The three-dimensional state of liquid water is difficult to investigate, but much has been studied by analyzing the structure of ice crystals. Four neighboring oxygen atoms with hydrogen interaction occupy the vertices of the 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 in place by liquid water, the structure of which is irregular. Most of the hydrogen bonds are distorted. For the destruction of the crystal lattice of ice with hydrogen bonding requires a large mass of energy in the form of heat.
Features of the appearance of ice (Ih)
Many of the inhabitants ask what kind of crystal lattice the ice has. It should be noted that the density of most substances increases during freezing, when molecular movements slow down and tightly packed crystals form. The density of water also increases when 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-bound ice crystal with its lattice and lower density, in which each water molecule is rigidly bound by the above element and four other values, and at the same time moves fast enough to have a larger mass. Since such an action occurs, the liquid freezes from top to bottom. This has important biological results, due to which the layer of ice on the pond isolates living things away from extreme cold. In addition, two additional properties of water are associated with its hydrogen characteristics: specific heat and evaporation.
Detailed description of structures
The first criterion is the amount needed to increase the temperature of 1 gram of substance by 1 ° C. To increase the degrees of water, a relatively large part of the heat is required, because each molecule is involved in numerous hydrogen bonds, which must be destroyed 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 crucial because the rate of most biochemical reactions is sensitive.
The heat of vaporization of water is also significantly higher than that of many other liquids. Converting this body into gas requires a large amount of heat, because hydrogen bonds must be broken so that water molecules can be deployed from each other and enter the indicated phase. Variable bodies are constant dipoles and can interact with other similar compounds and those that ionize and dissolve.
Other substances mentioned above may come into contact only in the presence of polarity. It is this connection that is involved in the structure of these elements. In addition, it can be aligned around these particles formed from electrolytes, so that the negative oxygen atoms of the water molecules are oriented to cations, and the positive ions and hydrogen atoms are oriented to anions.
In solids , as a rule, molecular crystal lattices and atomic ones are formed. That is, if iodine is constructed in such a way that I 2 is present in it , then CO 2 molecules are present in solid carbon dioxide, that is, in dry ice, in the nodes of the crystal lattice. When interacting with similar substances, the ionic crystal lattice has ice. Graphite, for example, having an atomic structure based on carbon, is not able to change it, just like diamond.
What happens when a table salt crystal dissolves in water: polar molecules are attracted to charged elements in the crystal, which leads to the formation of similar particles of sodium and chloride on its surface, as a result, these bodies are deployed from each other, and it begins to dissolve. From here it can be observed that ice has a crystal lattice with an ionic bond. 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 sphere of salvation and usually contains several layers of solvent particles.
Dry ice crystal lattice
Variables or an ion surrounded by elements are said to be sulfated. When water acts as a solvent, such particles are hydrated. Thus, any polar molecule has a tendency to solvation by elements of the liquid body. In dry ice, the type of crystal lattice in the state of aggregation forms atomic bonds that are unchanged. Another thing is crystalline ice (frozen water). Ionic organic compounds, such as carboxylases and protonated amines, must have solubility in the hydroxyl and carbonyl groups. Particles contained in such structures move between the molecules, and their polar systems form hydrogen bonds with this body.
Of course, the amount of the last groups indicated in a 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 mixed with water, but larger hydrocarbons with single hydroxyl compounds are much less diluted in liquids.
Hexagonal Ih is similar in shape to an atomic crystal lattice. In ice and all natural snow on Earth, it looks exactly like that. This is evidenced by the symmetry of the crystal lattice of ice grown from water vapor (i.e. snowflakes). It has been in the space group P 63 / mm since 194; D 6h, Laue class 6 / mm; similar to β- having a multiple of 6 screw axis (rotation around in addition to the shift along it). It has a fairly open structure with a low density, 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 gratings and their constituent elements
Crystals can be considered as crystalline models consisting of sheets located one above the 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 liquid in a constant tunneling flow. This is enhanced by the scattering of neutrons, showing the density of their scattering halfway between oxygen atoms, which indicates localization and consistent motion. There is a similarity of ice with the atomic, molecular crystal lattice.
Molecules have a stepwise 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 ideal hexagonal symmetry, as the unit cell is 0.3% shorter in the direction of this chain. All molecules experience the same molecular environment. Inside each box there is enough space to hold particles of interstitial water. Although this is generally not considered, they have recently been effectively detected by neutron diffraction by a powdery ice crystal lattice.
Substance Change
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 in MPa. Equations of state are available, in addition to them some simple inequalities connecting the change in physical properties with the temperature of hexagonal ice and its aqueous suspensions. Hardness varies depending on degrees increasing from or below gypsum (≤2) at 0 ° C to feldspar (6 on the Mohs scale) 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 other equivalent side faces are called parts of the prism {1 0 -1 0} s 5.94 μJ cm -2 . Secondary surfaces {1 1 -2 0} with 6.90 μJ ˣ cm -2 can be formed along planes formed by the sides of the structures.
A similar structure shows an abnormal decrease in thermal conductivity with increasing pressure (like cubic and low-density amorphous ice), 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 that describe 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-frequency oscillation generation showed 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 accepted 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 hexagonal ice structures are available.
Development features
The minimum number of water molecules required for ice nucleation is approximately 275 ± 25, as well as for a complete icosahedral cluster 280. The formation occurs with a coefficient of 10 10 at the air-water interface, and not in bulk water. The growth of ice crystals depends on different growth rates of different energies. Water should be protected from freezing during cryopreservation of biological samples, food and organs.
This is usually achieved by fast cooling rates, using small samples and a cryo-conservative, as well as increasing pressure to form ice nuclei and prevent cell damage. The free energy of ice / liquid increases from ~ 30 mJ / m 2 at atmospheric pressure to 40 mJ / m -2 at 200 MPa, which indicates the reason why this effect occurs.
What type of crystal lattice is characteristic of ice
Alternatively, they can grow faster from the surfaces of the prism (S2), on a randomly disturbed surface of rapidly frozen or excited lakes. The growth from the faces {1 1 -2 0} is at least the same, but turns them into the bases of a prism. Data on the development of an 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 rate of diffusion at a low degree of subcooling, i.e. <2 ° C, which leads to a greater number of them.
But it is limited by the kinetics of development at higher levels of lowering degrees> 4 ° C, which leads to needle growth. This form is similar to the structure of dry ice (it has a crystal lattice with a hexagonal structure), various characteristics of the surface development and the temperature of the surrounding (supercooled) water, which is located behind the flat forms of snowflakes.
The formation of ice in the atmosphere deeply affects the formation and properties of clouds. Feldspars found in desert dust, which enters the atmosphere in millions of tons per year, are important educators. Computer simulation showed that this is due to the nucleation of the planes of prismatic ice crystals on the planes of the high-energy surface.
Some other elements and grids
Dissolved substances (with the exception of very small helium and hydrogen, which can enter the internodes) cannot be included in the Ih structure at atmospheric pressure, but are displaced to the surface or amorphous layer between particles of a microcrystalline body. At the nodes of the crystal lattice of dry ice, there are some other elements: chaotropic ions, such as NH 4 + and Cl - , which are included in easier liquid freezing than other cosmotropic ions, such as Na + and SO 4 2- , therefore, they cannot be removed, due to the fact that they form a thin film of the remaining liquid between the crystals. This can lead to electric surface charging due to dissociation of surface water 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 alkaline.
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. The rapidly growing {1 0 -1 0} prism surface, where pairs of newly attached particles can be bonded to each other by hydrogen (one of its bonds / two element molecules). The fastest growing face is {1 1 -2 0} (secondary prismatic), where chains of newly attached particles can interact with each other by a hydrogen bond. One of its chains / element molecules is a form that forms ridges that divide and encourage the transformation into two sides of the prism.
Entropy of the zero point
It can be defined as S 0 = k B ˣ Ln ( N E0 ), where k B is the Boltzmann constant, N E is the number of configurations at 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 apply to a very large number of energetically close states, obey the "rules of ice". Zero point entropy is a mess 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 the spread of energy levels) than to determine it experimentally.
Scientists and their works in this field
It can be defined as S 0 = k B ˣ Ln ( N E0 ), where k B is the Boltzmann constant, N E is the number of configurations at 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 apply to a very large number of energetically close states, obey the "rules of ice". Zero point entropy is a mess 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 the spread of energy levels) 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). Found a disorder of the zero point ZPE, J ˣ mol -1 ˣ K -1 and others. , .