Questions about what is the state of aggregation, what features and properties of 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 Earth sciences, living organisms, and production activities. Physics, chemistry, geography, geology, physical chemistry, and other scientific disciplines study these questions. Substances under certain conditions in one of the three basic types of state can change with increasing or decreasing temperature and pressure. Let us consider the possible transitions from one state of aggregation to another, as they occur in nature, technology and everyday life.
What is an aggregate state?
The word of Latin origin "aggrego" in translation into Russian means "attach". The scientific term refers to the state of the same body, substance. The existence at certain temperature values and different pressures of solids, gases and liquids 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. In order to better understand what an aggregate state is, it is necessary to recall the smallest particles of which substances and bodies consist.
The diagram above shows: a - gas; b is a liquid; c is a solid. In such figures, circles indicate the structural elements of substances. This symbol, in fact, atoms, molecules, ions are not continuous balls. Atoms consist of a positively charged nucleus, around which negatively charged electrons move at high speed. Knowledge of the microscopic structure of a substance helps to better understand the differences that exist between different aggregate forms.
Representations of the microworld: from Ancient Greece to the 17th century
The first information about the particles that make up physical bodies appeared in ancient Greece. The thinkers Democritus and Epicurus introduced the concept of atom. They believed that these smallest indivisible particles of different substances have a shape, a certain size, capable of movement and interaction with each other. Atomistics became the most advanced teaching of ancient Greece for its time. But its development was inhibited in the Middle Ages. Since then, scientists were pursued by the Inquisition of the Roman Catholic Church. Therefore, up to a new time, there was no clear concept of what the aggregate state of matter is. Only after the XVII century, scientists R. Boyle, M. Lomonosov, D. Dalton, A. Lavoisier formulated the provisions of atomic-molecular theory, which have not lost their significance in our days.
Atoms, molecules, ions - microscopic particles of the structure of matter
A significant breakthrough in understanding the microworld 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 that describe the state and behavior of the smallest particles of matter are quite complex; they relate to the field of quantum physics. To understand the characteristics of different aggregate states of matter, it is enough to know the names and characteristics of the main structural particles that form different substances.
- Atoms are chemically indivisible particles. Saved in chemical reactions, but destroyed in nuclear ones. Metals and many other substances of atomic structure have a solid state of aggregation under ordinary conditions.
- Molecules are particles that break down and form in chemical reactions. The molecular structure is oxygen, water, carbon dioxide, sulfur. The aggregate state of oxygen, nitrogen, sulfur dioxide, carbon, oxygen under ordinary conditions is gaseous.
- Ions - charged particles into which atoms and molecules turn when electrons attach or lose - microscopic negatively charged particles. Many salts have an ionic structure, for example, table, 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. Typically, ionic and atomic crystal lattices are characteristic of solids, molecular - for liquids and gases. Diamond is distinguished by its 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 state of aggregation of sulfur is solid, but at high temperatures the substance turns into a liquid and an amorphous mass.
Substances in the solid state of aggregation
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 the sugar is heated, then the substance begins to melt, turning into a viscous brown liquid. Stop heating - we get a solid again. So, one of the main conditions for the transition of a solid into a liquid is its heating or increase in the internal energy of the particles of the substance. The solid state of aggregation of salt 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 are destroyed.
The liquid state of aggregation of the salt during melting is explained by a break in the bond between the ions in the crystals. Charged particles that can carry electrical charges are released. Melts of salts conduct electricity, are conductors. In the chemical, metallurgical, and machine-building industries, solids are converted to liquids to form new compounds from them or to give them different shapes. Widespread metal alloys. 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 aggregate states
If you pour 50 ml of water into a round-bottom flask, you will notice that the substance will immediately take the form of a chemical vessel. But as soon as we pour water from 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. The listed features are characteristic of the liquid form of existence of matter. Liquids are many organic substances: alcohols, vegetable oils, acids.
Milk is an emulsion, i.e. the liquid in which droplets of fat are located. The useful liquid mineral is oil. They extract it 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 is in the content of dissolved substances, mainly salts. During evaporation from the surface of water bodies only H 2 O molecules pass into a vapor state, dissolved substances remain. This property is based on methods for obtaining useful substances from sea water and methods for its purification.
With complete removal of salts, distilled water is obtained. It boils at 100 ° C, freezes at 0 ° C. Brines boil and turn into ice at other temperature indicators. For example, water in the Arctic Ocean freezes at a surface temperature of 2 ° C.
The aggregate state of mercury under normal conditions is liquid. This silver gray metal is usually filled with medical thermometers. When heated, the column of mercury rises on a scale, the substance expands. Why is it that street thermometers use alcohol tinted in red and not mercury? This is explained by the properties of liquid metal. In 30-degree frosts, the state of aggregation of mercury changes, the substance becomes solid.
If the medical thermometer crashes and the mercury spills out, collecting silver balls with your hands is dangerous. It is harmful to inhale mercury vapor, this substance is very toxic. Children in such cases need to seek help from parents and adults.
Gaseous state
Gases are not able to maintain 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 particles of matter are in constant motion. In solids, under ordinary conditions, atoms, molecules, ions have no way to leave the crystal lattice, to free themselves from bonds with other particles. This is possible only when a large amount of energy comes from outside.
In liquids, the distance between particles is slightly larger than in solids; they require less energy to break intermolecular bonds. For example, the liquid state of aggregation of oxygen is observed only when the temperature of the gas decreases to −183 ° C. At −223 ° C, O 2 molecules form a solid. When the temperature rises above the given values, oxygen turns into gas. It is in this form that it is under ordinary conditions. Industrial enterprises have special facilities for separating atmospheric air and obtaining nitrogen and oxygen from it. First, the air is cooled and liquefied, and then the temperature is gradually raised. Nitrogen and oxygen turn into gases under different conditions.
The atmosphere of the Earth contains 21% by volume of oxygen and 78% of nitrogen. In liquid form, these substances are not found in the gas shell of the planet. Liquid oxygen has a light blue color, they are filled with cylinders at high pressure for use in medical institutions. In industry and construction, liquefied gases are necessary for conducting very 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 gas.
Liquefied propane, methane and butane are widely used in energy, 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 greatly depleted. According to scientists, this raw material is enough for 100-120 years. An alternative source of energy is airflow (wind). Fast-flowing rivers and tides on the shores of the seas and oceans are used for the operation of 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. The substance of dark purple color undergoes sublimation - it turns into gas, bypassing the liquid state.
How are the transitions from one aggregate form of matter to another?
Changes in the state of aggregation of substances are not associated with chemical transformations, these are physical phenomena. With increasing temperature, many solids melt, turn into liquids. A further increase in temperature can lead to evaporation, that is, to a gaseous state of the substance. In nature and in the economy, such transitions are characteristic of one of the main substances on Earth. Ice, liquid, steam are water conditions under various 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, turns into ice. With an increase in temperature, the crystals that have arisen are destroyed - the ice melts, and liquid water is obtained again. When it is heated, water vapor is formed. Evaporation - the conversion of water into gas - occurs even at low temperatures. For example, frozen puddles gradually disappear because the water evaporates. Even in frosty weather, wet clothes dry out, but only this process is longer than on a hot day.
All of these water transitions 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, rainfall (rain, snow, hail). These phenomena form the basis of the World Water Cycle in nature.
How do aggregate states of sulfur change?
Under ordinary 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 viscous, darkens. At temperatures above 300 ° C, the state of aggregation of sulfur changes again, the substance acquires the properties of a liquid and becomes mobile. These transitions arise due to the ability of atoms of an 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 ordinary conditions. Sulfur dioxide - gas, sulfuric acid - an oily liquid heavier than water. Unlike hydrochloric and nitric acids, it is not volatile; molecules do not evaporate from its surface. What is the state of aggregation of plastic sulfur, which is obtained by heating the crystals?
In an amorphous form, the substance has the structure of a liquid, having a slight fluidity. But plastic sulfur simultaneously retains its shape (like a solid). There are liquid crystals with a number of characteristic properties of solids. Thus, the state of a substance under different conditions depends on its nature, temperature, pressure, and other external conditions.
What are the features in the structure of solids?
The differences between the basic aggregate states of matter are explained by the interaction between atoms, ions and molecules. For example, why does the solid state of aggregation 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 the 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, from which incandescent filaments for light bulbs are made. There are alloys that become liquid at temperatures above 3000 ° C. Many rocks and minerals on Earth are in a solid state. This raw material is extracted using 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 water so that the crystal lattice breaks up! This phenomenon is explained by the amazing properties of water as a polar solvent. H 2 O molecules interact with salt ions, breaking the chemical bond between them. Thus, dissolution is not a simple mixing of different substances, but a physicochemical interaction between them.
How do liquid molecules interact?
Water can be liquid, solid, and gas (steam). These are its main state of aggregation under ordinary conditions. Water molecules consist of one oxygen atom, with which two hydrogen atoms are bonded. 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 is called the “hydrogen bond”.
The liquid state of aggregation is characterized by the distance between the structural particles, comparable with their size. Attraction exists, but it is weak, so water does not retain its shape. Vaporization occurs due to the destruction of bonds that occurs on the surface of a liquid even at room temperature.
Are there intermolecular interactions in gases?
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Many liquids are volatile, molecules of the substance come off from their surface and pass into the air. For example, if a cotton wool moistened with liquid ammonia is brought to the opening of an open bottle with hydrochloric acid, then white smoke appears. A chemical reaction takes place right in the air between hydrochloric acid and ammonia, and ammonium chloride is obtained. What aggregate state is this substance in? Its particles, forming white smoke, are tiny solid crystals of salt. This experiment must be carried out under the hood, the substances are toxic.
Conclusion
The aggregate state of the gas was studied by many prominent physicists and chemists: Avogadro, Boyle, Gay-Lussac, Klaiperon, Mendeleev, Le Chatelier. Scientists have formulated laws that explain the behavior of gaseous substances in chemical reactions when environmental conditions change. Open patterns not only entered 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.