Physics. Molecules. Arrangement of molecules in gaseous, liquid and solid distance.
- In the gaseous state, the molecules are not connected to each other, they are located at a great distance from each other. Brownian motion. The gas can be compressed relatively easily.
In a liquid, the molecules are close together, vibrating together. Almost incompressible.
In a solid - the molecules are arranged in a strict order (in crystal lattices), there is no movement of the molecules. Compression will not succumb. - The structure of matter and the beginning of chemistry:
http://samlib.ru/a/anemow_e_m/aa0.shtml
(without registration and SMS messages, in a convenient text format: you can use Ctrl+C) - It is by no means possible to agree that in the solid state the molecules do not move.
Movement of molecules in gases
In gases, the distance between molecules and atoms is usually much larger than the size of the molecules, and the attractive forces are very small. Therefore, gases do not have their own shape and constant volume. Gases are easily compressed because the repulsive forces at large distances are also small. Gases have the property of expanding indefinitely, filling the entire volume provided to them. Gas molecules move at very high speeds, collide with each other, bounce off each other in different directions. Numerous impacts of molecules on the walls of the vessel create gas pressure.
Movement of molecules in liquids
In liquids, molecules not only oscillate around the equilibrium position, but also jump from one equilibrium position to the next. These jumps happen periodically. The time interval between such jumps is called the average time of settled life (or average relaxation time) and is denoted by the letter?. In other words, the relaxation time is the time of oscillation around one specific equilibrium position. At room temperature, this time is on average 10–11 s. The time of one oscillation is 10-1210-13 s.
The time of settled life decreases with increasing temperature. The distance between liquid molecules is smaller than the size of the molecules, the particles are close to each other, and the intermolecular attraction is large. However, the arrangement of liquid molecules is not strictly ordered throughout the volume.
Liquids, like solids, retain their volume, but do not have their own shape. Therefore, they take the form of the vessel in which they are located. A liquid has the property of fluidity. Due to this property, the liquid does not resist shape change, it compresses little, and its physical properties are the same in all directions inside the liquid (liquid isotropy). The nature of molecular motion in liquids was first established by the Soviet physicist Yakov Ilyich Frenkel (1894-1952).
Movement of molecules in solids
Molecules and atoms of a solid body are arranged in a certain order and form a crystal lattice. Such solids are called crystalline. The atoms oscillate about the equilibrium position, and the attraction between them is very strong. Therefore, solid bodies under normal conditions retain their volume and have their own shape.
- In gaseous-move randomly, cut in
In liquid-moving in line with each other
In solid - do not move.
Topic: Three states of matter
I option
I.How are molecules arranged in solids and how do they move?
Molecules are located at distances smaller than the dimensions of the molecules themselves and move freely relative to each other. Molecules are located at large distances from each other (compared to the size of the molecules) and move randomly. Molecules are arranged in a strict order and vibrate around certain equilibrium positions.
II.Which of the following properties belong to gases?
Have a certain volume Occupy the volume of the entire vessel Take the shape of the vessel Slightly compressed Easy to compress
III.Will the volume of gas change if it is pumped from a vessel with a capacity of1 literin a 2 liter container?
IV. Molecules are located at large distances from each other (in relation to the size of the molecules), weakly interact with each other, and move randomly. What is this body?
Gas Solid Liquid No such body
v.What is the state of the steel?
Only in the solid state Only in the liquid state Only in the gaseous state In all three states
Topic: Three states of matter
II option
I.How are the molecules of liquids arranged and how do they move?
The molecules are located at distances commensurate with the size of the molecules themselves, and move freely relative to each other. Molecules are located at large distances (compared to the size of the molecules) from each other and move randomly. Molecules are arranged in a strict order and vibrate around certain equilibrium positions.
II.Which of the following properties belong to gases?
Occupies the entire volume provided to them Difficult to compress Have a crystalline structure Easy to compress Do not have their own shape
III.A beaker contains 100 cm3 of water. It is poured into a glass with a capacity of 200 cm3. Will the volume of water change?
IV. Molecules are densely packed, strongly attracted to each other, each molecule oscillates around a certain position. What is this body?
Gas Liquid Solid body There are no such bodies
v.What state can water be in?
Only in liquid state Only in gaseous state Only in solid state In all three states
Topic: Three states of matter
III option
I.How are gas molecules arranged and how do they move?
Molecules are located at distances smaller than the size of the molecules themselves, and move freely relative to each other. Molecules are located at distances many times the size of the molecules themselves, and move randomly. Molecules are arranged in a strict order and vibrate around certain positions.
II.Which of the following properties belong to solids?
Difficult to change shape Occupies the entire volume provided to them Retain a constant shape Easily change shape Difficult to compress
III.Will the volume of gas change if it is pumped from a cylinder with a capacity of 20 liters to a cylinder with a capacity of .40 liters?
Increase by 2 times Decrease by 2 times No change
IV. Is there such a substance in which the molecules are located at large distances, are strongly attracted to each other and oscillate around certain positions?
Gas Liquid Solid No such substance exists
v.What is the state of mercury?
Only in liquid Only in solid Only in gaseous All three states
Topic: Three states of matter
IV option
I. Below is the behavior of molecules in solid, liquid and gaseous bodies. What is common for liquids and gases?
The fact that molecules are located at distances smaller than the size of the molecules themselves and move freely relative to each other That the molecules are located at large distances from each other and move randomly That the molecules move randomly relative to each other That the molecules are arranged in a strict order and oscillate near certain positions
II.Which of the following properties belong to solids?
Have a certain volume Occupy the volume of the entire vessel Take the shape of the vessel Slightly compressed Easy to compress
III.The bottle contains 0.5 liters of water. It is poured into a flask with a capacity of 1 liter. Will the volume of water change?
Increase Decrease No change
IV. The molecules are arranged so that the distance between them is less than the size of the molecules themselves. They are strongly attracted to each other and move from place to place. What is this body?
Gas Liquid Solid
v.What state can alcohol be in?
Only in the solid state Only in the liquid state Only in the gaseous state In all three states
Answers to tests
I option II - 2, 5 | II option II - 1, 4, 5 | III option II - 1, 3, 5 | IV option II - 1, 4 |
Molecules and atoms of a solid body are arranged in a certain order and form crystal lattice. Such solids are called crystalline. The atoms oscillate about the equilibrium position, and the attraction between them is very strong. Therefore, solid bodies under normal conditions retain volume and have their own shape.
Thermal equilibrium is the state of thermodynamic systems into which it spontaneously passes after a sufficiently long period of time in conditions of isolation from the environment.
Temperature is a physical quantity that characterizes the average kinetic energy of the particles of a macroscopic system in a state of thermodynamic equilibrium. In an equilibrium state, the temperature has the same value for all macroscopic parts of the system.
Degree Celsius(symbol: °C) is a common unit of temperature used in the International System of Units (SI) along with the kelvin.
Mercury medical thermometer
Mechanical thermometer
The degree Celsius is named after the Swedish scientist Anders Celsius, who in 1742 proposed a new scale for measuring temperature. Zero on the Celsius scale was the melting point of ice, and 100° was the boiling point of water at standard atmospheric pressure. (Initially, Celsius took the melting temperature of ice as 100 °, and the boiling point of water as 0 °. And only later did his contemporary Carl Linnaeus “turn over” this scale). This scale is linear in the range 0-100° and also continues linearly in the region below 0° and above 100°. Linearity is a major issue with accurate temperature measurements. Suffice it to mention that a classic thermometer filled with water cannot be marked for temperatures below 4 degrees Celsius, because in this range the water begins to expand again.
The original definition of the degree Celsius depended on the definition of standard atmospheric pressure, because both the boiling point of water and the melting point of ice depend on pressure. This is not very convenient for standardizing the unit of measurement. Therefore, after the adoption of the kelvin K as the basic unit of temperature, the definition of the degree Celsius was revised.
According to the modern definition, a degree Celsius is equal to one kelvin K, and the zero of the Celsius scale is set so that the temperature of the triple point of water is 0.01 °C. As a result, the Celsius and Kelvin scales are shifted by 273.15:
26)Ideal gas- a mathematical model of a gas, in which it is assumed that the potential energy of the interaction of molecules can be neglected in comparison with their kinetic energy. The forces of attraction or repulsion do not act between molecules, the collisions of particles between themselves and with the walls of the vessel are absolutely elastic, and the time of interaction between molecules is negligibly small compared to the average time between collisions.
Where k is the Boltzmann constant (the ratio of the universal gas constant R to the number of Avogadro N A), i- the number of degrees of freedom of molecules (in most problems about ideal gases, where molecules are assumed to be spheres of small radius, the physical analogue of which can be inert gases), and T is the absolute temperature.
The basic equation of the MKT connects the macroscopic parameters (pressure, volume, temperature) of a gas system with the microscopic ones (molecular mass, average speed of their movement).
Russian State University of Innovation
technology and entrepreneurship
Penza branch
Department of natural sciences
abstract
In the discipline "Concepts of modern natural science"
Topic: "Model ideas about the structure of liquids, gases and crystals"
Completed by: student gr. 10E1 A. Antoshkina
Checked by: Associate Professor G. V. Surovitskaya
Penza 2010
Content
Introduction
Chapter 1
1.1. The concept of liquid
1.3 Liquid properties
Chapter 2. Gas
2.1. The concept of gas
2.2 Molecule movement
2.3 Gas properties
Chapter 3
3.1. The concept of crystals
3.2.types of crystal lattices
3.3. Properties of crystals, shape and syngony
Conclusion
Bibliography
Introduction
According to the sensations that various substances (bodies of substances) cause in the human senses, they can all be divided into three main groups: gaseous, liquid and crystalline (solid).
Gases do not have their own surface and their own volume. They completely occupy the vessel in which they are located. Gases have an unlimited ability to expand with increasing temperature and decreasing pressure. The distances between molecules in gases are many times greater than the dimensions of the molecules themselves, and the interactions between them, the so-called intermolecular interactions, are weak, and the molecules in a gas move almost independently of each other. The arrangement of particles in a gas is almost completely random (chaotic).
Crystals, like all solids, have a surface separating them from other solids, and a volume corresponding to it, which do not change (more precisely, change very slightly) in the gravitational field. The distances between particles in crystals are much smaller than in gases, and intermolecular or interatomic (if the crystal is built from atoms of one element) interactions are much stronger than in gases and liquids. Particles in a crystal are distributed in a fairly strict regular order, forming a crystal lattice. The particles that make up the crystal lattice are relatively firmly fixed in their places. A distinctive feature of crystals is that their properties are not the same in different directions. This phenomenon is called property anisotropy.
Liquids combine many of the properties of the gaseous and crystalline states. They have a surface and volume, which are affected by changes in the position of the vessel with liquid in the gravitational field. The liquid in the gravitational field occupies the lower part of the vessel in which it is located. Molecules in a liquid substance are interconnected by much stronger intermolecular forces than in a gas. The order in the arrangement of particles in liquid substances is also much higher than in gases. In some liquids, for example in water, some very small volumes have an order close to the order in crystals.
In the report, I tried to reveal the essence of each state of matter: liquid, gaseous and crystalline. She described the properties of substances, the arrangement of molecules and crystal lattices. Now let's take a closer look at each substance, representing it as a model.
Chapter 1
1.1 The concept of liquid
Each of us can easily recall many substances that he considers liquids. However, it is not so easy to give an exact definition of this state of matter. The liquid occupies, as it were, an intermediate position between a crystalline solid, characterized by complete order in the arrangement of its constituent particles (ions, atoms, molecules) and a gas, the molecules of which are in a state of chaotic (random) motion.
The shape of liquid bodies can be wholly or partly determined by the fact that their surface behaves like an elastic membrane. So, water can collect in drops. But the liquid is capable of flowing even under its immovable surface, and this also means that the form (of the internal parts of the liquid body) is not preserved.
The molecules of a liquid do not have a definite position, but at the same time, they do not have complete freedom of movement. There is an attraction between them, strong enough to keep them close. A substance in a liquid state exists in a certain temperature range, below which it passes into a solid state (crystallization occurs or transformation into a solid amorphous state - glass), above - into a gaseous state (evaporation occurs). The boundaries of this interval depend on pressure. As a rule, a substance in a liquid state has only one modification. (The most important exceptions are quantum liquids and liquid crystals.) Therefore, in most cases, a liquid is not only a state of aggregation, but also a thermodynamic phase (liquid phase). All liquids are usually divided into pure liquids and mixtures. Some mixtures of liquids are of great importance for life: blood, sea water, etc. Liquids can act as solvents.
1.2. Arrangement of molecules in a liquid
Molecules of a substance in a liquid state are located almost close to each other. Unlike solid crystalline bodies, in which molecules form ordered structures throughout the volume of the crystal and can perform thermal vibrations around fixed centers, liquid molecules have greater freedom. Each molecule of a liquid, as well as in a solid body, is “clamped” on all sides by neighboring molecules and performs thermal vibrations around a certain equilibrium position. However, from time to time any molecule can move to a nearby vacancy. Such jumps in liquids occur quite often; therefore, the molecules are not tied to certain centers, as in crystals, and can move throughout the entire volume of the liquid. This explains the fluidity of liquids. Due to the strong interaction between closely spaced molecules, they can form local (unstable) ordered groups containing several molecules. This phenomenon is called short-range order (Fig. 1).
Fig.1. an example of the short-range order of liquid molecules and the long-range order of molecules of a crystalline substance: 1.1 - water; 1. - ice.
Rice. 2. water vapor (1) and water (2). Water molecules are enlarged by about 5 x 107 times.
Figure 2 illustrates the difference between a gaseous substance and a liquid using water as an example. The H2O water molecule consists of one oxygen atom and two hydrogen atoms located at an angle of 104°. The average distance between vapor molecules is ten times greater than the average distance between water molecules. Unlike Fig. 1, where water molecules are shown as balls, Fig. 2 gives an idea of the structure of the water molecule. Due to the dense packing of molecules, the compressibility of liquids, i.e., the change in volume with a change in pressure, is very small; it is tens and hundreds of thousands of times less than in gases.
1.3 Liquid properties
Fluidity. Fluidity is the main property of liquids. If an external force is applied to a section of a fluid in equilibrium, then a flow of fluid particles occurs in the direction in which this force is applied: the fluid flows. Thus, under the action of unbalanced external forces, the liquid does not retain the shape and relative arrangement of the parts, and therefore takes the form of the vessel in which it is located. Unlike plastic solids, a liquid does not have a yield strength: it is enough to apply an arbitrarily small external force to make the liquid flow.
Preservation of volume. One of the characteristic properties of a liquid is that it has a certain volume (under constant external conditions). A liquid is extremely difficult to compress mechanically because, unlike a gas, there is very little free space between the molecules. The pressure produced on a liquid enclosed in a vessel is transmitted without change to each point of the volume of this liquid (Pascal's law is also valid for gases). This feature, along with very low compressibility, is used in hydraulic machines. Liquids typically increase in volume (expand) when heated and decrease in volume (contract) when cooled. However, there are exceptions, for example, water compresses when heated, at normal pressure and temperatures from 0 °C to approximately 4 °C.
Viscosity. In addition, liquids (like gases) are characterized by viscosity. It is defined as the ability to resist the movement of one of the parts relative to the other - that is, as internal friction. When adjacent layers of a liquid move relative to each other, a collision of molecules inevitably occurs in addition to that due to thermal motion. There are forces that slow down the ordered movement. At the same time, the kinetic energy of ordered movement turns into thermal energy - the energy of the chaotic movement of molecules. The liquid in the vessel, set in motion and left to itself, will gradually stop, but its temperature will rise.
Free surface formation and surface tension. Due to volume conservation, the liquid is able to form a free surface. Such a surface is the phase interface of a given substance: on one side is the liquid phase, on the other - the gaseous (steam), and possibly other gases, such as air. If the liquid and gaseous phases of the same substance are in contact, forces arise that tend to reduce the interface area - surface tension forces. The interface behaves like an elastic membrane that tends to shrink. Surface tension can be explained by the attraction between liquid molecules. Each molecule attracts other molecules, seeks to "surround" itself with them, and therefore, to leave the surface. Accordingly, the surface tends to decrease. Therefore, soap bubbles and bubbles during boiling tend to take on a spherical shape: for a given volume, a ball has a minimum surface. If only surface tension forces act on a liquid, it will necessarily take on a spherical shape - for example, water drops in weightlessness. Small objects with a density greater than the density of a liquid are able to "float" on the surface of the liquid, since the force of gravity is less than the force that prevents the increase in surface area. (See Surface tension.)
Evaporation and condensation. Evaporation is the gradual transition of a substance from a liquid to a gaseous phase (steam). During thermal motion, some molecules leave the liquid through its surface and turn into vapor. At the same time, some of the molecules pass back from the vapor to the liquid. If more molecules leave the liquid than come in, then evaporation takes place. Condensation is the reverse process, the transition of a substance from a gaseous state to a liquid state. In this case, more molecules pass from the vapor into the liquid than into the vapor from the liquid. Evaporation and condensation are non-equilibrium processes, they occur until local equilibrium is established (if established), and the liquid can completely evaporate, or come into equilibrium with its vapor, when as many molecules leave the liquid as return.
Boiling is the process of vaporization within a liquid. At a sufficiently high temperature, the vapor pressure becomes higher than the pressure inside the liquid, and vapor bubbles begin to form there, which (under the conditions of gravity) float to the top.
Wetting is a surface phenomenon that occurs when a liquid contacts a solid surface in the presence of steam, that is, at the interfaces of three phases. Wetting characterizes the “sticking” of a liquid to the surface and spreading over it (or, conversely, repulsion and not spreading). There are three cases: no wetting, limited wetting and complete wetting.
Miscibility is the ability of liquids to dissolve in each other. An example of miscible liquids: water and ethyl alcohol, an example of immiscible liquids: water and liquid oil.
Diffusion. When two miscible liquids are in a vessel, as a result of thermal motion, the molecules begin to gradually pass through the interface, and thus the liquids gradually mix. This phenomenon is called diffusion (it also occurs in substances in other states of aggregation).
Overheating and hypothermia. A liquid can be heated above the boiling point in such a way that boiling does not occur. This requires uniform heating, without significant temperature differences within the volume and without mechanical influences such as vibration. If something is thrown into a superheated liquid, it instantly boils. Superheated water is easy to get in the microwave. Subcooling - cooling of a liquid below the freezing point without turning into a solid state of aggregation. As with superheating, subcooling requires the absence of vibration and significant temperature fluctuations.
Coexistence with other phases. Formally speaking, for the equilibrium coexistence of a liquid phase with other phases of the same substance - gaseous or crystalline - strictly defined conditions are needed. So, at a given pressure, a strictly defined temperature is needed. Nevertheless, in nature and technology, everywhere liquid coexists with steam, or also with a solid state of aggregation - for example, water with water vapor and often with ice (if we consider steam as a separate phase present along with air). This is due to the following reasons:
- Non-equilibrium state. It takes time for the liquid to evaporate, until the liquid has completely evaporated, it coexists with the vapor. In nature, water is constantly evaporating, as well as the reverse process - condensation.
- closed volume. The liquid in a closed vessel begins to evaporate, but since the volume is limited, the vapor pressure rises, it becomes saturated even before the liquid has completely evaporated, if its amount was large enough. When the saturation state is reached, the amount of evaporated liquid is equal to the amount of condensed liquid, the system comes into equilibrium. Thus, in a limited volume, the conditions necessary for the equilibrium coexistence of liquid and vapor can be established.
- The presence of the atmosphere in the conditions of terrestrial gravity. Atmospheric pressure acts on a liquid (air and steam), while for steam, practically only its partial pressure should be taken into account. Therefore, the liquid and the vapor above its surface correspond to different points on the phase diagram, in the region of the existence of the liquid phase and in the region of the existence of the gaseous, respectively. This does not cancel evaporation, but evaporation takes time during which both phases coexist. Without this condition, liquids would boil and evaporate very quickly.
Chapter 2. Gas
2.1. The concept of gas
GAS is one of the aggregate states of a substance in which its constituent particles (atoms, molecules) are located at considerable distances from each other and are in free motion. Unlike a liquid and a solid, where the molecules are at close distances and are connected to each other by attractive and repulsive forces of considerable magnitude, the interaction of molecules in a gas manifests itself only in short moments of their approach (collision). In this case, there is a sharp change in the magnitude and direction of the velocity of the colliding particles.
The name "gas" comes from the Greek word "haos" and was introduced by Van Helmont at the beginning of the 17th century; it well reflects the true nature of the movement of particles in a gas, which is characterized by complete disorder and chaos. Unlike liquids, for example, gases do not form a free surface and uniformly fill the entire volume available to them. The gaseous state, if ionized gases are included, is the most common state of matter in the Universe (atmospheres of planets, stars, nebulae, interstellar matter, etc.).
2.2. Molecule movement
The motion of molecules in gases is random: the velocities of molecules do not have any preferred direction, but are distributed randomly in all directions. Due to the collisions of molecules with each other, their velocities change all the time both in direction and in absolute value. Therefore, the velocities of molecules can differ greatly from each other. At any moment in a gas there are molecules moving extremely fast and molecules moving relatively slowly. However, the number of molecules moving much slower or much faster than the others is small. The majority of molecules move at speeds that differ relatively little from some average speed, which depends on the type of molecules and the temperature of the body. In what follows, speaking of the speed of molecules, we will mean their average speed. We will turn to the question of measuring and calculating the average velocity of molecules later. In many discussions about the motion of gas molecules, the concept of the mean free path plays an important role. The mean free path is the average distance traveled by molecules between two successive collisions. As the gas density decreases, the mean free path increases. At atmospheric pressure and 0 ° C, the mean free path of air molecules is approximately 10-8-10-7 m (Fig. 371).
Rice. 371. This is approximately the path of an air molecule at normal pressure (increased a million times)
In very rarefied gases (for example, inside hollow electric light bulbs), the mean free path reaches several centimeters and even tens of centimeters. Here the molecules move from wall to wall almost without collision. Molecules in solids oscillate about average positions. In liquids, the molecules also oscillate around their average positions. However, from time to time each molecule jumps to a new middle position, several intermolecular distances away from the previous one.
2.3. Gas properties
In the gaseous state, the interaction energy of particles with each other is much less than their kinetic energy: EMMB<< Екин.
Therefore, gas molecules (atoms) are not held together, but move freely in a volume much larger than the volume of the particles themselves. The forces of intermolecular interaction are manifested when the molecules approach each other at a sufficiently close distance. Weak intermolecular interaction determines the low density of the gas, the desire for unlimited expansion, the ability to exert pressure on the walls of the vessel, preventing this desire. The gas molecules are in random chaotic motion, and there is no order in the gas with respect to the arrangement of the molecules. The state of the gas is characterized by: temperature - T, pressure - p and volume - V. At low pressures and high temperatures, all typical gases behave approximately the same. But already at ordinary and, especially, low temperatures and high pressures, the individualities of gases begin to appear. An increase in external pressure and a decrease in temperature bring gas particles closer together, so intermolecular interaction begins to manifest itself to a greater extent. For such gases, the Mendeleev-Clapeyron equation can no longer be applied: instead, the Van der Waals equation should be applied:
where a and b are constant terms, taking into account the presence of attractive forces between molecules and the intrinsic volume of molecules, respectively.
When gases are compressed, when there is a significant increase in their density, the IMF forces become more and more noticeable, which leads to the creation of conditions for the formation of various associates from molecules. Associates are relatively unstable groups of molecules. It follows from the nature of the MMW components that the universal forces of interaction increase with an increase in the size of atoms, the polarizability sharply increases, therefore, the heavier the particles of the same type (atoms or molecules) of a substance, the usually higher the degree of their association at a given temperature, the lower temperatures such a substance passes from gas to liquid.
Chapter 3
3.1. The concept of crystals
The world of crystals is a world no less beautiful, diverse, developing, often no less mysterious than the world of wildlife. The importance of crystals for the geological sciences lies in the fact that the vast majority of the earth's crust is in a crystalline state. In the classification of such fundamental objects of geology as mineral and rock, the concept of a crystal is primary, elementary, similar to an atom in the periodic system of elements or a molecule in the chemical classification of substances. According to the aphoristic statement of the famous mineralogist, professor of the St. Petersburg Mining Institute D.P. Grigoriev, "a mineral is a crystal". It is clear that the properties of minerals and rocks are closely related to the general properties of the crystalline state.
The word "crystal" is Greek (??????????), its original meaning is "ice". However, already in ancient times, this term was transferred to transparent natural polyhedra of other substances (quartz, calcite, etc.), since it was believed that this was also ice, which, for some reason, received stability at high temperatures. In Russian, this word has two forms: actually "crystal", meaning a naturally occurring polyhedral body, and "crystal" - a special kind of glass with a high refractive index, as well as transparent colorless quartz ("rock crystal"). In most European languages, the same word is used for both of these concepts (compare the English "Crystal Palace" - "Crystal Palace" in London and "Crystal Growth" - an international magazine on crystal growth).
Humanity got acquainted with crystals in ancient times. This is due, first of all, to their ability to self-cut, which is often realized in nature, that is, to spontaneously take the form of amazingly perfect polyhedra. Even a modern person, having encountered natural crystals for the first time, most often does not believe that these polyhedra are not the work of a skilled craftsman. The shape of crystals has long been given magical significance, as evidenced by some archaeological finds. References to "crystal" (apparently, after all, we are talking about "crystal") are repeatedly found in the Bible (see, for example: Revelation of John, 21, 11; 32, 1, etc.). Among mathematicians, there is a reasoned opinion that the prototypes of the five regular polyhedra (Plato's solids) were natural crystals. Many Archimedean (semi-regular) polyhedra also have exact or very close analogues in the world of crystals. And in the applied art of antiquity, crystal polyhedrons were sometimes used as role models, and even those that were obviously not considered by the science of that time. For example, in the State Hermitage there is a string of beads, the shape of which reproduces with high accuracy the characteristic shape of crystals of the beautiful semi-precious mineral garnet. These beads are made of gold (presumably, the Middle Eastern work of the 1st-5th centuries AD). Thus, crystals have long had a noticeable impact on the main areas of human interests: emotional (religion, art), ideological (religion), intellectual (science, art).
3.2. Main types of crystal lattices
In solids, atoms can be placed in space in two ways: 1) Random arrangement of atoms, when they do not occupy a certain place relative to each other. Such bodies are called amorphous. 2) An ordered arrangement of atoms, when atoms occupy quite definite places in space, Such substances are called crystalline.
Atoms oscillate relative to their average position with a frequency of about 1013 Hz. The amplitude of these oscillations is proportional to the temperature. Due to the ordered arrangement of atoms in space, their centers can be connected by imaginary straight lines. The set of such intersecting lines represents a spatial lattice, which is called a crystal lattice.
The outer electron orbits of the atoms are in contact, so that the packing density of atoms in the crystal lattice is very high. Crystalline solids consist of crystalline grains - crystallites. In adjacent grains, the crystal lattices are rotated relative to each other by a certain angle. In crystallites, short-range and long-range orders are observed. This means the presence of an ordered arrangement and stability of both the closest neighbors surrounding a given atom (short-range order) and atoms located at considerable distances from it up to the grain boundaries (long-range order).
a) b)
Rice. 1.1. Arrangement of atoms in crystalline (a) and amorphous (b) matter
Due to diffusion, individual atoms can leave their places in the nodes of the crystal lattice, however, in this case, the ordering of the crystal structure as a whole is not disturbed.
All metals are crystalline bodies having a certain type of crystal lattice, consisting of low-mobility positively charged ions, between which free electrons move (the so-called electron gas). This type of structure is called a metallic bond. The type of lattice is determined by the shape of an elementary geometric body, the multiple repetition of which along three spatial axes forms the lattice of a given crystalline body.
A) B)
C) D)
Rice. 1.2. The main types of crystal lattices of metals:
A) cubic (1 atom per cell)
B) body-centered cubic (bcc) (2 atoms per cell)
etc.................
The liquid occupies an intermediate position in properties and structure between gases and solid crystalline substances. Therefore, it has the properties of both gaseous and solid substances. In the molecular kinetic theory, different aggregate states of a substance are associated with different degrees of molecular order. For solids, the so-called long range order in the arrangement of particles, i.e. their orderly arrangement, repeating over long distances. In liquids, the so-called short range order in the arrangement of particles, i.e. their ordered arrangement, repeating at distances, is comparable with interatomic ones. At temperatures close to the crystallization temperature, the liquid structure is close to that of a solid. At high temperatures, close to the boiling point, the structure of the liquid corresponds to the gaseous state - almost all molecules participate in chaotic thermal motion.
Liquids, like solids, have a certain volume, and like gases, they take the shape of the vessel in which they are located. Gas molecules are practically not interconnected by the forces of intermolecular interaction, and in this case the average energy of the thermal motion of gas molecules is much greater than the average potential energy due to the forces of attraction between them, so the gas molecules scatter in different directions and the gas occupies the volume provided to it. In solid and liquid bodies, the forces of attraction between molecules are already significant and keep the molecules at a certain distance from each other. In this case, the average energy of the thermal motion of molecules is less than the average potential energy due to the forces of intermolecular interaction, and it is not enough to overcome the forces of attraction between molecules, so solids and liquids have a certain volume.
The pressure in liquids increases very sharply with increasing temperature and decreasing volume. The volumetric expansion of liquids is much less than that of vapors and gases, since the forces that bind molecules in a liquid are more significant; the same remark applies to thermal expansion.
The heat capacities of liquids usually increase with temperature (albeit slightly). The C p /C V ratio is practically equal to one.
The theory of fluid has not been fully developed to date. The development of a number of problems in the study of the complex properties of a liquid belongs to Ya.I. Frenkel (1894–1952). He explained the thermal motion in a liquid by the fact that each molecule oscillates for some time around a certain equilibrium position, after which it jumps to a new position, which is at a distance of the order of the interatomic distance from the initial one. Thus, the molecules of the liquid move quite slowly throughout the mass of the liquid. With an increase in the temperature of the liquid, the frequency of oscillatory motion increases sharply, and the mobility of molecules increases.
Based on the Frenkel model, it is possible to explain some distinctive features properties of the liquid. Thus, liquids, even near the critical temperature, have a much greater viscosity than gases, and the viscosity decreases with increasing temperature (rather than increases, as in gases). This is explained by a different nature of the momentum transfer process: it is transferred by molecules that jump from one equilibrium state to another, and these jumps become much more frequent with increasing temperature. Diffusion in liquids occurs only due to molecular jumps, and it occurs much more slowly than in gases. Thermal conductivity liquids is due to the exchange of kinetic energy between particles oscillating around their equilibrium positions with different amplitudes; sharp jumps of molecules do not play a noticeable role. The mechanism of heat conduction is similar to its mechanism in gases. A characteristic feature of a liquid is its ability to have free surface(not limited by solid walls).
