The structure of ice molecules. How are water molecules and ice molecules different? Captions for illustrations
Introduction
1. The structure of water molecules
2. Structure of water in its three states of aggregation
3. Types of water
4. Anomalous properties of water
5. Phase transformations and state diagram of water
6. Models of the structure of water and ice
7. Aggregate types of ice
Conclusion
Bibliography
Introduction
Water is the most important substance on Earth without which no living organism can exist and no biological, chemical reactions or technological processes can occur.
Water (hydrogen oxide) is an odorless, tasteless and colorless liquid (bluish in thick layers); H 2 O, mol. m. 18.016, the simplest stable connection. hydrogen with oxygen.
Water is one of the most common substances in nature. It covers about 3/4 of the entire earth's surface, forming the basis of oceans, seas, lakes, rivers, pound waters and swamps. A large amount of water is also found in the atmosphere. Plants and living organisms contain 50-96% water.
Water molecules have been discovered in interstellar space. Water is part of comets, most planets in the solar system and their satellites. The amount of water on the Earth's surface is estimated at 1.39 * 10 18 tons, most of it is contained in the seas and oceans. The amount of fresh water available for use in rivers, lakes, swamps and reservoirs is 2 * 10 4 tons. The mass of glaciers in Antarctica, Antarctica and high mountain regions is 2.4 * 10 16 tons (the total mass of snow and ice distributed over the Earth's surface reaches approximately 2.5-3.010 16 tons, which is only 0.0004% of the mass of our entire planet.However, such an amount is enough to cover the entire surface of the Earth with a 53-meter layer, and if all this mass suddenly melted, having turned into water, the level of the World Ocean would have risen by about 64 meters compared to the current one.), there is approximately the same amount of groundwater, and only a small part of it is fresh. In the atmosphere there is approx. 1.3*10 13 tons of water. Water is part of many minerals and rocks (clay, gypsum, etc.), is present in the soil, and is an essential component of all living organisms.
Density of H 2 O = 1 g/cm3 (at 3.98 degrees), t pl. = 0 degrees, and t kip = 100 degrees. The heat capacity of water is 4.18 J/(g/K) Mr (H 2 O) = 18 and corresponds to its simplest formula. However, the molecular weight of liquid water, determined by studying its solutions in other solvents, turns out to be higher. This indicates that in liquid water there is an association of molecules, i.e., they are combined into more complex aggregates. Water is the only substance in nature that, under terrestrial conditions, exists in all three states of aggregation: Much water is in a gaseous state in the form of vapor in the atmosphere; it lies in the form of huge masses of snow and ice all year round on the tops of high mountains and in polar countries. In the bowels of the earth there is also water that saturates the soil and rocks
Climate depends on water. Geophysicists claim that the Earth would have cooled long ago and turned into a lifeless piece of stone if it were not for water. It has a very high heat capacity. When heated, it absorbs heat; cooling down, he gives it away. Earth's water both absorbs and returns a lot of heat and thereby “evens out” the climate. And what protects the Earth from the cosmic cold are those water molecules that are scattered in the atmosphere - in clouds and in the form of vapor... You cannot do without water - this is the most important substance on Earth.
Water is a familiar and unusual substance. Famous Soviet scientist
Academician I.V. Petryanov called his popular science book about water “the most extraordinary substance in the world.” And “Entertaining Physiology,” written by Doctor of Biological Sciences B.F. Sergeev, begins with a chapter about water - “The Substance that Created Our Planet.”
1. Structure of a water molecule
Of all common liquids, water is the most universal solvent, the liquid with the maximum values of surface tension, dielectric constant, heat of vaporization and the highest (after ammonia) heat of fusion. Unlike most substances, water expands when it freezes at low pressure.
These specific properties of water are associated with the special structure of its molecule. The chemical formula of water, H 2 0, is deceptively simple. In a water molecule, the nuclei of hydrogen atoms are located asymmetrically with respect to the nucleus of the oxygen atom and electrons. If the oxygen atom is at the center of the tetrahedron, the centers of mass of the two hydrogen atoms will be in the corners of the tetrahedron, and the centers of charge of the two pairs of electrons will occupy the other two corners (Fig. 1.1). Thus, four electrons are located at the greatest possible distance both from the nucleus of the oxygen atom and from the nuclei of the hydrogen atoms, at which they are still attracted by the nucleus of the oxygen atom. The other six electrons of the water molecule are arranged as follows: four electrons are in a position that provides a chemical bond between the nuclei of the oxygen and hydrogen atoms, and the other two are located near the nucleus of the oxygen atom.
The asymmetric arrangement of the atoms of a water molecule causes an uneven distribution of electrical charges in it, which makes the water molecule polar. This structure of the water molecule causes the attraction of water molecules to each other as a result of the formation of hydrogen bonds between them. The arrangement of hydrogen and oxygen atoms inside the formed aggregates of water molecules is similar to the arrangement of silicon and oxygen atoms in quartz. This applies to ice and, to a lesser extent, to liquid water, whose molecular aggregates are always in the stage of redistribution. When water cools, its molecules group into aggregates, which gradually increase in size and become more stable as the temperature approaches 4° C, when the water reaches its maximum density. At this temperature, water does not yet have a rigid structure and, along with long chains of its molecules, there are a large number of individual water molecules. With further cooling, the chains of water molecules grow due to the addition of free molecules to them, as a result of which the density of water decreases. When water turns into ice, all its molecules enter a more or less rigid structure in the form of open chains that form crystals.
Fig. 1.1 Structure of a water molecule
Mutual penetration of hydrogen and oxygen atoms. The nuclei of two hydrogen atoms and two pairs of electrons are located in the corners of the tetrahedron: in the center is the nucleus of an oxygen atom.
The high values of surface tension and heat of vaporization of water are explained by the fact that a relatively large expenditure of energy is required to separate a water molecule from a group of molecules. The tendency of water molecules to form hydrogen bonds and their polarity explain the unusually high solubility of water. Some compounds, such as sugars and alcohols, are held in solution by hydrogen bonds. Compounds that are highly ionized, such as sodium chloride, are held in solution because ions with opposite charges are neutralized by groups of oriented water molecules.
Another feature of the water molecule is that both hydrogen and oxygen atoms can have different masses with the same nuclear charge. Varieties of a chemical element with different atomic weights are called isotopes of that element. A water molecule is usually formed by hydrogen with atomic weight 1 (H 1) and oxygen with atomic weight 16 (O 16). More than 99% of water atoms belong to these isotopes. In addition, the following isotopes exist: H 2, H 3, O 14, O 15, O 17, O 18, O 19. Many of them accumulate in water as a result of its partial evaporation and due to their large mass. The isotopes H 3, O 14, O 15, O 19 are radioactive. The most common of them is tritium H 3, formed in the upper layers of the atmosphere under the influence of cosmic rays. This isotope has also accumulated as a result of nuclear explosions over the past few years. Based on these and other facts about isotopes, analysis of the isotopic composition of water can partially reveal the history of some natural waters. Thus, the content of heavy isotopes in surface waters indicates long-term evaporation of water, which occurs, for example, in the Dead Sea, the Great Salt Lake and other closed reservoirs. Elevated levels of tritium in groundwater could mean that these waters are of meteoric origin with a high circulation rate, because the half-life of this isotope is only 12.4 years. Unfortunately, isotope analysis is too expensive and for this reason cannot be widely used in studies of natural waters.
The water molecule H2O is built in the form of a triangle: the angle between the two oxygen-hydrogen bonds is 104 degrees. But since both hydrogen atoms are located on the same side of the oxygen, the electrical charges in it are dispersed. The water molecule is polar, which is the reason for the special interaction between its different molecules.
The hydrogen atoms in the H 2 O molecule, having a positive partial charge, interact with the electrons of the oxygen atoms of neighboring molecules. This chemical bond is called a hydrogen bond. It combines H 2 O molecules into unique polymers of a spatial structure; the plane in which the hydrogen bonds are located is perpendicular to the plane of the atoms of the same H 2 O molecule. The interaction between water molecules primarily explains the abnormally high temperatures of its melting and boiling. Additional energy must be supplied to loosen and then destroy hydrogen bonds. And this energy is very significant. This is why the heat capacity of water is so high.
Like most substances, water is made up of molecules, and the latter are made up of atoms.
Option #1.
1. Are ice and water molecules different from each other?
1) they are the same; 2) the ice molecule is colder; 3) the ice molecule is smaller;
4) the water molecule is smaller
2. What is diffusion?
Molecules of another; 3) chaotic movement of molecules of matter;
4) mixing substances
4. When a substance cools, the molecules move:
Kind of substance
5. The speed of movement of hydrogen molecules has increased. Wherein
Temperature …
No answer
6. If you pour water from a glass into a plate, then...
Shape and volume
7. In which water does diffusion occur faster?
Happening
8. In which substances does diffusion occur more slowly when od-
Under what conditions?
All substances
9. Molecules of a substance are located at large distances,
Are strongly attracted and oscillate around the equilibrium position
This substance...
1) gaseous; 2) liquid; 3) hard; 4) such a substance does not exist
Option number 2.
1. Are the molecules of ice and water vapor different from each other?
1) the ice molecule is colder; 2) they are the same; 3) ice molecule
Less; 4) the ice molecule is larger
2. Diffusion is...
1) penetration of molecules of one substance into molecules of another;
2) penetration of molecules of one substance into the spaces between
Molecules of another; 3) chaotic movement of molecules of substances
Va; 4) mixing substances
3. Between the molecules of any substance there is:
1) mutual attraction; 2) mutual repulsion; 3) mutual
Attraction and repulsion; 4) different substances have different
4. When water is heated, molecules move:
1) at the same speed; 2) slower; 3) faster; 4) depends on
Kind of substance
5. The speed of movement of oxygen molecules has decreased. Wherein
Temperature …
1) has not changed; 2) decreased; 3) increased; 4) correct
No answer
6. If you pour water from a plate into a glass, then...
1) the shape and volume of water will change; 2) the shape will change, the volume will change
Stored; 3) the shape will remain the same, the volume will change; 4) will be preserved
Volume and shape
7. In which water does diffusion occur more slowly?
1) in cold; 2) hot; 3) the same; 4) diffusion in water is not
Happening
8. In which substances does diffusion occur faster at the same
What are your conditions?
1) in gaseous; 2) in liquid; 3) in solids; 4) the same in
All substances
9. Molecules of a substance are located at short distances, strongly
They attract and oscillate around the equilibrium position. This
Substance...
1) gaseous; 2) liquid; 3) hard; 4) there is no such substance
Exists
V.V. Makhrova, GS(K)OU S(K)OSH (VII type) N 561, St. Petersburg
Properties of water
Why is water water?
Among the vast variety of substances, water with its physical and chemical properties occupies a very special, exceptional place. And this must be taken literally.
Almost all physical and chemical properties of water are exceptions in nature. It truly is the most amazing substance in the world. Water is amazing not only for the variety of isotopic forms of the molecule and not only for the hopes that are associated with it as an inexhaustible source of energy for the future. In addition, it is amazing for its very ordinary properties.
How is a water molecule built?
How one molecule of water is built is now known very precisely. It's built like this.
The relative positions of the nuclei of hydrogen and oxygen atoms and the distance between them have been well studied and measured. It turned out that the water molecule is nonlinear. Together with the electron shells of the atoms, a water molecule, if you look at it “from the side,” could be depicted like this:
that is, geometrically, the mutual arrangement of charges in a molecule can be depicted as a simple tetrahedron. All water molecules with any isotopic composition are built exactly the same.
How many water molecules are there in the ocean?
One. And this answer is not exactly a joke. Of course, anyone can, by looking at a reference book and finding out how much water there is in the World Ocean, easily calculate how many H2O molecules it contains. But such an answer will not be entirely correct. Water is a special substance. Due to their unique structure, individual molecules interact with each other. A special chemical bond arises due to the fact that each of the hydrogen atoms of one molecule attracts electrons of oxygen atoms in neighboring molecules. Due to this hydrogen bond, each water molecule becomes quite tightly bound to four other neighboring molecules, just as shown in the diagram. True, this diagram is too simplified - it is flat, otherwise it cannot be depicted in the figure. Let's imagine a slightly more accurate picture. To do this, you need to take into account that the plane in which hydrogen bonds are located (they are indicated by a dotted line) in a water molecule is directed perpendicular to the plane of location of the hydrogen atoms.
All individual H2O molecules in water turn out to be connected into a single continuous spatial network - into one giant molecule. Therefore, the assertion of some physical chemists that the entire ocean is one molecule is quite justified. But this statement should not be taken too literally. Although all water molecules in water are connected to each other by hydrogen bonds, they are at the same time in a very complex mobile equilibrium, preserving the individual properties of individual molecules and forming complex aggregates. This idea applies not only to water: a piece of diamond is also one molecule.
How is an ice molecule built?
There are no special ice molecules. The molecules of water, due to their remarkable structure, are connected to each other in a piece of ice so that each of them is connected and surrounded by four other molecules. This leads to the appearance of a very loose ice structure, in which a lot of free volume remains. The correct crystalline structure of ice is expressed in the amazing grace of snowflakes and the beauty of frosty patterns on frozen window panes.
How are water molecules built in water?
Unfortunately, this very important issue has not yet been sufficiently studied. The structure of molecules in liquid water is very complex. When ice melts, its network structure is partially preserved in the resulting water. The molecules in melt water consist of many simple molecules - aggregates that retain the properties of ice. As the temperature rises, some of them disintegrate and their sizes become smaller.
Mutual attraction leads to the fact that the average size of a complex water molecule in liquid water significantly exceeds the size of a single water molecule. This extraordinary molecular structure of water determines its extraordinary physicochemical properties.
What should the density of water be?
Isn't that a very strange question? Remember how the unit of mass was established - one gram. This is the mass of one cubic centimeter of water. This means that there can be no doubt that the density of water should only be what it is. Can there be any doubt about this? Can. Theorists have calculated that if water did not retain a loose, ice-like structure in the liquid state and its molecules were tightly packed, then the density of water would be much higher. At 25°C it would be equal not to 1.0, but to 1.8 g/cm3.
At what temperature should water boil?
This question is also, of course, strange. After all, water boils at one hundred degrees. Everyone knows this. Moreover, everyone knows that it is the boiling point of water at normal atmospheric pressure that was chosen as one of the reference points of the temperature scale, conventionally designated 100°C.
However, the question is posed differently: at what temperature should water boil? After all, the boiling temperatures of various substances are not random. They depend on the position of the elements that make up their molecules in Mendeleev’s periodic table.
If we compare chemical compounds of different elements with the same composition that belong to the same group of the periodic table, it is easy to notice that the lower the atomic number of an element, the lower its atomic weight, the lower the boiling point of its compounds. Based on its chemical composition, water can be called an oxygen hydride. H2Te, H2Se and H2S are chemical analogues of water. If you monitor their boiling points and compare how the boiling points of hydrides change in other groups of the periodic table, then you can quite accurately determine the boiling point of any hydride, just like any other compound. Mendeleev himself was able to predict the properties of chemical compounds of elements not yet discovered in this way.
If we determine the boiling point of oxygen hydride by its position in the periodic table, it turns out that water should boil at -80 ° C. Consequently, water boils approximately one hundred and eighty degrees higher , than it should boil. The boiling point of water - this is its most common property - turns out to be extraordinary and surprising.
The properties of any chemical compound depend on the nature of the elements that form it and, therefore, on their position in Mendeleev’s periodic table of chemical elements. These graphs show the dependences of the boiling and melting temperatures of hydrogen compounds of groups IV and VI of the periodic table. Water is a striking exception. Due to the very small radius of the proton, the interaction forces between its molecules are so great that it is very difficult to separate them, which is why water boils and melts at abnormally high temperatures.
Graph A. Normal dependence of the boiling point of hydrides of group IV elements on their position in the periodic table.
Graph B. Among the hydrides of group VI elements, water has anomalous properties: water should boil at minus 80 - minus 90 ° C, but it boils at plus 100 ° C.
Graph B. Normal dependence of the melting temperature of hydrides of group IV elements on their position in the periodic table.
Graph D. Among the hydrides of group VI elements, water violates the order: it should melt at minus 100 ° C, and ice icicles melt at 0 ° C.
At what temperature does water freeze?
Isn't it true that the question is no less strange than the previous ones? Well, who doesn’t know that water freezes at zero degrees? This is the second reference point of the thermometer. This is the most common property of water. But even in this case, one can ask: at what temperature should water freeze in accordance with its chemical nature? It turns out that oxygen hydride, based on its position in the periodic table, should have solidified at one hundred degrees below zero.
How many liquid states of water are there?
This question is not so easy to answer. Of course, there is also one thing - the liquid water we are all familiar with. But liquid water has such extraordinary properties that one has to wonder whether such a simple, seemingly non-provoking
no doubt the answer? Water is the only substance in the world that, after melting, first contracts and then begins to expand as the temperature rises. At approximately 4°C, water is at its highest density. This rare anomaly in the properties of water is explained by the fact that in reality liquid water is a complex solution of a completely unusual composition: it is a solution of water in water.
When ice melts, large, complex water molecules are first formed. They retain remnants of the loose crystalline structure of ice and are dissolved in ordinary low-molecular-weight water. Therefore, at first the density of water is low, but as the temperature increases, these large molecules break down and so the density of the water increases until normal thermal expansion takes over, at which point the density of the water falls again. If this is true, then several states of water are possible, but no one knows how to separate them. And it is still unknown whether this will ever be possible. This extraordinary property of water is of great importance for life. In reservoirs, before the onset of winter, the cooling water gradually drops down until the temperature of the entire reservoir reaches 4°C. With further cooling, the colder water remains on top and all mixing stops. As a result, an extraordinary situation is created: a thin layer of cold water becomes like a “warm blanket” for all the inhabitants of the underwater world. At 4°C they clearly feel quite well.
What should be easier - water or ice?
Who doesn’t know this... After all, ice floats on water. Giant icebergs float in the ocean. Lakes in winter are covered with a floating continuous layer of ice. Of course, ice is lighter than water.
But why "of course"? Is it that clear? On the contrary, the volume of all solids increases during melting, and they drown in their own melt. But ice floats in water. This property of water is an anomaly in nature, an exception, and, moreover, an absolutely remarkable exception.
The positive charges in a water molecule are associated with hydrogen atoms. The negative charges are the valence electrons of oxygen. Their relative arrangement in a water molecule can be depicted as a simple tetrahedron.
Let's try to imagine what the world would look like if water had normal properties and ice was, as any normal substance should be, denser than liquid water. In winter, denser ice freezing from above would sink into the water, continuously sinking to the bottom of the reservoir. In summer, the ice, protected by a layer of cold water, could not melt. Gradually, all lakes, ponds, rivers, streams would freeze completely, turning into giant blocks of ice. Finally, the seas would freeze, followed by the oceans. Our beautiful, blooming green world would become a continuous icy desert, covered here and there with a thin layer of melt water.
How many ices are there?
In nature on our Earth there is only one: ordinary ice. Ice is a rock with extraordinary properties. It is solid, but flows like a liquid, and there are huge rivers of ice that flow slowly down from the high mountains. Ice is changeable - it continuously disappears and forms again. Ice is unusually strong and durable - for tens of thousands of years it preserves without changes the bodies of mammoths that accidentally died in glacial cracks. In his laboratories, man managed to discover at least six more different, no less amazing ices. They cannot be found in nature. They can only exist at very high pressures. Ordinary ice is preserved up to a pressure of 208 MPa (megapascals), but at this pressure it melts at - 22 °C. If the pressure is higher than 208 MPa, dense ice appears - ice-III. It is heavier than water and sinks in it. At a lower temperature and higher pressure - up to 300 MPa - even denser ice-P is formed. Pressure above 500 MPa turns ice into ice-V. This ice can be heated to almost 0 ° C, and it will not melt, although it is under enormous pressure. At a pressure of about 2 GPa (gigapascals), ice-VI appears. This is literally hot ice - it can withstand temperatures of 80° C without melting. Ice-VII, found at 3GP pressure, can perhaps be called hot ice. This is the densest and most refractory ice known. It only melts at 190° above zero.
Ice-VII has an unusually high hardness. This ice can even cause sudden disasters. The bearings in which the shafts of powerful power plant turbines rotate develop enormous pressure. If even a little water gets into the grease, it will freeze, even though the bearing temperature is very high. The resulting ice-VII particles, which have enormous hardness, will begin to destroy the shaft and bearing and quickly cause them to fail.
Maybe there is ice in space too?
As if there is, and at the same time very strange. But scientists on Earth discovered it, although such ice cannot exist on our planet. The density of all currently known ice, even at very high pressures, only very slightly exceeds 1 g/cm3. The density of the hexagonal and cubic modifications of ice at very low pressures and temperatures, even close to absolute zero, is slightly less than unity. Their density is 0.94 g/cm3.
But it turned out that in a vacuum, at negligible pressures and at temperatures below -170 ° C, under conditions when the formation of ice occurs when it condenses from steam on a cooled solid surface, absolutely amazing ice appears. Its density is... 2.3 g/cm3. All ice known so far is crystalline, but this new ice is apparently amorphous, characterized by a random relative arrangement of individual water molecules; It does not have a specific crystal structure. For this reason, it is sometimes called glass ice. Scientists are confident that this amazing ice must arise in space conditions and play a big role in the physics of planets and comets. The discovery of such super-dense ice was unexpected for physicists.
What does it take for the ice to melt?
A lot of heat. Much more than it would take to melt the same amount of any other substance. The exceptionally high specific heat of fusion -80 cal (335 J) per gram of ice is also an anomalous property of water. When water freezes, the same amount of heat is released again.
When winter comes, ice forms, snow falls and water gives back heat, warming the ground and air. They resist the cold and soften the transition to harsh winter. Thanks to this wonderful property of water, autumn and spring exist on our planet.
How much heat is needed to heat water?
So many. More than it takes to heat an equal amount of any other substance. It takes one calorie (4.2 J) to heat a gram of water one degree. This is more than double the heat capacity of any chemical compound.
Water is a substance that is extraordinary in its most ordinary properties for us. Of course, this ability of water is very important not only when cooking dinner in the kitchen. Water is the great distributor of heat throughout the Earth. Heated by the Sun under the equator, it transfers heat in the World Ocean with giant streams of sea currents to the distant polar regions, where life is possible only thanks to this amazing feature of water.
Why is the water in the sea salty?
This is perhaps one of the most important consequences of one of the most amazing properties of water. In its molecule, the centers of positive and negative charges are strongly displaced relative to each other. Therefore, water has an exceptionally high, anomalous value of dielectric constant. For water, e = 80, and for air and vacuum, e = 1. This means that any two opposite charges in water are mutually attracted to each other with a force 80 times less than in air. After all, according to Coulomb's law:
But still, intermolecular bonds in all bodies, which determine the strength of the body, are caused by the interaction between the positive charges of atomic nuclei and negative electrons. On the surface of a body immersed in water, the forces acting between molecules or atoms are weakened under the influence of water by almost a hundred times. If the remaining bond strength between molecules becomes insufficient to withstand the effects of thermal motion, molecules or atoms of the body begin to break away from its surface and pass into water. The body begins to dissolve, breaking up either into individual molecules, like sugar in a glass of tea, or into charged particles - ions, like table salt.
It is thanks to its abnormally high dielectric constant that water is one of the most powerful solvents. It is even capable of dissolving any rock on the earth's surface. Slowly and inevitably, it destroys even granites, leaching easily soluble components from them.
Streams, rivers and rivers carry impurities dissolved in water into the ocean. The water from the ocean evaporates and returns to the earth again to continue its eternal work again and again. And dissolved salts remain in the seas and oceans.
Do not think that water dissolves and carries into the sea only what is easily soluble, and that sea water contains only ordinary salt that stands on the dinner table. No, sea water contains almost all the elements that exist in nature. It contains magnesium, calcium, sulfur, bromine, iodine, and fluorine. Iron, copper, nickel, tin, uranium, cobalt, even silver and gold were found in it in smaller quantities. Chemists found over sixty elements in sea water. Probably all the others will be found as well. Most of the salt in sea water is table salt. That's why the water in the sea is salty.
Is it possible to run on the surface of water?
Can. To see this, look at the surface of any pond or lake in summer. A lot of living and fast people not only walk on water, but also run. If we consider that the support area of the legs of these insects is very small, then it is not difficult to understand that, despite their low weight, the surface of the water can withstand significant pressure without breaking through.
Can water flow upward?
Yes maybe. This happens all the time and everywhere. The water itself rises up in the soil, wetting the entire thickness of the earth from the groundwater level. The water itself rises up through the capillary vessels of the tree and helps the plant deliver dissolved nutrients to great heights - from the roots deeply hidden in the ground to the leaves and fruits. The water itself moves upward in the pores of the blotting paper when you have to dry a blot, or in the fabric of a towel when you wipe your face. In very thin tubes - in capillaries - water can rise to a height of several meters.
What explains this?
Another remarkable feature of water is its exceptionally high surface tension. Water molecules on its surface experience the forces of intermolecular attraction only on one side, and in water this interaction is anomalously strong. Therefore, every molecule on its surface is drawn into the liquid. As a result, a force arises that tightens the surface of the liquid. In water it is especially strong: its surface tension is 72 mN/m (millinewtons per meter).
Can water remember?
This question sounds, admittedly, very unusual, but it is quite serious and very important. It concerns a large physico-chemical problem, which in its most important part has not yet been investigated. This question has just been posed in science, but it has not yet found an answer to it.
The question is: does the previous history of water influence its physical and chemical properties and is it possible, by studying the properties of water, to find out what happened to it earlier - to make the water itself “remember” and tell us about it. Yes, perhaps, as surprising as it may seem. The easiest way to understand this is with a simple, but very interesting and extraordinary example - the memory of ice.
Ice is water after all. When water evaporates, the isotopic composition of water and steam changes. Light water evaporates, although to an insignificant extent, faster than heavy water.
When natural water evaporates, the composition changes in the isotopic content of not only deuterium, but also heavy oxygen. These changes in the isotopic composition of steam have been very well studied, and their dependence on temperature has also been well studied.
Recently, scientists performed a remarkable experiment. In the Arctic, in the thickness of a huge glacier in northern Greenland, a borehole was sunk and a giant ice core almost one and a half kilometers long was drilled and extracted. The annual layers of growing ice were clearly visible on it. Along the entire length of the core, these layers were subjected to isotopic analysis, and based on the relative content of heavy isotopes of hydrogen and oxygen - deuterium and 18O - the formation temperatures of annual ice layers in each core section were determined. The date of formation of the annual layer was determined by direct counting. In this way, the climate situation on Earth was restored for a millennium. Water managed to remember and record all this in the deep layers of the Greenland glacier.
As a result of isotopic analyzes of ice layers, scientists constructed a climate change curve on Earth. It turned out that our average temperature is subject to secular fluctuations. It was very cold in the 15th century, at the end of the 17th century. and at the beginning of the 19th century. The hottest years were 1550 and 1930.
Then what is the mystery of the “memory” of water?
The fact is that in recent years, science has gradually accumulated many amazing and completely incomprehensible facts. Some of them are firmly established, others require quantitative reliable confirmation, and all of them are still waiting to be explained.
For example, no one yet knows what happens to water flowing through a strong magnetic field. Theoretical physicists are absolutely sure that nothing can and will not happen to it, reinforcing their conviction with completely reliable theoretical calculations, from which it follows that after the cessation of the magnetic field, the water should instantly return to its previous state and remain as it was . And experience shows that it changes and becomes different.
Is there a big difference? Judge for yourself. From ordinary water in a steam boiler, dissolved salts, released, are deposited in a dense and rock-hard layer on the walls of the boiler pipes, and from magnetized water (as it is now called in technology) they fall out in the form of a loose sediment suspended in the water. It seems like the difference is small. But it depends on the point of view. According to workers at thermal power plants, this difference is extremely significant, since magnetized water ensures normal and uninterrupted operation of giant power plants: the walls of steam boiler pipes do not become overgrown, heat transfer is higher, and electricity generation is higher. Magnetic water treatment has long been installed at many thermal stations, but neither engineers nor scientists know how and why it works. In addition, it has been observed experimentally that after magnetic treatment of water, the processes of crystallization, dissolution, adsorption are accelerated in it, and wetting changes... however, in all cases the effects are small and difficult to reproduce.
The effect of a magnetic field on water (necessarily fast-flowing) lasts for small fractions of a second, but the water “remembers” this for tens of hours. Why is unknown. In this matter, practice is far ahead of science. After all, it is further unknown what exactly magnetic treatment affects - water or the impurities contained in it. There is no such thing as pure water.
The “memory” of water is not limited to the preservation of the effects of magnetic influence. In science, many facts and observations exist and are gradually accumulating, showing that water seems to “remember” that it was previously frozen.
Melt water, recently formed by melting a piece of ice, also seems to be different from the water from which this piece of ice was formed. In melt water, seeds germinate faster and better, sprouts develop faster; further, chickens that receive melt water seem to grow and develop faster. In addition to the amazing properties of melt water, established by biologists, purely physical and chemical differences are also known, for example, melt water differs in viscosity and dielectric constant. The viscosity of melt water takes on its usual value for water only 3-6 days after melting. Why this is so (if it is so), no one else knows.
Most researchers call this area of phenomena the “structural memory” of water, believing that all these strange manifestations of the influence of the previous history of water on its properties are explained by changes in the fine structure of its molecular state. Maybe this is so, but... to name it does not mean to explain it. There is still an important problem in science: why and how water “remembers” what happened to it.
Where did water come from on Earth?
Streams of cosmic rays - streams of particles with enormous energy - are forever permeating the Universe in all directions. Most of them contain protons - the nuclei of hydrogen atoms. In its movement in space, our planet is constantly subjected to “proton bombardment.” Penetrating the upper layers of the earth's atmosphere, protons capture electrons, turn into hydrogen atoms and immediately react with oxygen to form water. Calculations show that every year almost one and a half tons of such “cosmic” water is born in the stratosphere. At high altitudes at low temperatures, the elasticity of water vapor is very small and water molecules, gradually accumulating, condense on cosmic dust particles, forming mysterious noctilucent clouds. Scientists suggest that they consist of tiny ice crystals that arose from such “cosmic” water. Calculations showed that the water that appeared on Earth in this way throughout its history would be just enough to give birth to all the oceans of our planet. So, water came to Earth from space? But...
Geochemists do not consider water a heavenly guest. They are convinced that she is of earthly origin. The rocks that make up the earth's mantle, which lies between the central core of the Earth and the earth's crust, melted in places under the influence of the accumulating heat of radioactive decay of isotopes. Of these, volatile components were released: nitrogen, chlorine, carbon and sulfur compounds, and most of all water vapor was released.
How much could all volcanoes emit during eruptions during the entire existence of our planet?
Scientists have calculated this too. It turned out that such erupted “geological” water would also be just enough to fill all the oceans.
In the central parts of our planet, forming its core, there is probably no water. It is unlikely that it could exist there. Some scientists believe that further, even if oxygen and hydrogen are present there, then they must, together with other elements, form new to science, unknown metal-like forms of compounds that have a high density and are stable at the enormous pressures and temperatures that reign in the center of the globe .
Other researchers are confident that the core of the globe consists of iron. What actually is not so far from us, under our feet, at depths exceeding 3 thousand km, no one yet knows, but there is probably no water there.
Most of the water in the Earth's interior is found in its mantle - layers located under the earth's crust and extending to a depth of approximately 3 thousand km. Geologists believe that at least 13 billion cubic meters are concentrated in the mantle. km of water.
The topmost layer of the earth's shell - the earth's crust - contains approximately 1.5 billion cubic meters. km of water. Almost all the water in these layers is in a bound state - it is part of rocks and minerals, forming hydrates. You cannot bathe in this water and you cannot drink it.
The hydrosphere, the water shell of the globe, is formed by approximately another 1.5 billion cubic meters. km of water. Almost all of this amount is contained in the World Ocean. It occupies about 70% of the entire earth's surface, its area is over 360 million square meters. km. From space, our planet does not look like a globe at all, but rather like a water balloon.
The average depth of the Ocean is about 4 km. If we compare this “bottomless depth” with the size of the globe itself, the average diameter of which is equal to km, then, on the contrary, we will have to admit that we live on a wet planet, it is only slightly moistened with water, and even then not over the entire surface. The water in the oceans and seas is salty - you cannot drink it.
There is very little water on land: only about 90 million cubic meters. km. Of these, more than 60 million cubic meters. km is underground, almost all of it is salt water. About 25 million cubic meters. km of solid water lies in mountainous and glacial regions, in the Arctic, Greenland, and Antarctica. These water reserves on the globe are protected.
All lakes, swamps, man-made reservoirs and soil contain another 500 thousand cubic meters. km of water.
Water is also present in the atmosphere. There is always a lot of water vapor in the air, even in the most arid deserts, where there is not a drop of water and it never rains. In addition, clouds are always floating across the sky, clouds are gathering, it is snowing, it is raining, and fog is spreading over the ground. All these reserves of water in the atmosphere have been accurately calculated: all of them taken together amount to only 14 thousand cubic meters. km.
The concept of a molecule (and its derivative ideas about the molecular structure of matter, the structure of the molecule itself) allows us to understand the properties of substances that create the world. Modern, like early, physical and chemical research relies and is based on a grandiose discovery about the atomic and molecular structure of matter. A molecule is a single “detail” of all substances, the existence of which was suggested by Democritus. Therefore, it is its structure and relationship with other molecules (forming a certain structure and composition) that determines/explains all the differences between substances, their type and properties.
The molecule itself, being not the smallest component of a substance (which is an atom), has a certain structure and properties. The structure of a molecule is determined by the number of certain atoms included in it and the nature of the bond (covalent) between them. This composition remains unchanged, even if the substance is transformed into another state (as, for example, happens with water - this will be discussed later).
The molecular structure of a substance is fixed by a formula that provides information about atoms and their number. In addition, the molecules that make up a substance/body are not static: they themselves are mobile - the atoms rotate, interacting with each other (attract/repel).
Characteristics of water, its condition
The composition of a substance such as water (as well as its chemical formula) is familiar to everyone. Each of its molecules is made up of three atoms: an oxygen atom, denoted by the letter “O”, and hydrogen atoms – the Latin “H”, in the amount of 2. The shape of the water molecule is not symmetrical (similar to an isosceles triangle).
Water, as a substance, its constituent molecules, reacts to the external “situation”, environmental indicators - temperature, pressure. Depending on the latter, water can change its state, of which there are three:
- The most common, natural state for water is liquid. A molecular structure (dihydrol) of a peculiar order in which single molecules fill (by hydrogen bonds) the voids.
- A state of vapor in which the molecular structure (hydrol) is represented by single molecules between which hydrogen bonds are not formed.
- The solid state (ice itself) has a molecular structure (trihydrol) with strong and stable hydrogen bonds.
In addition to these differences, naturally, the methods of “transition” of a substance from one state (liquid) to others also differ. These transitions both transform the substance and provoke the transfer of energy (release/absorption). Among them there are direct processes - the transformation of liquid water into steam (evaporation), into ice (freezing) and reverse processes - into liquid from steam (condensation), from ice (melting). Also, the states of water - vapor and ice - can be transformed into each other: sublimation - ice into steam, sublimation - the reverse process.
Specificity of ice as a state of water
It is widely known that ice freezes (transforms from water) when the temperature crosses the downward boundary of zero degrees. Although, this understandable phenomenon has its own nuances. For example, the state of ice is ambiguous; its types and modifications are different. They differ primarily in the conditions under which they arise - temperature, pressure. There are as many as fifteen such modifications.
Ice in its different types has a different molecular structure (the molecules are indistinguishable from water molecules). Natural and natural ice, in scientific terminology denoted as ice Ih, is a substance with a crystalline structure. That is, each molecule with four surrounding “neighbors” (the distance between all is equal) creates a geometric figure, a tetrahedron. Other phases of ice have a more complex structure, for example the highly ordered structure of trigonal, cubic or monoclinic ice.
The main differences between ice and water at the molecular level
The first and not directly related to the molecular structure of water and ice difference between them is the density indicator of the substance. The crystalline structure inherent in ice, when formed, contributes to a simultaneous decrease in density (from almost 1000 kg/m³ to 916.7 kg/m³). And this stimulates an increase in volume by 10%. 
The main difference in the molecular structure of these aggregate states of water (liquid and solid) is number, type and strength of hydrogen bonds between molecules. In ice (solid state), they unite five molecules, and the hydrogen bonds themselves are stronger.
The molecules of water and ice substances themselves, as mentioned earlier, are the same. But in ice molecules, the oxygen atom (to create a crystalline “lattice” of the substance) forms hydrogen bonds (two) with “neighboring” molecules.
What distinguishes the substance of water in its different states (aggregate) is not only the structure of the arrangement of molecules (molecular structure), but also their movement, the force of interconnection/attraction between them. Water molecules in the liquid state are attracted rather weakly, ensuring the fluidity of water. In solid ice, the attraction of molecules is strongest, and therefore their motor activity is low (it ensures the constancy of the shape of the ice).
Of the 14 currently known forms of solid water in nature, we find only one - ice. The rest are formed under extreme conditions and are inaccessible for observations outside special laboratories. The most intriguing property of ice is its amazing variety of external manifestations. With the same crystalline structure, it can look completely different, taking the form of transparent hailstones and icicles, flakes of fluffy snow, a dense shiny crust of firn on a snow field, or giant glacial masses.
In the small Japanese city of Kaga, located on the western coast of the island of Honshu, there is an unusual museum. Snow and ice. It was founded by Ukihiro Nakaya, the first person who learned to grow artificial snowflakes in the laboratory, as beautiful as those falling from the sky. In this museum, visitors are surrounded on all sides by regular hexagons, because it is precisely this “hexagonal” symmetry that is characteristic of ordinary ice crystals (by the way, the Greek word kristallos actually means “ice”). It determines many of its unique properties and makes snowflakes, with all their infinite variety, grow in the shape of stars with six, less often three or twelve rays, but never with four or five.
Molecules in openwork
The key to the structure of solid water lies in the structure of its molecule. H2O can be simplistically represented as a tetrahedron (a pyramid with a triangular base). In the center there is oxygen, in two vertices there is a hydrogen, more precisely a proton, the electrons of which are involved in the formation of a covalent bond with oxygen. The two remaining vertices are occupied by pairs of oxygen valence electrons, which do not participate in the formation of intramolecular bonds, which is why they are called lone.
When a proton of one molecule interacts with a pair of lone oxygen electrons of another molecule, a hydrogen bond is formed, less strong than an intramolecular bond, but powerful enough to hold neighboring molecules together. Each molecule can simultaneously form four hydrogen bonds with other molecules at strictly defined angles, which do not allow the creation of a dense structure when frozen. This invisible framework of hydrogen bonds arranges the molecules in a lacy network with hollow channels. As soon as the ice is heated, the lace collapses: water molecules begin to fall into the voids of the mesh, leading to a more dense structure of the liquid, which is why water is heavier than ice.Ice, which forms at atmospheric pressure and melts at 0°C, is the most common, but still not fully understood, substance. Much in its structure and properties looks unusual. At the sites of the crystal lattice of ice, oxygen atoms are arranged in an orderly manner, forming regular hexagons, but hydrogen atoms occupy a variety of positions along the bonds. This behavior of atoms is generally atypical - as a rule, in a solid substance everyone obeys the same law: either all atoms are arranged in an orderly manner, and then it is a crystal, or randomly, and then it is an amorphous substance.
Ice is difficult to melt, no matter how strange it may sound. If there were no hydrogen bonds holding water molecules together, it would melt at 90°C. At the same time, when water freezes, it does not decrease in volume, as happens with most known substances, but increases due to the formation of an openwork structure of ice.The “oddities” of ice also include the generation of electromagnetic radiation by its growing crystals. It has long been known that most of the impurities dissolved in water are not transferred to the ice when it begins to grow; in other words, it freezes out. Therefore, even on the dirtiest puddle, the ice film is clean and transparent. Impurities accumulate at the interface between solid and liquid media, in the form of two layers of electrical 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 emits 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 emits differently than one covered with lateral processes, and the radiation of growing grains differs from what occurs when crystals crack. By the shape, sequence, frequency and amplitude of the radiation pulses, one can determine at what speed the ice freezes and what kind of ice structure is obtained.
Wrong ice
In the solid state, water has, according to the latest data, 14 structural modifications. Some of them are crystalline (the majority of them), some are amorphous, but they all differ from each other in the relative arrangement of water molecules and properties. True, everything except the ice we are familiar with 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. For example, at temperatures below 110°C, water vapor precipitates on a metal plate in the form of octahedra and cubes several nanometers in size - this is the so-called cubic ice. If the temperature is slightly above 110°, and the vapor concentration is very low, a layer of extremely dense amorphous ice forms on the plate.
The last two modifications of ice XIII and XIV were discovered by scientists from Oxford quite recently, in 2006. The 40-year-old prediction 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 molecules of ultra-pure supercooled water come together in such quantities to form a crystal nucleus, difficult. The catalyst helped: hydrochloric acid, which increased the mobility of water molecules at low temperatures. Such modifications of ice cannot form in terrestrial nature, but they can be looked for on the frozen satellites of other planets.
The commission decided soA snowflake is a single crystal of ice, a variation on the theme of a hexagonal crystal, but one that grew quickly under non-equilibrium conditions. The most inquisitive minds have been struggling with the secret of their beauty and endless diversity for centuries. Astronomer Johannes Kepler wrote a whole treatise “On Hexagonal Snowflakes” in 1611. In 1665, Robert Hooke, in a huge volume of sketches of everything he saw with a microscope, published many drawings of snowflakes of various shapes. The first successful photograph of a snowflake under a microscope was taken in 1885 by American farmer Wilson Bentley. From then on he couldn't stop. Until the end of his life, for more than forty years, Bentley photographed them. More than five thousand crystals, and not a single one is the same.
The most famous followers of Bentley's cause are the already mentioned Ukihiro Nakaya and the American physicist Kenneth Libbrecht. Nakaya was the first to suggest that the size and shape of snowflakes depend on air temperature and moisture content, and brilliantly confirmed this hypothesis experimentally by growing ice crystals of different shapes in the laboratory. And Libbrecht even began to grow custom-made snowflakes of a predetermined shape.
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 pieces of ice less than a tenth of a millimeter in size 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 completely identical ice needles and lateral processes begin to grow. They are the same simply because the temperature and humidity around the embryo are also the same. On them, in turn, lateral shoots and branches grow, like on a tree. Such crystals are called dendrites, that is, similar to wood.
Moving up and down in a cloud, a snowflake encounters conditions with different temperatures and concentrations of water vapor. Its shape changes, obeying the laws of hexagonal symmetry to the last. This is how snowflakes become different. Although theoretically, in the same cloud at the same altitude, they can “emerge” identical. But each has its own path to the ground, which is quite long; on average, a snowflake falls at a speed of 0.9 km per hour. This means that each has its own history and its own final form. The ice that forms a snowflake is transparent, but when there are a lot of them, sunlight, reflected and scattered on numerous faces, gives us the impression of a white opaque mass - we call it snow.
To avoid confusion with the variety of snowflakes, the International Commission on Snow and Ice adopted in 1951 a fairly simple classification of ice crystals: plates, star crystals, columns or columns, needles, spatial dendrites, tipped columns and irregular shapes. And three more types of icy precipitation: fine snow pellets, ice pellets and hail.The growth of frost, hoarfrost and patterns on glass is subject to the same laws. These phenomena, like snowflakes, are formed by condensation, molecule by molecule, on the ground, grass, trees. Patterns on the window appear in frosty weather, when moisture from warm room air condenses on the surface of the glass. But hailstones are formed when drops of water freeze or when ice in clouds saturated with water vapor freezes in dense layers onto the embryos of snowflakes. Other, already formed snowflakes can freeze onto hailstones, fusing with them, due to which the hailstones take on the most bizarre shapes.
For us on Earth, one solid modification of water—ordinary ice—is enough. It literally permeates all areas of human habitation or stay. Collecting in huge quantities, snow and ice form special structures with properties that are fundamentally different from those of individual crystals or snowflakes. Mountain glaciers, ice covers of water areas, permafrost, and simply seasonal snow cover significantly influence 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 fluctuations in the level of the World Ocean. And ice is so important for the appearance of our planet and the comfortable habitat of living creatures on it that scientists have allocated a special environment for it - the cryosphere, which extends its domain high into the atmosphere and deep into the earth's crust.
Olga Maksimenko, Candidate of Chemical Sciences
