How to determine the state of matter. State of aggregation

Questions about what a state of aggregation is, what features and properties possess solids, liquids and gases are considered in several training courses. There are three classical states of matter, with their own characteristic features of the structure. Their understanding is an important point in comprehending the sciences of the Earth, living organisms, and production activities. These questions are studied by physics, chemistry, geography, geology, physical chemistry and other scientific disciplines. Substances that are under certain conditions in one of the three basic types of state can change with an increase or decrease in temperature or pressure. Let us consider possible transitions from one state of aggregation to another, as they are carried out in nature, technology and everyday life.

What is a state of aggregation?

The word of Latin origin "aggrego" in translation into Russian means "to attach". The scientific term refers to the state of the same body, substance. The existence of solids, gases and liquids at certain temperature values ​​and different pressures is characteristic of all the shells of the Earth. In addition to the three basic aggregate states, there is also a fourth. At elevated temperature and constant pressure, the gas turns into a plasma. To better understand what a state of aggregation is, it is necessary to remember the smallest particles that make up substances and bodies.

The diagram above shows: a - gas; b - liquid; c is a rigid body. In such figures, circles indicate the structural elements of substances. This is a symbol, in fact, atoms, molecules, ions are not solid balls. Atoms consist of a positively charged nucleus around which negatively charged electrons move at high speed. Knowledge of the microscopic structure of matter helps to better understand the differences that exist between different aggregate forms.

Ideas about the microworld: from Ancient Greece to the 17th century

The first information about the particles that make up physical bodies appeared in ancient Greece. Thinkers Democritus and Epicurus introduced such a concept as an atom. They believed that these smallest indivisible particles of different substances have a shape, certain sizes, are capable of movement and interaction with each other. Atomistics became the most advanced teaching of ancient Greece for its time. But its development slowed down in the Middle Ages. Since then scientists were persecuted by the Inquisition of the Roman Catholic Church. Therefore, until modern times, there was no clear concept of what the state of aggregation of matter is. Only after the 17th century did the scientists R. Boyle, M. Lomonosov, D. Dalton, A. Lavoisier formulate the provisions of the atomic-molecular theory, which have not lost their significance even today.

Atoms, molecules, ions - microscopic particles of the structure of matter

A significant breakthrough in understanding the microcosm occurred in the 20th century, when the electron microscope was invented. Taking into account the discoveries made by scientists earlier, it was possible to put together a harmonious picture of the microworld. Theories describing the state and behavior of the smallest particles of matter are quite complex, they belong to the field. To understand the features of different aggregate states of matter, it is enough to know the names and features of the main structural particles that form different substances.

1. Atoms are chemically indivisible particles. Preserved in chemical reactions, but destroyed in nuclear. Metals and many other substances of atomic structure have a solid state of aggregation under normal conditions.
2. Molecules are particles that are broken down and formed in chemical reactions. oxygen, water, carbon dioxide, sulfur. The state of aggregation of oxygen, nitrogen, sulfur dioxide, carbon, oxygen under normal conditions is gaseous.
3. Ions are charged particles that atoms and molecules turn into when they gain or lose electrons - microscopic negatively charged particles. Many salts have an ionic structure, for example, table salt, iron and copper sulfate.

There are substances whose particles are located in space in a certain way. The ordered mutual position of atoms, ions, molecules is called a crystal lattice. Usually ionic and atomic crystal lattices are typical for solids, molecular - for liquids and gases. Diamond has a high hardness. Its atomic crystal lattice is formed by carbon atoms. But soft graphite also consists of atoms of this chemical element. Only they are located differently in space. The usual state of aggregation of sulfur is a solid, but at high temperatures the substance turns into a liquid and an amorphous mass.

Substances in a solid state of aggregation

Solids under normal conditions retain their volume and shape. For example, a grain of sand, a grain of sugar, salt, a piece of rock or metal. If sugar is heated, the substance begins to melt, turning into a viscous brown liquid. Stop heating - again we get a solid. This means that one of the main conditions for the transition of a solid into a liquid is its heating or an increase in the internal energy of the particles of the substance. The solid state of aggregation of salt, which is used in food, can also be changed. But to melt table salt, you need a higher temperature than when heating sugar. The fact is that sugar consists of molecules, and table salt consists of charged ions, which are more strongly attracted to each other. Solids in liquid form do not retain their shape because the crystal lattices break down.

The liquid state of aggregation of the salt during melting is explained by the breaking of the bond between the ions in the crystals. Charged particles are released that can carry electrical charges. Molten salts conduct electricity and are conductors. In the chemical, metallurgical and engineering industries, solids are converted into liquids to obtain new compounds from them or give them different shapes. Metal alloys are widely used. There are several ways to obtain them, associated with changes in the state of aggregation of solid raw materials.

Liquid is one of the basic states of aggregation

If you pour 50 ml of water into a round bottom flask, you will notice that the substance immediately takes the form of a chemical vessel. But as soon as we pour the water out of the flask, the liquid will immediately spread over the surface of the table. The volume of water will remain the same - 50 ml, and its shape will change. These features are characteristic of the liquid form of the existence of matter. Liquids are many organic substances: alcohols, vegetable oils, acids.

Milk is an emulsion, that is, a liquid in which there are droplets of fat. A useful liquid mineral is oil. It is extracted from wells using drilling rigs on land and in the ocean. Sea water is also a raw material for industry. Its difference from the fresh water of rivers and lakes lies in the content of dissolved substances, mainly salts. During evaporation from the surface of water bodies, only H 2 O molecules pass into the vapor state, solutes remain. Methods for obtaining useful substances from sea water and methods for its purification are based on this property.

With complete removal of salts, distilled water is obtained. It boils at 100°C and freezes at 0°C. The brines boil and turn into ice at different temperatures. For example, water in the Arctic Ocean freezes at a surface temperature of 2°C.

The aggregate state of mercury under normal conditions is a liquid. This silver-gray metal is usually filled with medical thermometers. When heated, the column of mercury rises on the scale, the substance expands. Why is alcohol tinted with red paint used, and not mercury? This is explained by the properties of liquid metal. At 30-degree frosts, the state of aggregation of mercury changes, the substance becomes solid.

If the medical thermometer is broken and the mercury has spilled out, then it is dangerous to collect silver balls with your hands. It is harmful to inhale mercury vapor, this substance is very toxic. Children in such cases need to seek help from parents, adults.

gaseous state

Gases cannot retain their volume or shape. Fill the flask to the top with oxygen (its chemical formula is O 2). As soon as we open the flask, the molecules of the substance will begin to mix with the air in the room. This is due to Brownian motion. Even the ancient Greek scientist Democritus believed that the particles of matter are in constant motion. In solids, under normal conditions, atoms, molecules, ions do not have the opportunity to leave the crystal lattice, to free themselves from bonds with other particles. This is possible only when a large amount of energy is supplied from outside.

In liquids, the distance between particles is slightly greater than in solids; they require less energy to break intermolecular bonds. For example, the liquid aggregate state of oxygen is observed only when the gas temperature drops to −183 °C. At -223 ° C, O 2 molecules form a solid. When the temperature rises above the given values, oxygen turns into a gas. It is in this form that it is under normal conditions. At industrial enterprises, there are special installations for separating atmospheric air and obtaining nitrogen and oxygen from it. First, the air is cooled and liquefied, and then the temperature is gradually increased. Nitrogen and oxygen turn into gases under different conditions.

The Earth's atmosphere contains 21% oxygen and 78% nitrogen by volume. In liquid form, these substances are not found in the gaseous envelope of the planet. Liquid oxygen has a light blue color and is filled at high pressure into cylinders for use in medical facilities. In industry and construction, liquefied gases are necessary for many processes. Oxygen is needed for gas welding and cutting of metals, in chemistry - for the oxidation reactions of inorganic and organic substances. If you open the valve of an oxygen cylinder, the pressure decreases, the liquid turns into a gas.

Liquefied propane, methane and butane are widely used in energy, transport, industry and household activities. These substances are obtained from natural gas or during the cracking (splitting) of petroleum feedstock. Carbon liquid and gaseous mixtures play an important role in the economy of many countries. But oil and natural gas reserves are severely depleted. According to scientists, this raw material will last for 100-120 years. An alternative source of energy is air flow (wind). Fast-flowing rivers, tides on the shores of the seas and oceans are used to operate power plants.

Oxygen, like other gases, can be in the fourth state of aggregation, representing a plasma. An unusual transition from a solid to a gaseous state is a characteristic feature of crystalline iodine. A dark purple substance undergoes sublimation - turns into a gas, bypassing the liquid state.

How are transitions from one aggregate form of matter to another carried out?

Changes in the aggregate state of substances are not associated with chemical transformations, these are physical phenomena. When the temperature rises, many solids melt and turn into liquids. A further increase in temperature can lead to evaporation, that is, to the gaseous state of the substance. In nature and economy, such transitions are characteristic of one of the main substances on Earth. Ice, liquid, steam are the states of water under different external conditions. The compound is the same, its formula is H 2 O. At a temperature of 0 ° C and below this value, water crystallizes, that is, it turns into ice. When the temperature rises, the resulting crystals are destroyed - the ice melts, liquid water is again obtained. When it is heated, evaporation is formed - the transformation of water into gas - goes on even at low temperatures. For example, frozen puddles gradually disappear because the water evaporates. Even in frosty weather, wet clothes dry out, but this process is longer than on a hot day.

All the listed transitions of water from one state to another are of great importance for the nature of the Earth. Atmospheric phenomena, climate and weather are associated with the evaporation of water from the surface of the oceans, the transfer of moisture in the form of clouds and fog to land, precipitation (rain, snow, hail). These phenomena form the basis of the World water cycle in nature.

How do the aggregate states of sulfur change?

Under normal conditions, sulfur is bright shiny crystals or a light yellow powder, that is, it is a solid. The aggregate state of sulfur changes when heated. First, when the temperature rises to 190 ° C, the yellow substance melts, turning into a mobile liquid.

If you quickly pour liquid sulfur into cold water, you get a brown amorphous mass. With further heating of the sulfur melt, it becomes more and more viscous and darkens. At temperatures above 300 ° C, the state of aggregation of sulfur changes again, the substance acquires the properties of a liquid, becomes mobile. These transitions arise due to the ability of the atoms of the element to form chains of different lengths.

Why can substances be in different physical states?

The state of aggregation of sulfur - a simple substance - is solid under normal conditions. Sulfur dioxide is a gas, sulfuric acid is an oily liquid heavier than water. Unlike hydrochloric and nitric acids, it is not volatile; molecules do not evaporate from its surface. What state of aggregation has plastic sulfur, which is obtained by heating crystals?

In an amorphous form, the substance has the structure of a liquid, having a slight fluidity. But plastic sulfur simultaneously retains its shape (as a solid). There are liquid crystals that have a number of characteristic properties of solids. Thus, the state of matter under different conditions depends on its nature, temperature, pressure and other external conditions.

What are the features in the structure of solids?

The existing differences between the main aggregate states of matter are explained by the interaction between atoms, ions and molecules. For example, why does the solid aggregate state of matter lead to the ability of bodies to maintain volume and shape? In the crystal lattice of a metal or salt, structural particles are attracted to each other. In metals, positively charged ions interact with the so-called "electron gas" - the accumulation of free electrons in a piece of metal. Salt crystals arise due to the attraction of oppositely charged particles - ions. The distance between the above structural units of solids is much smaller than the size of the particles themselves. In this case, electrostatic attraction acts, it gives strength, and repulsion is not strong enough.

To destroy the solid state of aggregation of a substance, efforts must be made. Metals, salts, atomic crystals melt at very high temperatures. For example, iron becomes liquid at temperatures above 1538 °C. Tungsten is refractory and is used to make incandescent filaments for light bulbs. There are alloys that become liquid at temperatures above 3000 °C. Many on Earth are in a solid state. This raw material is extracted with the help of equipment in mines and quarries.

To detach even one ion from a crystal, it is necessary to expend a large amount of energy. But after all, it is enough to dissolve salt in water for the crystal lattice to disintegrate! This phenomenon is explained by the amazing properties of water as a polar solvent. H 2 O molecules interact with salt ions, destroying the chemical bond between them. Thus, dissolution is not a simple mixing of different substances, but a physical and chemical interaction between them.

How do the molecules of liquids interact?

Water can be liquid, solid and gas (steam). These are its main states of aggregation under normal conditions. Water molecules are made up of one oxygen atom with two hydrogen atoms bonded to it. There is a polarization of the chemical bond in the molecule, a partial negative charge appears on the oxygen atoms. Hydrogen becomes the positive pole in the molecule and is attracted to the oxygen atom of another molecule. This is called the "hydrogen bond".

The liquid state of aggregation is characterized by distances between structural particles comparable to their sizes. The attraction exists, but it is weak, so the water does not retain its shape. Vaporization occurs due to the destruction of bonds, which occurs on the surface of the liquid even at room temperature.

Are there intermolecular interactions in gases?

The gaseous state of a substance differs from liquid and solid in a number of parameters. Between the structural particles of gases there are large gaps, much larger than the size of the molecules. In this case, the forces of attraction do not work at all. The gaseous state of aggregation is characteristic of substances present in the composition of air: nitrogen, oxygen, carbon dioxide. In the figure below, the first cube is filled with a gas, the second with a liquid, and the third with a solid.

Many liquids are volatile; molecules of a substance break off from their surface and pass into the air. For example, if you bring a cotton swab dipped in ammonia to the opening of an open bottle of hydrochloric acid, white smoke appears. Right in the air, a chemical reaction occurs between hydrochloric acid and ammonia, ammonium chloride is obtained. What state of matter is this substance in? Its particles, which form white smoke, are the smallest solid crystals of salt. This experiment must be carried out under an exhaust hood, the substances are toxic.

Conclusion

The aggregate state of gas was studied by many outstanding physicists and chemists: Avogadro, Boyle, Gay-Lussac, Claiperon, Mendeleev, Le Chatelier. Scientists have formulated laws that explain the behavior of gaseous substances in chemical reactions when external conditions change. Open regularities not only entered the school and university textbooks of physics and chemistry. Many chemical industries are based on knowledge about the behavior and properties of substances in different states of aggregation.

Aggregate states of matter (from the Latin aggrego - I attach, I connect) - these are states of the same substance, the transitions between which correspond to abrupt changes in free energy, entropy, density and other physical parameters of the substance.

Gas (French gaz, derived from the Greek chaos - chaos) is an aggregate state of matter in which the interaction forces of its particles filling the entire volume provided to them are negligible. In gases, the intermolecular distances are large and the molecules move almost freely.

• Gases can be considered as highly superheated or low-saturated vapors.
• Above the surface of each liquid due to evaporation is vapor. When the vapor pressure rises to a certain limit, called the saturated vapor pressure, the evaporation of the liquid stops, since the pressure of the vapor and liquid becomes the same.
• A decrease in the volume of saturated steam causes some of the steam to condense, rather than an increase in pressure. Therefore, the vapor pressure cannot be higher than the saturation vapor pressure. The saturation state is characterized by the saturation mass contained in 1 m3 of saturated vapor mass, which depends on temperature. Saturated steam can become unsaturated if the volume is increased or the temperature is increased. If the temperature of the steam is much higher than the boiling point corresponding to a given pressure, the steam is called superheated.

Plasma A partially or fully ionized gas is called, in which the densities of positive and negative charges are almost the same. The sun, stars, clouds of interstellar matter are composed of gases - neutral or ionized (plasma). Unlike other states of aggregation, plasma is a gas of charged particles (ions, electrons) that electrically interact with each other at large distances, but do not have either short-range or long-range orders in the arrangement of particles.

Liquid - This is a state of aggregation of a substance, intermediate between solid and gaseous.

1. Liquids have some features of a solid (retains its volume, forms a surface, has a certain tensile strength) and a gas (takes the shape of the vessel in which it is located).
2. The thermal motion of molecules (atoms) of a liquid is a combination of small fluctuations around equilibrium positions and frequent jumps from one equilibrium position to another.
3. At the same time, slow movements of molecules and their oscillations inside small volumes occur, frequent jumps of molecules violate the long-range order in the arrangement of particles and cause the fluidity of liquids, and small oscillations around equilibrium positions cause the existence of short-range order in liquids.

Liquids and solids, unlike gases, can be regarded as highly condensed media. In them, molecules (atoms) are located much closer to each other and the interaction forces are several orders of magnitude greater than in gases. Therefore, liquids and solids have significantly limited possibilities for expansion, obviously cannot occupy an arbitrary volume, and at constant pressure and temperature they retain their volume, no matter in what volume they are placed. Transitions from a state of aggregation more ordered in structure to a less ordered one can also occur continuously. In this regard, instead of the concept of the state of aggregation, it is advisable to use a broader concept - the concept of phase.

phase is the totality of all parts of the system that have the same chemical composition and are in the same state. This is justified by the simultaneous existence of thermodynamically equilibrium phases in a multiphase system: a liquid with its own saturated vapor; water and ice at melting point; two immiscible liquids (a mixture of water with triethylamine), differing in concentration; the existence of amorphous solids that retain the structure of the liquid (amorphous state).

Amorphous solid state of matter is a kind of supercooled state of a liquid and differs from ordinary liquids by a significantly higher viscosity and numerical values ​​of kinetic characteristics.

Crystalline solid state of matter - this is a state of aggregation, which is characterized by large forces of interaction between the particles of a substance (atoms, molecules, ions). The particles of solids oscillate around the average equilibrium positions, called the nodes of the crystal lattice; the structure of these substances is characterized by a high degree of order (long-range and short-range order) - order in the arrangement (coordination order), in the orientation (orientation order) of structural particles, or order in physical properties (for example, in the orientation of magnetic moments or electric dipole moments). The region of existence of a normal liquid phase for pure liquids, liquid and liquid crystals is limited from the side of low temperatures by phase transitions, respectively, to the solid (crystallization), superfluid, and liquid-anisotropic state.

Everyone, I think, knows 3 basic aggregate states of matter: liquid, solid and gaseous. We encounter these states of matter every day and everywhere. Most often they are considered on the example of water. The liquid state of water is most familiar to us. We constantly drink liquid water, it flows from our tap, and we ourselves are 70% liquid water. The second aggregate state of water is ordinary ice, which we see on the street in winter. In gaseous form, water is also easy to meet in everyday life. In the gaseous state, water is, we all know, steam. It can be seen when we, for example, boil a kettle. Yes, it is at 100 degrees that water passes from a liquid state to a gaseous state.

These are the three aggregate states of matter familiar to us. But did you know that there are actually 4 of them? I think at least once everyone heard the word "plasma". And today I want you to also learn more about plasma - the fourth state of matter.

Plasma is a partially or fully ionized gas with the same density of both positive and negative charges. Plasma can be obtained from gas - from the 3rd state of matter by strong heating. The state of aggregation in general, in fact, completely depends on temperature. The first state of aggregation is the lowest temperature at which the body remains solid, the second state of aggregation is the temperature at which the body begins to melt and become liquid, the third state of aggregation is the highest temperature at which the substance becomes a gas. For each body, substance, the temperature of transition from one state of aggregation to another is completely different, for some it is lower, for some it is higher, but for everyone it is strictly in this sequence. And at what temperature does a substance become plasma? Since this is the fourth state, it means that the transition temperature to it is higher than that of each previous one. And indeed it is. In order to ionize a gas, a very high temperature is required. The lowest temperature and low ionized (about 1%) plasma is characterized by temperatures up to 100 thousand degrees. Under terrestrial conditions, such plasma can be observed in the form of lightning. The temperature of the lightning channel can exceed 30 thousand degrees, which is 6 times more than the surface temperature of the Sun. By the way, the Sun and all other stars are also plasma, more often still high-temperature. Science proves that about 99% of the entire matter of the Universe is plasma.

Unlike low-temperature plasma, high-temperature plasma has almost 100% ionization and temperatures up to 100 million degrees. This is truly stellar temperature. On Earth, such a plasma is found only in one case - for experiments on thermonuclear fusion. A controlled reaction is quite complex and energy-intensive, but an uncontrolled one has sufficiently proven itself as a weapon of colossal power - a thermonuclear bomb tested by the USSR on August 12, 1953.

Plasma is classified not only by temperature and degree of ionization, but also by density and quasi-neutrality. phrase plasma density usually means electron density, that is, the number of free electrons per unit volume. Well, with this, I think everything is clear. But not everyone knows what quasi-neutrality is. The quasi-neutrality of a plasma is one of its most important properties, which consists in the almost exact equality of the densities of its constituent positive ions and electrons. Due to the good electrical conductivity of the plasma, the separation of positive and negative charges is impossible at distances greater than the Debye length and at times greater than the period of plasma oscillations. Almost all plasma is quasi-neutral. An example of a non-quasi-neutral plasma is an electron beam. However, the density of non-neutral plasmas must be very low, otherwise they will quickly decay due to Coulomb repulsion.

We have considered very little terrestrial examples of plasma. But there are enough of them. Man has learned to use plasma for his own good. Thanks to the fourth aggregate state of matter, we can use gas discharge lamps, plasma TVs, electric arc welding, and lasers. Ordinary gas-discharge fluorescent lamps are also plasma. There is also a plasma lamp in our world. It is mainly used in science to study and, most importantly, to see some of the most complex plasma phenomena, including filamentation. A photo of such a lamp can be seen in the picture below:

In addition to household plasma devices, natural plasma can also often be seen on Earth. We have already talked about one of its examples. This is lightning. But in addition to lightning, plasma phenomena can be called the northern lights, "St. Elmo's fires", the Earth's ionosphere and, of course, fire.

Notice that both fire and lightning and other manifestations of plasma, as we call it, burn. What is the reason for such a bright emission of light by plasma? Plasma glow is due to the transition of electrons from a high-energy state to a low-energy state after recombination with ions. This process leads to radiation with a spectrum corresponding to the excited gas. This is why plasma glows.

I would also like to tell a little about the history of plasma. After all, once upon a time only such substances as the liquid component of milk and the colorless component of blood were called plasma. Everything changed in 1879. It was in that year that the famous English scientist William Crookes, investigating electrical conductivity in gases, discovered the phenomenon of plasma. True, this state of matter was called plasma only in 1928. And this was done by Irving Langmuir.

In conclusion, I want to say that such an interesting and mysterious phenomenon as ball lightning, which I wrote about more than once on this site, is, of course, also a plasmoid, like ordinary lightning. This is perhaps the most unusual plasmoid of all terrestrial plasma phenomena. After all, there are about 400 very different theories about ball lightning, but not one of them has been recognized as truly correct. Under laboratory conditions, similar but short-term phenomena have been obtained in several different ways, so the question of the nature of ball lightning remains open.

Ordinary plasma, of course, was also created in laboratories. Once it was difficult, but now such an experiment is not difficult. Since plasma has firmly entered our household arsenal, there are a lot of experiments on it in laboratories.

The most interesting discovery in the field of plasma was experiments with plasma in weightlessness. It turns out that plasma crystallizes in a vacuum. It happens like this: the charged particles of the plasma begin to repel each other, and when they have a limited volume, they occupy the space that is allotted to them, scattering in different directions. This is very similar to a crystal lattice. Doesn't this mean that plasma is the closing link between the first aggregate state of matter and the third? After all, it becomes a plasma due to the ionization of the gas, and in a vacuum, the plasma again becomes, as it were, solid. But that's just my guess.

Plasma crystals in space also have a rather strange structure. This structure can be observed and studied only in space, in a real space vacuum. Even if you create a vacuum on the Earth and place a plasma there, then gravity will simply squeeze the entire “picture” that forms inside. In space, however, plasma crystals simply take off, forming a volumetric three-dimensional structure of a strange shape. After sending the results of observations of plasma in orbit to earth scientists, it turned out that the swirls in the plasma mimic the structure of our galaxy in a strange way. And this means that in the future it will be possible to understand how our galaxy was born by studying plasma. The photographs below show the same crystallized plasma.

State of aggregation- a state of matter characterized by certain qualitative properties: the ability or inability to maintain volume and shape, the presence or absence of long-range and short-range order, and others. A change in the state of aggregation may be accompanied by a jump-like change in free energy, entropy, density, and other basic physical properties.
There are three main states of aggregation: solid, liquid and gas. Sometimes it is not entirely correct to classify plasma as a state of aggregation. There are other states of aggregation, for example, liquid crystals or Bose-Einstein condensate. Changes in the state of aggregation are thermodynamic processes called phase transitions. The following varieties are distinguished: from solid to liquid - melting; from liquid to gaseous - evaporation and boiling; from solid to gaseous - sublimation; from gaseous to liquid or solid - condensation; from liquid to solid - crystallization. A distinctive feature is the absence of a sharp boundary of the transition to the plasma state.
Aggregate state definitions are not always strict. So, there are amorphous bodies that retain the structure of a liquid and have little fluidity and the ability to retain shape; liquid crystals are fluid, but at the same time they have some properties of solids, in particular, they can polarize electromagnetic radiation passing through them. To describe various states in physics, a broader concept of a thermodynamic phase is used. Phenomena that describe transitions from one phase to another are called critical phenomena.
The aggregate state of a substance depends on the physical conditions in which it is located, mainly on temperature and pressure. The determining quantity is the ratio of the average potential energy of the interaction of molecules to their average kinetic energy. So, for a solid body this ratio is greater than 1, for gases it is less than 1, and for liquids it is approximately equal to 1. The transition from one state of aggregation of a substance to another is accompanied by an abrupt change in the value of this ratio, associated with an abrupt change in intermolecular distances and intermolecular interactions. In gases, the intermolecular distances are large, the molecules almost do not interact with each other and move almost freely, filling the entire volume. In liquids and solids - condensed media - molecules (atoms) are located much closer to each other and interact more strongly.
This leads to the preservation of liquids and solids of their volume. However, the nature of the movement of molecules in solids and liquids is different, which explains the difference in their structure and properties.
In solids in a crystalline state, atoms only vibrate near the nodes of the crystal lattice; the structure of these bodies is characterized by a high degree of order - long-range and short-range order. The thermal motion of molecules (atoms) of a liquid is a combination of small fluctuations around equilibrium positions and frequent jumps from one equilibrium position to another. The latter determine the existence in liquids of only short-range order in the arrangement of particles, as well as their inherent mobility and fluidity.
a. Solid- a state characterized by the ability to maintain volume and shape. Atoms of a solid body make only small vibrations around the state of equilibrium. There is both long-range and short-range order.
b. Liquid- a state of matter in which it has low compressibility, that is, it retains its volume well, but is not able to retain its shape. The liquid easily takes the shape of the vessel in which it is placed. Atoms or molecules of a liquid vibrate near the equilibrium state, locked by other atoms, and often jump to other free places. There is only short-range order.
Melting- this is the transition of a substance from a solid state of aggregation (see Aggregate states of matter) to a liquid. This process occurs during heating, when a certain amount of heat +Q is imparted to the body. For example, the low-melting metal lead passes from a solid state to a liquid state if it is heated to a temperature of 327 ° C. Lead easily melts on a gas stove, for example, in a stainless steel spoon (it is known that the flame temperature of a gas burner is 600-850 ° C, and the temperature melting of steel - 1300-1500°C).
If, while melting lead, its temperature is measured, then it can be found that at first it gradually increases, but after a certain moment it remains constant, despite further heating. This moment corresponds to melting. The temperature is held constant until all the lead has melted, and only then does it begin to rise again. When liquid lead is cooled, the opposite is observed: the temperature drops until solidification begins and remains constant all the time until the lead passes into the solid phase, and then decreases again.
All pure substances behave in the same way. The constancy of temperature during melting is of great practical importance, since it allows calibrating thermometers, making fuses and indicators that melt at a strictly specified temperature.
Atoms in a crystal vibrate about their equilibrium positions. As the temperature rises, the oscillation amplitude increases and reaches a certain critical value, after which the crystal lattice is destroyed. This requires additional thermal energy, so during the melting process the temperature does not rise, although heat continues to flow.
The melting point of a substance depends on pressure. For substances whose volume increases during melting (and the vast majority of them), an increase in pressure increases the melting point and vice versa. At water, the volume decreases during melting (therefore, when it freezes, water breaks pipes), and when pressure increases, ice melts at a lower temperature. Bismuth, gallium and some grades of cast iron behave in a similar way.
in. Gas- a condition characterized by good compressibility, the lack of the ability to maintain both volume and shape. Gas tends to occupy the entire volume provided to it. Atoms or molecules of a gas behave relatively freely, the distances between them are much greater than their size.
Plasma, often referred to as a state of aggregation of matter, differs from gas in a high degree of ionization of atoms. Most of the baryonic matter (by mass approx. 99.9%) in the Universe is in the plasma state.
g. C supercritical fluid- Occurs with a simultaneous increase in temperature and pressure to a critical point, at which the density of the gas is compared with the density of the liquid; in this case, the boundary between the liquid and gaseous phases disappears. The supercritical fluid has an exceptionally high dissolving power.
d. Bose-Einstein condensate- is obtained by cooling the Bose gas to temperatures close to absolute zero. As a result, some of the atoms are in a state with strictly zero energy (that is, in the lowest possible quantum state). The Bose-Einstein condensate exhibits a number of quantum properties such as superfluidity and Fischbach resonance.
e. Fermionic condensate- is a Bose-condensation in the BCS mode of "atomic Cooper pairs" in gases consisting of fermion atoms. (In contrast to the traditional mode of Bose-Einstein condensation of compound bosons).
Such fermionic atomic condensates are "relatives" of superconductors, but with a critical temperature of the order of room temperature and above.
Degenerate matter - Fermi gas 1st stage Electron degenerate gas, observed in white dwarfs, plays an important role in the evolution of stars. The 2nd stage is the neutron state where matter passes under ultrahigh pressure, which is unattainable in the laboratory yet, but exists inside neutron stars. During the transition to the neutron state, the electrons of matter interact with protons and turn into neutrons. As a result, matter in the neutron state consists entirely of neutrons and has a density of the order of nuclear. The temperature of the substance in this case should not be too high (in energy equivalent, not more than a hundred MeV).
With a strong increase in temperature (hundreds of MeV and above), in the neutron state, various mesons begin to be born and annihilate. With a further increase in temperature, deconfinement occurs, and the matter passes into the state of quark-gluon plasma. It no longer consists of hadrons, but of constantly born and disappearing quarks and gluons. Perhaps deconfinement occurs in two stages.
With a further unlimited increase in pressure without an increase in temperature, the matter collapses into a black hole.
With a simultaneous increase in both pressure and temperature, other particles are added to quarks and gluons. What happens to matter, space and time at temperatures close to the Planck temperature is still unknown.
Other states
During deep cooling, some (by no means all) substances pass into a superconducting or superfluid state. These states, of course, are separate thermodynamic phases, but they hardly deserve to be called new aggregate states of matter due to their non-universality.
Inhomogeneous substances such as pastes, gels, suspensions, aerosols, etc., which under certain conditions exhibit the properties of both solids and liquids and even gases, are usually classified as dispersed materials, and not to any specific aggregate states of matter .

Depending on temperature and pressure, any substance is capable of taking on various states of aggregation. Each such state is characterized by certain qualitative properties that remain unchanged within the framework of temperatures and pressures required for a given state of aggregation.

The characteristic properties of aggregate states include, for example, the ability of a body in a solid state to maintain its shape, or vice versa, the ability of a liquid body to change shape. However, sometimes the boundaries between different states of matter are quite blurred, as in the case of liquid crystals, or the so-called "amorphous bodies", which can be elastic like solids and fluid like liquids.

The transition between states of aggregation can occur with the release of free energy, changes in density, entropy, or other physical quantities. The transition from one state of aggregation to another is called a phase transition, and the phenomena accompanying such transitions are called critical phenomena.

List of known aggregate states