What is an aggregate state? Aggregate state of matter

Questions about what is the aggregate state, what features and properties are possessed by solids, liquids and gases are considered in several training courses. There are three classical states of matter, with their characteristic features of structure. Their understanding is an important moment in understanding the Earth sciences, living organisms, production activities. These issues are studied in 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 increasing or decreasing temperature and pressure. Let us consider possible transitions from one aggregate state to another, as they are carried out in nature, engineering and everyday life.

What is an aggregate state?

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

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

Representations about the microcosm: from ancient Greece to the 17th century

The first information about the particles, of which physical bodies are composed, appeared in Ancient Greece. The thinkers Democritus and Epicurus introduced such a concept as an atom. They believed that these smallest indivisible particles of different substances possess a shape, certain sizes, capable of movement and interaction with each other. Atomism has become the most advanced for its time the teachings of ancient Greece. But its development stalled in the Middle Ages. Since then the scholars were persecuted by the Inquisition of the Roman Catholic Church. Therefore, until the new time there was no intelligible concept of what an aggregate state of matter is. Only after the XVII century the scientists R. Boyle, M. Lomonosov, D. Dalton, A. Lavoisier formulated the positions of the atomic-molecular theory, which have not lost their significance even in our days.

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

A significant breakthrough in the understanding of the microworld occurred in the 20th century, when an electronic microscope was invented. Taking into account the discoveries made by scientists earlier, it was possible to lay down a harmonious picture of the microcosm. Theories describing the state and behavior of the smallest particles of matter are rather complex, they belong to the field of quantum physics. To understand the characteristics of different aggregate states of matter, it is sufficient 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 aggregate state under ordinary conditions.
2. Molecules are particles that are destroyed and formed in chemical reactions. Molecular structure has oxygen, water, carbon dioxide, sulfur. The aggregate state of oxygen, nitrogen, sulfur dioxide, carbon, oxygen under normal conditions is gaseous.
3. Ions are charged particles into which atoms and molecules are transformed when electrons are attached or lost-microscopic negatively charged particles. Ionic structure has many salts, for example, cookery, iron and copper sulfate.

There are substances whose particles are located in a certain way in space. The ordered mutual position of atoms, ions, molecules is called a crystal lattice. Usually, ionic and atomic crystal lattices are characteristic for solids, molecular lattices are for liquids and gases. Diamond is distinguished by 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 differently located in space. The usual aggregate state of sulfur is solid, but at high temperatures the substance becomes a liquid and an amorphous mass.

Substances in solid aggregate state

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

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

The liquid is one of the basic aggregate states

If you pour 50 ml of water into a round-bottomed flask, you can see that the substance immediately takes the form of a chemical vessel. But as soon as we pour water out of the flask, the liquid immediately spreads 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 existence of matter. Liquids are many organic substances: alcohols, vegetable oils, acids.

Milk is an emulsion, that is, a liquid in which droplets of fat are located. A useful liquid fossil is oil. Obtain it from wells with the help of 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 is the content of dissolved substances, mainly salts. When evaporation from the surface of reservoirs, only H ₂ O molecules pass to the vapor state, the dissolved substances remain. This method is based on the methods of obtaining useful substances from sea water and ways of cleaning it.

When the salts are completely removed, distilled water is obtained. It boils at 100 ° C, it freezes at 0 ° C. Brines boil and turn into ice at other 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 a scale, the substance is expanded. Why is it that street thermometers use alcohol, painted with red paint, and not mercury? This is explained by the properties of the liquid metal. At 30-degree frost, the aggregate state of mercury changes, the substance becomes solid.

If the medical thermometer crashed and the mercury spilled out, then collecting silvery balls is dangerous. Harmful to inhale vapors of mercury, this substance is very toxic. Children in such cases should seek help from parents and adults.

Gaseous state

Gases can not keep either 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. Ancient Greek scholar Democritus believed that the particles of matter are in constant motion. In solid bodies, under ordinary 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 large amounts of energy are supplied from outside.

In liquids, the distance between particles is slightly larger than in solids, they need less energy to break up 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. As the temperature rises above these values, oxygen is converted to gas. It is in this form that it is under ordinary conditions. In industrial plants, there are special facilities for separating air from the atmosphere and obtaining nitrogen and oxygen from it. First, the air is cooled and liquefied, and then the temperature is gradually increased. Nitrogen and oxygen are converted to gases under different conditions.

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

Liquefied propane, methane and butane find wide application in power engineering, transport, industry and household activities. These substances are obtained from natural gas or by cracking (splitting) of crude oil. Carbon liquid and gaseous mixtures play an important role in the economies of many countries. But the reserves of oil and natural gas are severely depleted. According to scientists, this raw material will last for 100-120 years. An alternative source of energy is air flow (wind). Used for the operation of power plants are fast flowing rivers, tides on the shores of the seas and oceans.

Oxygen, like other gases, can be in the fourth aggregate state, representing a plasma. An unusual transition from solid to gaseous state is a characteristic feature of crystalline iodine. A substance of dark purple color undergoes sublimation - it turns into gas, passing 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 related to chemical transformations, these are physical phenomena. When the temperature rises, many solids melt, 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 for one of the main substances on the Earth. Ice, liquid, steam - a state 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, the water crystallizes, that is, turns into ice. When the temperature rises, the crystals that arise are destroyed - ice melts, liquid water is again obtained. When it is heated, water vapor is formed. Evaporation - the transformation of water into a gas - goes even at low temperatures. For example, frozen puddles gradually disappear, because the water evaporates. Even in frosty weather, wet laundry dries up, but this process is longer than on a hot day.

All these 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 World Ocean, the transfer of moisture in the form of clouds and fog on land, precipitation (rain, snow, hail). These phenomena form the basis of the World water cycle in nature.

How do aggregate states of sulfur change?

Under normal conditions, sulfur is bright shiny crystals or a light yellow powder, i.e., it is a solid substance. The aggregate state of sulfur changes with heating. First, when the temperature is raised 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, darkening. At temperatures above 300 ° C, the aggregate state of sulfur changes again, the substance acquires fluid properties, 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?

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

In amorphous form, the substance has a liquid structure, with a slight fluidity. But plastic sulfur simultaneously retains its shape (as a solid substance). There are liquid crystals with 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 basic aggregate states of matter are explained by the interaction between atoms, ions and molecules. For example, why does the solid aggregate state of a substance lead to the ability of bodies to retain 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 a so-called "electron gas" - a cluster of free electrons in a piece of metal. Crystals of salts arise due to the attraction of unlike charged particles - ions. The distance between the above structural units of solids is much smaller than the dimensions of the particles themselves. In this case, electrostatic attraction acts, it imparts strength, and repulsion is not strong enough.

To destroy the solid aggregate state of the substance, one must make efforts. Metals, salts, atomic crystals melt at very high temperatures. For example, iron becomes liquid at a temperature above 1538 ° C. Refractory is tungsten, from which filaments are made for electric bulbs. There are alloys that become liquid at temperatures above 3000 ° C. Many rocks and minerals on Earth are in a solid state. Obtain this raw material with the help of technology in mines and quarries.

To detach even one ion from the crystal, it is necessary to expend a large amount of energy. But it's enough to dissolve the salt in the water, so that the crystal lattice breaks up! This phenomenon is explained by the surprising 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 physicochemical interaction between them.

How do molecules of liquids interact?

Water can be a liquid, a solid and a gas (steam). This is its basic aggregate state under normal conditions. The water molecules consist of one oxygen atom, to which two hydrogen atoms are bound. There is a polarization of the chemical bond in the molecule, a partial negative charge appears on the oxygen atoms. Hydrogen becomes a positive pole in the molecule, attracted by the oxygen atom of another molecule. This weak interaction was called the "hydrogen bond".

Liquid aggregate state characterizes distances between structural particles, comparable with their sizes. Attraction exists, but it is weak, so water does not retain 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 the substance differs from the liquid and solid in a number of parameters. Between the structural particles of gases there are large gaps, far exceeding the dimensions of the molecules. At the same time, the forces of attraction do not work at all. The gaseous aggregate state is characteristic of substances present in the air: nitrogen, oxygen, carbon dioxide. In the figure below, the first cube is filled with gas, the second liquid, and the third - with a solid.

Many liquids are volatile, the molecules of matter are torn from their surface and enter the air. For example, if you bring a cotton wool soaked in ammonia to an opening of an open bottle with hydrochloric acid, white smoke appears. Directly in air, a chemical reaction occurs between hydrochloric acid and ammonia, ammonium chloride is obtained. In what kind of aggregate is this substance? Its particles, forming white smoke, are the tiniest solid crystals of salt. This experience should be carried out under the hood, the substances are toxic.

Conclusion

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