Type of crystal lattice of existing substances. Atomic, molecular, ionic and metallic crystal lattice

Topics of the USE codifier: Substances of molecular and non-molecular structure. Type of crystal lattice. The dependence of the properties of substances on their composition and structure.

Molecular Kinetic Theory

All molecules are made up of tiny particles called atoms. All currently discovered atoms are collected in the periodic table.

Atom is the smallest, chemically indivisible particle of a substance that retains its chemical properties. Atoms connect to each other chemical bonds. We have previously considered a. Be sure to study the theory on the topic: Types of chemical bonds, before studying this article!

Now let's look at how particles can combine in matter.

Depending on the location of the particles relative to each other, the properties of the substances they form can vary greatly. So, if the particles are located from each other long away(the distance between the particles is much greater than the size of the particles themselves), they practically do not interact with each other, they move randomly and continuously in space, then we are dealing with gas .

If the particles are located close to each other, but chaotically, more interact with each other, make intense oscillatory movements in one position, but can jump to another position, then this is a model of the structure liquids .

If the particles are located close to each other, but more orderly, and interact more among themselves, but move only within one equilibrium position, practically without moving to other position, we are dealing with solid .

Most known chemicals and mixtures can exist in solid, liquid and gaseous states. The simplest example is water. Under normal conditions, it liquid, at 0 o C it freezes - it passes from a liquid state to solid, and at 100 ° C it boils - goes into gas phase- water vapor. At the same time, many substances under normal conditions are gases, liquids or solids. For example, air, a mixture of nitrogen and oxygen, is a gas under normal conditions. But at high pressure and low temperature, nitrogen and oxygen condense and pass into the liquid phase. Liquid nitrogen is actively used in industry. Sometimes isolated plasma, as well as liquid crystals, as separate phases.

Many properties of individual substances and mixtures are explained by the mutual arrangement of particles in space relative to each other!

This article considers properties of solids, depending on their structure. Basic physical properties of solids: melting point, electrical conductivity, thermal conductivity, mechanical strength, plasticity, etc.

Melting temperature is the temperature at which a substance changes from solid to liquid and vice versa.

is the ability of a substance to deform without breaking.

Electrical conductivity is the ability of a substance to conduct current.

Current is the ordered movement of charged particles. Thus, current can be conducted only by substances in which there are moving charged particles. According to the ability to conduct current, substances are divided into conductors and dielectrics. Conductors are substances that can conduct current (i.e. contain mobile charged particles). Dielectrics are substances that practically do not conduct current.

In a solid, the particles of a substance can be located chaotically, or more orderly about. If the particles of a solid are located in space chaotically, the substance is called amorphous. Examples of amorphous substances - coal, mica glass.

If the particles of a solid are arranged in space in an orderly manner, i.e. form repeating three-dimensional geometric structures, such a substance is called crystal, and the structure itself crystal lattice . Most of the substances known to us are crystals. The particles themselves are located in nodes crystal lattice.

Crystalline substances are distinguished, in particular, by type of chemical bond between particles in a crystal - atomic, molecular, metallic, ionic; according to the geometric shape of the simplest cell of the crystal lattice - cubic, hexagonal, etc.

Depending on the type of particles forming a crystal lattice , distinguish atomic, molecular, ionic and metallic crystal structure .

Atomic crystal lattice

An atomic crystal lattice is formed when there are atoms. Atoms are connected to each other covalent chemical bonds. Accordingly, such a crystal lattice will be very durable, it is not easy to destroy it. An atomic crystal lattice can be formed by atoms with a high valency, i.e. with a large number of bonds with neighboring atoms (4 or more). As a rule, these are non-metals: simple substances - silicon, boron, carbon (allotropic modifications of diamond, graphite), and their compounds (borocarbon, silicon (IV) oxide, etc..). Since a predominantly covalent chemical bond occurs between non-metals, free electrons(as well as other charged particles) in substances with an atomic crystal lattice in most cases no. Therefore, these substances are usually conduct electricity very poorly, i.e. are dielectrics. These are general patterns, of which there are a number of exceptions.

Communication between particles in atomic crystals: .

At the nodes of the crystal with atomic crystal structure arranged atoms.

Phase state atomic crystals under normal conditions: as a rule, solids.

Substances, which form atomic crystals in the solid state:

1. Simple substances high valence (located in the middle of the periodic table): boron, carbon, silicon, etc.
2. Complex substances formed by these non-metals: silica (silicon oxide, quartz sand) SiO 2 ; silicon carbide (corundum) SiC; boron carbide, boron nitride, etc.

Physical properties of substances with an atomic crystal lattice:

— strength;

- refractoriness (high melting point);

- low electrical conductivity;

- low thermal conductivity;

— chemical inertness (inactive substances);

- insolubility in solvents.

Molecular crystal lattice is a lattice whose nodes are molecules. hold the molecules in the crystal weak forces of intermolecular attraction (van der Waals forces, hydrogen bonds, or electrostatic attraction). Accordingly, such a crystal lattice, as a rule, quite easy to destroy. Substances with a molecular crystal lattice - flimsy, fragile. The greater the force of attraction between molecules, the higher the melting point of the substance. As a rule, the melting points of substances with a molecular crystal lattice are not higher than 200-300K. Therefore, under normal conditions, most substances with a molecular crystal lattice exist in the form gases or liquids. The molecular crystal lattice, as a rule, is formed in solid form by acids, oxides of non-metals, other binary compounds of non-metals, simple substances that form stable molecules (oxygen O 2, nitrogen N 2, water H 2 O, etc.), organic substances. As a rule, these are substances with a covalent polar (rarely non-polar) bond. Because electrons are involved in chemical bonds, substances with a molecular crystal lattice - dielectrics, poor conductors of heat.

Communication between particles in molecular crystals: m intermolecular, electrostatic, or intermolecular forces of attraction.

At the nodes of the crystal with molecular crystal structure arranged molecules.

Phase state molecular crystals under normal conditions: gases, liquids and solids.

Substances, forming in the solid state molecular crystals:

1. Simple non-metal substances that form small, strong molecules (O 2 , N 2 , H 2 , S 8 and others);
2. Complex substances (compounds of non-metals) with covalent polar bonds (except for oxides of silicon and boron, compounds of silicon and carbon) - water H 2 O, sulfur oxide SO 3, etc.
3. Monatomic rare gases (helium, neon, argon, krypton and etc.);
4. Most organic substances that do not have ionic bonds — methane CH 4, benzene C 6 H 6, etc.

Physical properties substances with a molecular crystal lattice:

- fusibility (low melting point):

— high compressibility;

- molecular crystals in solid form, as well as in solutions and melts, do not conduct current;

- phase state under normal conditions - gases, liquids, solids;

— high volatility;

- low hardness.

Ionic crystal lattice

If there are charged particles at the nodes of the crystal - ions, we can talk about ionic crystal lattice . As a rule, with ionic crystals alternate positive ions(cations) and negative ions(anions), so the particles in the crystal are retained forces of electrostatic attraction . Depending on the type of crystal and the type of ions that form the crystal, such substances can be quite strong and tough. In the solid state, there are, as a rule, no mobile charged particles in ionic crystals. But when the crystal is dissolved or melted, the ions are released and can move under the action of an external electric field. Those. conduct current only solutions or melts ionic crystals. The ionic crystal lattice is characteristic of substances with ionic chemical bond. Examples such substances salt NaCl calcium carbonate- CaCO 3, etc. The ionic crystal lattice, as a rule, is formed in the solid phase salts, bases, as well as metal oxides and binary compounds of metals and non-metals.

Communication between particles in ionic crystals: .

At the nodes of the crystal with an ionic lattice ions.

Phase state ionic crystals under normal conditions: usually solids.

Chemical substances with an ionic crystal lattice:

1. Salts (organic and inorganic), including ammonium salts (for example, ammonium chloride NH4Cl);
2. grounds;
3. metal oxides;
4. Binary compounds containing metals and non-metals.

Physical properties of substances with an ionic crystal structure:

- high melting point (refractory);

- solutions and melts of ionic crystals - current conductors;

- most compounds are soluble in polar solvents (water);

- solid phase state in most compounds under normal conditions.

And, finally, metals are characterized by a special type of spatial structure - metal crystal lattice, which is due metallic chemical bond . Metal atoms hold valence electrons rather weakly. In a crystal formed by a metal, the following processes occur simultaneously: some atoms donate electrons and become positively charged ions; these electrons move randomly in the crystal; some of the electrons are attracted to the ions. These processes occur simultaneously and randomly. In this way, ions appear , as in the formation of an ionic bond, and common electrons are formed as in the formation of a covalent bond. Free electrons move randomly and continuously throughout the volume of the crystal, like a gas. Therefore, they are sometimes called electron gas ". Due to the presence of a large number of mobile charged particles, metals conduct electricity, heat. The melting point of metals varies greatly. Metals are also characterized peculiar metallic luster, malleability, i.e. the ability to change shape without destruction under strong mechanical stress, tk. chemical bonds are not broken.

Communication between particles : .

At the nodes of the crystal with metal grating metal ions and atoms.

Phase state metals under normal conditions: usually solids(exception - mercury, liquid under normal conditions).

Chemical substances with a metal crystal lattice - simple substances - metals.

Physical properties of substances with a metal crystal lattice:

– high thermal and electrical conductivity;

- malleability and plasticity;

- metallic luster;

— metals are generally insoluble in solvents;

Most metals are solids under normal conditions.

Comparison of the properties of substances with different crystal lattices

The type of crystal lattice (or the absence of a crystal lattice) makes it possible to evaluate the basic physical properties of a substance. For an approximate comparison of the typical physical properties of compounds with different crystal lattices, it is very convenient to use chemicals with characteristic properties. For a molecular lattice, for example, carbon dioxide, for the atomic crystal lattice - diamond, for metal - copper, and for the ionic crystal lattice - salt, sodium chloride NaCl.

A summary table on the structures of simple substances formed by chemical elements from the main subgroups of the periodic table (the elements of the secondary subgroups are metals, therefore, they have a metallic crystal lattice).

The final table of the relationship of the properties of substances with the structure:

One of the most common materials that people have always preferred to work with was metal. In each era, preference was given to different types of these amazing substances. So, IV-III millennia BC are considered to be the age of Chalcolith, or copper. Later it is replaced by bronze, and then the one that is still relevant today - iron comes into force.

Today it is generally difficult to imagine that it was once possible to do without metal products, because almost everything, from household items, medical instruments and ending with heavy and light equipment, consists of this material or includes separate parts from it. Why did metals manage to gain such popularity? What are the features and how it is inherent in their structure, let's try to figure it out further.

General concept of metals

"Chemistry. Grade 9" is a textbook used by schoolchildren. It is in it that metals are studied in detail. Consideration of their physical and chemical properties is devoted to a large chapter, because their diversity is extremely large.

It is from this age that it is recommended to give children an idea of ​​\u200b\u200bthese atoms and their properties, because adolescents can already fully appreciate the value of such knowledge. They perfectly see that the variety of objects, machines and other things that surround them is based on just a metallic nature.

What is a metal? From the point of view of chemistry, it is customary to refer to these atoms those that have:

• small at the external level;
• exhibit strong restorative properties;
• have a large atomic radius;
• how simple substances have a number of specific physical properties.

The basis of knowledge about these substances can be obtained by considering the atomic-crystalline structure of metals. It explains all the features and properties of these compounds.

In the periodic system, most of the entire table is allocated for metals, because they form all secondary subgroups and the main ones from the first to the third group. Therefore, their numerical superiority is obvious. The most common are:

• calcium;
• sodium;
• titanium;
• iron;
• magnesium;
• aluminum;
• potassium.

All metals have a number of properties that allow them to be combined into one large group of substances. In turn, these properties are explained precisely by the crystalline structure of metals.

Metal properties

The specific properties of the substances under consideration include the following.

1. Metallic sheen. All representatives of simple substances possess it, and most of them are the same. Only some (gold, copper, alloys) differ.
2. Malleability and plasticity - the ability to deform and recover quite easily. In different representatives it is expressed to a different extent.
3. Electrical and thermal conductivity is one of the main properties that determines the scope of the metal and its alloys.

The crystalline structure of metals and alloys explains the reason for each of the indicated properties and speaks of their severity in each specific representative. If you know the features of such a structure, then you can influence the properties of the sample and adjust it to the desired parameters, which people have been doing for many decades.

Atomic-crystalline structure of metals

What is such a structure, what is it characterized by? The name itself suggests that all metals are crystals in the solid state, that is, under normal conditions (except for mercury, which is a liquid). What is a crystal?

This is a conventional graphic image constructed by crossing imaginary lines through the atoms that line up the body. In other words, every metal is made up of atoms. They are located in it not randomly, but very regularly and consistently. So, if you mentally combine all these particles into one structure, you will get a beautiful image in the form of a regular geometric body of any shape.

This is called the crystal lattice of the metal. It is very complex and spatially voluminous, therefore, for simplicity, not all of it is shown, but only a part, an elementary cell. The set of such cells, brought together and reflected in and forms crystal lattices. Chemistry, physics and metal science are sciences that study the structural features of such structures.

Sama is a set of atoms that are located at a certain distance from each other and coordinate a strictly fixed number of other particles around them. It is characterized by the packing density, the distance between the constituent structures, and the coordination number. In general, all these parameters are a characteristic of the entire crystal, and therefore reflect the properties exhibited by the metal.

There are several varieties. They are all united by one feature - there are atoms in the nodes, and inside there is a cloud of electron gas, which is formed by the free movement of electrons inside the crystal.

Types of crystal lattices

Fourteen options for the structure of the lattice are usually combined into three main types. They are the following:

1. Body-centered cubic.
2. Hexagonal close-packed.
3. Face-centered cubic.

The crystal structure of metals was studied only when it became possible to obtain large magnifications of images. And the classification of the types of lattices was first introduced by the French scientist Bravais, by whose name they are sometimes called.

Body Centered Lattice

The structure of the crystal lattice of metals of this type is the following structure. This is a cube, at the nodes of which there are eight atoms. Another one is located in the center of the free internal space of the cell, which explains the name "body-centered".

This is one of the variants of the simplest structure of the elementary cell, and hence the entire lattice as a whole. The following metals are of this type:

• molybdenum;
• vanadium;
• chromium;
• manganese;
• alpha iron;
• beta iron and others.

The main properties of such representatives are a high degree of malleability and plasticity, hardness and strength.

face centered lattice

The crystal structure of metals having a face-centered cubic lattice is the following structure. This is a cube, which includes fourteen atoms. Eight of them form lattice nodes, and six more are located one on each face.

They have a similar structure:

• aluminum;
• nickel;
• lead;
• gamma iron;
• copper.

The main distinguishing properties are gloss of different colors, lightness, strength, malleability, increased resistance to corrosion.

Hexagonal lattice

The crystal structure of metals with lattices is as follows. The elementary cell is based on a hexagonal prism. There are 12 atoms in its nodes, two more at the bases and three atoms freely lie inside the space in the center of the structure. Only seventeen atoms.

Metals such as:

• alpha titanium;
• magnesium;
• alpha cobalt;
• zinc.

The main properties are a high degree of strength, a strong silvery sheen.

Defects in the crystal structure of metals

However, all considered types of cells can also have natural flaws, or so-called defects. This may be due to various reasons: foreign atoms and impurities in metals, external influences, and so on.

Therefore, there is a classification that reflects the defects that crystal lattices can have. Chemistry as a science studies each of them in order to identify the cause and remedy so that the properties of the material are not changed. So, the defects are as follows.

1. Point. They come in three main types: vacancies, impurities, or dislocated atoms. They lead to a deterioration in the magnetic properties of the metal, its electrical and thermal conductivity.
2. Linear, or dislocation. Allocate marginal and screw. Deteriorate the strength and quality of the material.
3. surface defects. They affect the appearance and structure of metals.

At present, methods have been developed for eliminating defects and obtaining pure crystals. However, it is not possible to completely eradicate them; the ideal crystal lattice does not exist.

The value of knowledge about the crystal structure of metals

From the above material, it is obvious that knowledge of the fine structure and structure makes it possible to predict the properties of the material and influence them. And this allows you to do the science of chemistry. The 9th grade of a general education school focuses on teaching students a clear understanding of the importance of the fundamental logical chain: composition - structure - properties - application.

Information about the crystal structure of metals very clearly illustrates and allows the teacher to clearly explain and show children how important it is to know the fine structure in order to correctly and competently use all properties.

In nature, there are two types of solids, which differ markedly in their properties. These are amorphous and crystalline bodies. And amorphous bodies do not have an exact melting point, they gradually soften during heating, and then turn into a fluid state. An example of such substances is resin or ordinary plasticine. But the situation is quite different with crystalline substances. They remain in a solid state up to a certain temperature, and only after reaching it, these substances melt.

It's all about the structure of such substances. In crystalline bodies, the particles of which they are composed are located at certain points. And if you connect them with straight lines, you get a kind of imaginary frame, which is called the crystal lattice. And the types of crystal lattices can be very different. And according to the type of particles from which they are “built”, lattices are divided into four types. These are ionic, atomic, molecular and

And at the nodes, respectively, there are ions, and between them there is an ionic bond. can be both simple (Cl-, Na+) and complex (OH-, SO2-). And these types of crystal lattices may contain some metal hydroxides and oxides, salts and other similar substances. Take, for example, ordinary sodium chloride. It alternates negative chlorine ions and positive sodium ions, which form a cubic crystal lattice. Ionic bonds in such a lattice are very stable, and substances “built” according to this principle have sufficiently high strength and hardness.

There are also types of crystal lattices called atomic. Here, atoms are located at the nodes, between which there is a strong covalent bond. Not many substances have an atomic lattice. These include diamond, as well as crystalline germanium, silicon and boron. There are some more complex substances that contain and have, respectively, an atomic crystal lattice. These are rock crystal and silica. And in most cases, such substances are very strong, hard and refractory. They are also practically insoluble.

And the molecular types of crystal lattices have a variety of substances. These include frozen water, that is, ordinary ice, "dry ice" - solidified carbon monoxide, as well as solid hydrogen sulfide and hydrogen chloride. Molecular lattices also have many solid organic compounds. These include sugar, glucose, naphthalene and other similar substances. And the molecules located in the nodes of such a lattice are interconnected by polar and non-polar chemical bonds. And despite the fact that there are strong covalent bonds between atoms inside the molecules, these molecules themselves are kept in the lattice due to very weak intermolecular bonds. Therefore, such substances are quite volatile, easily melted and do not have high hardness.

Well, metals have a variety of types of crystal lattices. And their nodes can contain both atoms and ions. At the same time, atoms can easily turn into ions, giving their electrons to the “general use”. In the same way, ions, "capturing" a free electron, can become atoms. And such a lattice determines such properties of metals as ductility, malleability, thermal and electrical conductivity.

Also, the types of crystal lattices of metals, and other substances, are divided into seven main systems according to the shape of the elementary cells of the lattice. The simplest is the cubic cell. There are also rhombic, tetragonal, hexagonal, rhombohedral, monoclinic, and triclinic unit cells that determine the shape of the entire crystal lattice. But in most cases, crystal lattices are more complex than those listed above. This is due to the fact that elementary particles can be located not only in the nodes of the lattice, but also in its center or on its faces. And among metals, the most common are three complex crystal lattices: face-centered cubic, body-centered cubic and hexagonal close-packed. The physical characteristics of metals also depend not only on the shape of their crystal lattice, but also on the interatomic distance and other parameters.

Solids exist in a crystalline and amorphous state and predominantly have a crystalline structure. It is distinguished by the correct location of particles at precisely defined points, is characterized by periodic repetition in volume. If we mentally connect these points with straight lines, we get a spatial frame, which is called the crystal lattice. The term "crystal lattice" refers to a geometric image that describes a three-dimensional periodicity in the arrangement of molecules (atoms, ions) in a crystal space.

The points where particles are located are called lattice nodes. Internodal connections operate inside the frame. The type of particles and the nature of the connection between them: molecules, atoms, ions - determine In total, four such types are distinguished: ionic, atomic, molecular and metallic.

If ions (particles with a negative or positive charge) are located at the lattice nodes, then this is an ionic crystal lattice characterized by bonds of the same name.

These bonds are very strong and stable. Therefore, substances with this type of structure have a sufficiently high hardness and density, non-volatile and refractory. At low temperatures, they behave as dielectrics. However, during the melting of such compounds, the geometrically correct ionic crystal lattice (the arrangement of ions) is violated and strength bonds decrease.

At a temperature close to the melting point, crystals with an ionic bond are already capable of conducting an electric current. Such compounds are readily soluble in water and other liquids that are composed of polar molecules.

The ionic crystal lattice is characteristic of all substances with an ionic type of bond - salts, metal hydroxides, binary compounds of metals with non-metals. has no direction in space, because each ion is associated with several counterions at once, the strength of interaction of which depends on the distance between them (Coulomb's law). Ionically bound compounds have a non-molecular structure, they are solids with ionic lattices, high polarity, high melting and boiling points, which are electrically conductive in aqueous solutions. Compounds with ionic bonds in their pure form are almost never found.

The ionic crystal lattice is inherent in some hydroxides and oxides of typical metals, salts, i.e. substances with ionic

In addition to ionic bonds in crystals, there are metallic, molecular and covalent bonds.

Crystals that have a covalent bond are semiconductors or dielectrics. Typical examples of atomic crystals are diamond, silicon and germanium.

Diamond is a mineral, an allotropic cubic modification (form) of carbon. The crystal lattice of diamond is atomic, very complex. At the nodes of such a lattice are atoms interconnected by extremely strong covalent bonds. A diamond is made up of individual carbon atoms, one at a time in the center of a tetrahedron whose vertices are the four closest atoms. Such a lattice is characterized by a face-centered cubic, which determines the maximum hardness of diamond and a rather high melting point. There are no molecules in the diamond lattice - and the crystal can be viewed as one imposing molecule.

In addition, it is characteristic of silicon, solid boron, germanium and compounds of individual elements with silicon and carbon (silica, quartz, mica, river sand, carborundum). In general, there are relatively few representatives with an atomic lattice.

In solids, particles (molecules, atoms, and ions) are located so close to each other that the forces of interaction between them do not allow them to fly apart. These particles can only make oscillatory motions around the equilibrium position. Therefore, solid bodies retain their shape and volume.

According to their molecular structure, solids are divided into crystalline and amorphous .

The structure of crystalline bodies

Crystal cell

Such solids are called crystalline, in which molecules, atoms or ions are arranged in a strictly defined geometric order, forming a structure in space, which is called crystal lattice . This order is periodically repeated in all directions in three-dimensional space. It persists over long distances and is not limited in space. He is called long-range order .

Types of crystal lattices

A crystal lattice is a mathematical model that can be used to represent how particles are arranged in a crystal. Mentally connecting in space with straight lines the points where these particles are located, we will get a crystal lattice.

The distance between atoms located at the nodes of this lattice is called lattice parameter .

Depending on which particles are located at the nodes, crystal lattices are molecular, atomic, ionic and metallic .

Such properties of crystalline bodies as melting point, elasticity, and strength depend on the type of crystal lattice.

When the temperature rises to a value at which the melting of the solid begins, the crystal lattice is destroyed. Molecules get more freedom, and the solid crystalline substance passes into the liquid stage. The stronger the bonds between molecules, the higher the melting point.

molecular lattice

In molecular lattices, bonds between molecules are not strong. Therefore, under normal conditions, such substances are in a liquid or gaseous state. The solid state for them is possible only at low temperatures. Their melting point (transition from solid to liquid) is also low. And under normal conditions, they are in a gaseous state. Examples are iodine (I 2), "dry ice" (carbon dioxide CO 2).

atomic lattice

In substances that have an atomic crystal lattice, the bonds between atoms are strong. Therefore, the substances themselves are very solid. They melt at high temperatures. Silicon, germanium, boron, quartz, oxides of some metals, and the hardest substance in nature, diamond, have a crystalline atomic lattice.

Ionic lattice

Substances with an ionic crystal lattice include alkalis, most salts, oxides of typical metals. Since the attractive force of ions is very high, these substances can only melt at very high temperatures. They are called refractory. They have high strength and hardness.

metal grate

At the nodes of the metal lattice, which all metals and their alloys have, both atoms and ions are located. Due to this structure, metals have good malleability and ductility, high thermal and electrical conductivity.

Most often, the shape of the crystal is a regular polyhedron. The faces and edges of such polyhedra always remain constant for a particular substance.

A single crystal is called single crystal . It has a regular geometric shape, a continuous crystal lattice.

Examples of natural single crystals are diamond, ruby, rock crystal, rock salt, Icelandic spar, quartz. Under artificial conditions, single crystals are obtained in the process of crystallization, when solutions or melts are cooled to a certain temperature and a solid substance in the form of crystals is isolated from them. With a slow crystallization rate, the faceting of such crystals has a natural shape. In this way, under special industrial conditions, for example, single crystals of semiconductors or dielectrics are obtained.

Small crystals, randomly fused with each other, are called polycrystals . The clearest example of a polycrystal is granite. All metals are also polycrystals.

Anisotropy of crystalline bodies

In crystals, particles are located with different densities in different directions. If we connect atoms in a straight line in one of the directions of the crystal lattice, then the distance between them will be the same in all this direction. In any other direction, the distance between the atoms is also constant, but its value may already differ from the distance in the previous case. This means that interaction forces of different magnitude act between atoms in different directions. Therefore, the physical properties of matter in these directions will also differ. This phenomenon is called anisotropy - the dependence of the properties of matter on direction.

Electrical conductivity, thermal conductivity, elasticity, refractive index and other properties of a crystalline substance differ depending on the direction in the crystal. Electric current is conducted differently in different directions, matter is heated differently, light rays are refracted differently.

Anisotropy is not observed in polycrystals. The properties of matter remain the same in all directions.