antonchenko V. Ya., Davydov N. S., Ilyin V. V. Fundamentals of water physics - Kyiv, Naukova Dumka, 1991, p. 167.

9. Simonite T. DNA-like ice "seen" inside carbon nanotubes // New Scientist, V. 12, 2006.

10. Emoto M. Messages of water. Secret codes of ice crystals. - Sofia, 2006. p. 96.

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14. Hobza P., Zahradnik R. Intermolecular complexes: The role of van der Waals systems in physical chemistry and biodisciplines. - Moscow, Mir, 1989, p. 34-36.

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The three-dimensional state of liquid water is difficult to study, but much has been learned by analyzing the structure of ice crystals. Four neighboring hydrogen-interacting oxygen atoms occupy the vertices of a tetrahedron (tetra = four, hedron = plane). The average energy required to break such a bond in ice is estimated at 23 kJ/mol -1 .

The ability of water molecules to form a given number of hydrogen chains, as well as the indicated strength, creates an unusually high melting point. When it melts, it is held by liquid water, the structure of which is irregular. Most of the hydrogen bonds are distorted. To destroy the crystal lattice of ice with a hydrogen bond, a large mass of energy in the form of heat is required.

Features of the appearance of ice (Ih)

Many of the inhabitants are wondering what kind of crystal lattice ice has. It should be noted that the density of most substances increases during freezing, when molecular movements slow down and densely packed crystals form. The density of water also increases as it cools to a maximum at 4°C (277K). Then, when the temperature drops below this value, it expands.

This increase is due to the formation of an open, hydrogen-bonded ice crystal with its lattice and lower density, in which each water molecule is rigidly bound by the above element and four other values, while moving fast enough to have more mass. Since this action occurs, the liquid freezes from top to bottom. This has important biological results, as a result of which the layer of ice on the pond insulates living beings away from extreme cold. In addition, two additional properties of water are related to its hydrogen characteristics: specific heat capacity and evaporation.

Detailed description of structures

The first criterion is the amount required to raise the temperature of 1 gram of a substance by 1°C. Raising the degrees of water requires a relatively large amount of heat because each molecule is involved in numerous hydrogen bonds that must be broken in order for the kinetic energy to increase. By the way, the abundance of H 2 O in the cells and tissues of all large multicellular organisms means that temperature fluctuations inside the cells are minimized. This feature is critical because the rate of most biochemical reactions is sensitive.

Also significantly higher than many other liquids. A large amount of heat is required to convert this body into a gas, because the hydrogen bonds must be broken in order for the water molecules to dislocate from each other and enter the said phase. Changeable bodies are permanent dipoles and can interact with other similar compounds and those that ionize and dissolve.

Other substances mentioned above can come into contact only if polarity is present. It is this compound that is involved in the structure of these elements. In addition, it can align around these particles formed from electrolytes, so that the negative oxygen atoms of the water molecules are oriented to the cations, and the positive ions and hydrogen atoms are oriented to the anions.

In are formed, as a rule, molecular crystal lattices and atomic. That is, if iodine is constructed in such a way that I 2 is present in it, then in solid carbon dioxide, that is, in dry ice, CO 2 molecules are located at the nodes of the crystal lattice. When interacting with similar substances, ice has an ionic crystal lattice. Graphite, for example, having an atomic structure based on carbon, is not able to change it, just like diamond.

What happens when a crystal of table salt dissolves in water is that the polar molecules are attracted to the charged elements in the crystal, which leads to the formation of similar particles of sodium and chloride on its surface, as a result of which these bodies dislocate from each other, and it begins to dissolve. From here it can be observed that ice has a crystal lattice with ionic bonding. Each dissolved Na + attracts the negative ends of several water molecules, while each dissolved Cl - attracts the positive ends. The shell surrounding each ion is called the escape sphere and usually contains several layers of solvent particles.

Variables or an ion surrounded by elements are said to be sulfated. When the solvent is water, such particles are hydrated. Thus, any polar molecule tends to be solvated by the elements of the liquid body. In dry ice, the type of crystal lattice forms atomic bonds in the state of aggregation, which are unchanged. Another thing is crystalline ice (frozen water). Ionic organic compounds such as carboxylases and protonated amines must be soluble in hydroxyl and carbonyl groups. The particles contained in such structures move between molecules, and their polar systems form hydrogen bonds with this body.

Of course, the number of the last mentioned groups in the molecule affects its solubility, which also depends on the reaction of various structures in the element: for example, one-, two- and three-carbon alcohols are miscible with water, but larger hydrocarbons with single hydroxyl compounds are much less diluted in liquids.

The hexagonal Ih is similar in shape to the atomic crystal lattice. For ice and all natural snow on Earth, it looks exactly like this. This is evidenced by the symmetry of the crystal lattice of ice, grown from water vapor (that is, snowflakes). It is in space group P 63/mm from 194; D 6h, Laue class 6/mm; similar to β-, which has a multiple of 6 helical axis (rotation around in addition to shift along it). It has a rather open low density structure where the efficiency is low (~1/3) compared to simple cubic (~1/2) or face centered cubic (~3/4) structures.

Compared to ordinary ice, the crystal lattice of dry ice, bound by CO 2 molecules, is static and changes only when atoms decay.

Description of lattices and their constituent elements

Crystals can be thought of as crystalline models consisting of sheets stacked on top of each other. The hydrogen bond is ordered, while in reality it is random, since protons can move between water (ice) molecules at temperatures above about 5 K. Indeed, it is likely that protons behave like a quantum fluid in a constant tunneling flow. This is enhanced by the scattering of neutrons, showing their scattering density halfway between the oxygen atoms, indicating localization and concerted motion. Here there is a similarity of ice with an atomic, molecular crystal lattice.

Molecules have a stepped arrangement of the hydrogen chain with respect to their three neighbors in the plane. The fourth element has an eclipsed hydrogen bond arrangement. There is a slight deviation from perfect hexagonal symmetry, like 0.3% shorter in the direction of this chain. All molecules experience the same molecular environments. Inside each "box" there is enough space to hold particles of interstitial water. Although not generally considered, they have recently been effectively detected by neutron diffraction of the powdery crystal lattice of ice.

Changing Substances

The hexagonal body has triple points with liquid and gaseous water 0.01 ° C, 612 Pa, solid elements - three -21.985 ° C, 209.9 MPa, eleven and two -199.8 ° C, 70 MPa, and -34 .7 °C, 212.9 MPa. The dielectric constant of hexagonal ice is 97.5.

The melting curve of this element is given by MPa. The equations of state are available, in addition to them, some simple inequalities relating the change in physical properties to the temperature of hexagonal ice and its aqueous suspensions. Hardness fluctuates with degrees rising from or below gypsum (≤2) at 0°C to feldspar (6 at -80°C, an abnormally large change in absolute hardness (>24 times).

The hexagonal crystal lattice of ice forms hexagonal plates and columns, where the upper and lower faces are the basal planes (0 0 0 1) with an enthalpy of 5.57 μJ cm -2, and the other equivalent side faces are called parts of the prism (1 0 -1 0) with 5.94 μJ cm -2 . Secondary surfaces (1 1 -2 0) with 6.90 μJ ˣ cm -2 can be formed along the planes formed by the sides of the structures.

A similar structure shows an anomalous decrease in thermal conductivity with increasing pressure (as well as cubic and amorphous ice of low density), but differs from most crystals. This is due to a change in the hydrogen bond, which reduces the transverse speed of sound in the crystal lattice of ice and water.

There are methods describing how to prepare large crystal samples and any desired ice surface. It is assumed that the hydrogen bond on the surface of the hexagonal body under study will be more ordered than inside the bulk system. Variational spectroscopy with phase-lattice frequency generation has shown that there is a structural asymmetry between the two upper layers (L1 and L2) in the subsurface HO chain of the basal surface of hexagonal ice. The adopted hydrogen bonds in the upper layers of the hexagons (L1 O ··· HO L2) are stronger than those accepted in the second layer to the upper accumulation (L1 OH ··· O L2). Interactive structures of hexagonal ice are available.

Development features

The minimum number of water molecules required for ice nucleation is approximately 275 ± 25, as for a complete icosahedral cluster of 280. Formation occurs at a factor of 10 10 at the air-water interface, not in bulk water. The growth of ice crystals depends on different growth rates of different energies. Water must be protected from freezing when cryopreserving biological specimens, food, and organs.

This is usually achieved by fast cooling rates, the use of small samples and a cryoconservator, and increased pressure to nucleate ice and prevent cell damage. The free energy of ice/liquid increases from ~30 mJ/m2 at atmospheric pressure to 40 mJ/m -2 at 200 MPa, indicating the reason why this effect occurs.

Alternatively, they can grow faster from prism surfaces (S2), on the randomly disturbed surface of quick-frozen or agitated lakes. The growth from the faces (1 1 -2 0) is at least the same, but turns them into prism bases. The data on the development of the ice crystal have been fully investigated. The relative growth rates of elements of different faces depend on the ability to form a large degree of joint hydration. The temperature (low) of the surrounding water determines the degree of branching in the ice crystal. Particle growth is limited by the diffusion rate at a low degree of supercooling, i.e.<2 ° C, что приводит к большему их количеству.

But limited by developmental kinetics at higher levels of depression >4°C, resulting in needle-like growth. This shape is similar to dry ice (has a crystal lattice with a hexagonal structure), different surface development characteristics, and the temperature of the surrounding (supercooled) water that lies behind the flat snowflake shapes.

The formation of ice in the atmosphere profoundly influences the formation and properties of clouds. Feldspars, found in desert dust that enters the atmosphere in millions of tons per year, are important formers. Computer modeling has shown that this is due to the nucleation of prismatic ice crystal planes on high-energy surface planes.

Some other elements and lattices

Solutes (with the exception of very small helium and hydrogen, which may enter interstices) cannot be incorporated into the Ih structure at atmospheric pressure, but are displaced to the surface or amorphous layer between particles of the microcrystalline body. There are some other elements at the lattice sites of dry ice: chaotropic ions such as NH 4 + and Cl - , which are included in the easier freezing of the liquid than other cosmotropic ones, such as Na + and SO 4 2- , so their removal is impossible, due to the fact that they form a thin film of the remaining liquid between the crystals. This can lead to electrical charging of the surface due to surface water dissociation balancing the remaining charges (which can also lead to magnetic radiation) and a change in the pH of the residual liquid films, for example, NH 4 2 SO 4 becomes more acidic and NaCl becomes more basic.

They are perpendicular to the faces of the ice crystal lattice, showing the attached next layer (with O-black atoms). They are characterized by a slowly growing basal surface (0 0 0 1), where only isolated water molecules are attached. A rapidly growing (1 0 -1 0) surface of a prism where pairs of newly attached particles can bond with each other with hydrogen (one hydrogen bond/two molecules of an element). The fastest growing face (1 1 -2 0) (secondary prismatic), where chains of newly attached particles can interact with each other by hydrogen bonding. One of its chain/element molecule is a form that forms ridges that divide and encourage the transformation into two sides of the prism.

Zero point entropy

k Bˣ Ln ( N

Scientists and their works in this area

Can be defined as S 0 = k Bˣ Ln ( N E0), where k B is the Boltzmann constant, N E is the number of configurations at the energy E, and E0 is the lowest energy. This value for the entropy of hexagonal ice at zero kelvin does not violate the third law of thermodynamics "The entropy of an ideal crystal at absolute zero is exactly zero", since these elements and particles are not ideal, have disordered hydrogen bonding.

In this body, the hydrogen bond is random and rapidly changing. These structures are not exactly equal in energy, but extend to a very large number of energetically close states, obey the "rules of ice". Zero point entropy is the disorder that would remain even if the material could be cooled to absolute zero (0 K = -273.15 °C). Generates experimental confusion for hexagonal ice 3.41 (± 0.2) ˣ mol -1 ˣ K -1 . Theoretically, it would be possible to calculate the zero entropy of known ice crystals with much greater accuracy (neglecting defects and energy level spread) than to determine it experimentally.

Although the order of protons in bulk ice is not ordered, the surface probably prefers the order of these particles in the form of bands of hanging H-atoms and O-single pairs (zero entropy with ordered hydrogen bonds). The disorder of the zero point ZPE, J ˣ mol -1 ˣ K -1 and others is found. From all of the above, it is clear and understandable what types of crystal lattices are characteristic of ice.

If there are non-polar molecules of some substance at the nodes of the crystal lattice (like iodine I 2, oxygen About 2 or nitrogen N 2), then they do not experience any electrical "sympathy" for each other. In other words, their molecules should not be attracted by electrostatic forces. And yet something keeps them together. What exactly?

It turns out that in the solid state, these molecules come so close to each other that instantaneous (though very weak) reactions begin in their electron clouds. bias- condensation and rarefaction of electron clouds. Instead of non-polar particles, "instantaneous dipoles" appear, which can already be attracted to each other electrostatically. However, this attraction is very weak. Therefore, the crystal lattices of non-polar substances are fragile and exist only at very low temperatures, in "cosmic" cold.

Astronomers have indeed discovered celestial bodies - comets, asteroids, even entire planets, consisting of frozen nitrogen, oxygen and other substances that, under ordinary terrestrial conditions, exist in the form of gases and become solid in interplanetary space.

	Many simple and complex substances with molecular the crystal lattice is well known to everyone. This is, for example, a crystalline iodine I 2:
This is how the crystal lattice is built iodine: it consists of iodine molecules (each of them contains two iodine atoms).
	And these molecules are rather loosely bound together. That is why crystalline iodine is so volatile and even with the slightest heating it evaporates, turning into gaseous iodine - a beautiful purple vapor.

Which common substances molecular crystal lattice?

• Crystalline water (ice) consists of polar molecules water H2O.
• The "dry ice" crystals used to cool ice cream are also molecular crystals. carbon dioxide CO2.
• Another example is sugar, which forms crystals from molecules sucrose.

When there are molecules of a substance at the nodes of the crystal lattice, the bonds between them are not very strong, even if these molecules are polar.
Therefore, in order to melt such crystals or evaporate substances with a molecular crystal structure, it is not necessary to heat them to a red heat.
Already at 0 °C, the crystal structure ice breaks down and becomes water. And "dry ice" does not melt at normal pressure, but immediately turns into gaseous carbon dioxide- exalted.

Another thing is substances with atomic a crystal lattice, where each atom is connected with its neighbors by very strong covalent bonds, and the entire crystal as a whole, if desired, can be considered a huge molecule.

For an example, consider diamond crystal, which is made up of atoms carbon.

	Atom carbon With, which contains two unpaired R -electron turns into an atom carbon WITH*, where all four electrons of the outer valence level are located in orbits one by one and able to form chemical bonds. Chemists call such an atom " excited".
In this case, there are as many as four chemical bonds, and all very durable. not without reason diamond - the hardest substance in nature and since time immemorial is considered the king of all gems and precious stones. And its very name means in Greek "indestructible."
	From faceted crystals diamond diamonds are obtained, which adorn expensive jewelry

The most beautiful diamonds found by people have their own, sometimes tragic, history. Read >>>

But diamond goes not only on decorations. Its crystals are used in tools for processing the hardest materials, drilling in rocks, cutting and cutting glass and crystal.

Crystal lattice of diamond (left) and graphite (right)

Graphite the same composition carbon, but its crystal lattice structure is not the same as that of diamond. AT graphite carbon atoms are arranged in layers, within which the connection of carbon atoms is similar to a honeycomb. These layers are much weaker bonded than the carbon atoms in each layer. So graphite easily stratified into scales, and they can write. It is used for the manufacture of pencils, as well as a dry lubricant suitable for machine parts operating at high temperatures. Besides, graphite conducts electricity well, and electrodes are made from it.

Can an inexpensive graphite turn into precious diamond? It is possible, but this will require unthinkably high pressure (several thousand atmospheres) and high temperature (one and a half thousand degrees).
Much easier to mess up diamond: you just need to heat it without air access to 1500 ° C, and the crystal structure diamond turn into a less ordered structure graphite.

Crystal structure of ice: water molecules are connected in regular hexagons Crystal lattice of ice: Water molecules H 2 O (black balls) in its nodes are arranged so that each has four neighbors. The water molecule (center) is hydrogen bonded to the four nearest neighboring molecules. Ice is a crystalline modification of water. According to the latest data, ice has 14 structural modifications. Among them there are both crystalline (they are the majority) and amorphous modifications, but they all differ from each other in the mutual arrangement of water molecules and properties. True, everything, except for the usual ice that crystallizes in the hexagonal syngony, is formed under exotic conditions at very low temperatures and high pressures, when the angles of hydrogen bonds in the water molecule change and systems other than hexagonal are formed. Such conditions are reminiscent of cosmic conditions and are not found on Earth. For example, at temperatures below -110 °C, water vapor precipitates on a metal plate in the form of octahedrons and cubes a few nanometers in size, this is the so-called cubic ice. If the temperature is slightly above –110 °C, and the vapor concentration is very low, a layer of exceptionally dense amorphous ice forms on the plate. The most unusual property of ice is the amazing variety of external manifestations. With the same crystal structure, it can look completely different, taking the form of transparent hailstones and icicles, fluffy snow flakes, a dense shiny crust of ice, or giant glacial masses.

A snowflake is a single crystal of ice - a kind of hexagonal crystal, but grown quickly, in non-equilibrium conditions. Scientists have been wrestling with the secret of their beauty and endless variety for centuries. The life of a snowflake begins with the formation of crystalline ice nuclei in a cloud of water vapor as the temperature drops. The center of crystallization can be dust particles, any solid particles or even ions, but in any case, these ice floes smaller than a tenth of a millimeter already have a hexagonal crystal lattice. Water vapor, condensing on the surface of these nuclei, first forms a tiny hexagonal prism, from the six corners of which we begin grow identical ice needles lateral processes, because the temperature and humidity around the embryo are also the same. On them, in turn, grow, like on a tree, lateral branches of the branch. Such crystals are called dendrites, that is, similar to a tree. Moving up and down in the cloud, the snowflake enters conditions with different temperatures and water vapor concentrations. Its shape changes, to the last obeying the laws of hexagonal symmetry. So snowflakes become different. Until now, it has not been possible to find two identical snowflakes among the snowflakes.

The color of ice depends on its age and can be used to evaluate its strength. Ocean ice is white in the first year of its life because it is saturated with air bubbles, from the walls of which light is reflected immediately, before being absorbed. In summer, the ice surface melts, loses its strength, and under the weight of new layers lying on top, air bubbles shrink and disappear completely. The light inside the ice travels a greater distance than before and emerges as a bluish-green hue. Blue ice is older, denser and stronger than white “foamy” ice saturated with air. Polar explorers know this and choose reliable blue and green ice floes for their floating bases, scientific stations and ice airfields. There are black icebergs. The first press report about them appeared in 1773. The black color of icebergs is caused by the activity of volcanoes - the ice is covered with a thick layer of volcanic dust, which is not washed away even by sea water. The ice is not equally cold. There is very cold ice, with a temperature of about minus 60 degrees, this is the ice of some Antarctic glaciers. The ice of the Greenland glaciers is much warmer. Its temperature is approximately minus 28 degrees. Quite "warm ice" (with a temperature of about 0 degrees) lie on the tops of the Alps and the Scandinavian mountains.

The density of water is maximum at +4 C and is equal to 1 g/ml, it decreases with decreasing temperature. When water crystallizes, the density decreases sharply, for ice it is equal to 0.91 g / cm 3. Due to this, ice is lighter than water and when water bodies freeze, ice accumulates on top, and denser water with a temperature of 4 ̊ C appears at the bottom of water bodies. Poor thermal conductivity of ice and The snow cover covering it protects water bodies from freezing to the bottom and thereby creates conditions for the life of the inhabitants of water bodies in winter.

Glaciers, ice sheets, permafrost, seasonal snow cover significantly affect the climate of large regions and the planet as a whole: even those who have never seen snow feel the breath of its masses accumulated at the Earth's poles, for example, in the form of long-term level fluctuations World Ocean. Ice is so important for the appearance of our planet and the comfortable habitation of living beings on it that scientists have assigned a special environment for it - the cryosphere, which extends its possessions high into the atmosphere and deep into the earth's crust. Natural ice is usually much cleaner than water because the solubility of substances (except NH4F) in ice is extremely low. The total ice reserves on Earth are about 30 million km 3. Most of the ice is concentrated in Antarctica, where the thickness of its layer reaches 4 km.