When performing many physical and chemical reactions the substance passes into a solid state of aggregation. In this case, molecules and atoms tend to arrange themselves in such a spatial order in which the forces of interaction between particles of matter would be maximally balanced. This is how the strength of the solid substance is achieved. Atoms, once occupying a certain position, make small oscillatory movements, the amplitude of which depends on temperature, but their position in space remains fixed. The forces of attraction and repulsion balance each other at a certain distance.

Modern ideas about the structure of matter

Modern science states that an atom consists of a charged nucleus, which carries a positive charge, and electrons, which carry negative charges. At a speed of several thousand trillion revolutions per second, electrons rotate in their orbits, creating an electron cloud around the nucleus. The positive charge of the nucleus is numerically equal to the negative charge of the electrons. Thus, the atom of the substance remains electrically neutral. Possible interactions with other atoms occur when electrons are detached from their parent atom, thereby disturbing the electrical balance. In one case, the atoms line up in in a certain order, which is called the crystal lattice. In another, due to the complex interaction of nuclei and electrons, they combine into molecules various types and complexity.

Definition of crystal lattice

In total various types Crystal lattices of substances are networks with different spatial orientations, at the nodes of which ions, molecules or atoms are located. This stable geometric spatial position is called the crystal lattice of the substance. The distance between nodes of one crystal cell is called the identity period. The spatial angles at which the cell nodes are located are called parameters. According to the method of constructing bonds, crystal lattices can be simple, base-centered, face-centered, and body-centered. If the particles of matter are located only in the corners of the parallelepiped, such a lattice is called simple. An example of such a lattice is shown below:

If, in addition to the nodes, the particles of the substance are located in the middle of the spatial diagonals, then this arrangement of particles in the substance is called a body-centered crystal lattice. This type is clearly shown in the figure.

If, in addition to the nodes at the vertices of the lattice, there is a node at the place where the imaginary diagonals of the parallelepiped intersect, then you have a face-centered type of lattice.

Types of crystal lattices

The different microparticles that make up a substance determine the different types of crystal lattices. They can determine the principle of building connections between microparticles inside a crystal. Physical types of crystal lattices are ionic, atomic and molecular. This also includes various types of metal crystal lattices. Chemistry studies the principles of the internal structure of elements. The types of crystal lattices are presented in more detail below.

Ionic crystal lattices

These types of crystal lattices are present in compounds with an ionic type of bond. In this case, lattice sites contain ions with opposite electric charge. Thanks to the electromagnetic field, the forces of interionic interaction are quite strong, and this determines the physical properties of the substance. Common characteristics are refractoriness, density, hardness and the ability to conduct electric current. Ionic types crystal lattices are found in substances such as table salt, potassium nitrate and others.

Atomic crystal lattices

This type of structure of matter is inherent in elements whose structure is determined by covalent chemical bonds. Types of crystal lattices of this kind contain individual atoms at the nodes, connected to each other by strong covalent bonds. This type of bond occurs when two identical atoms “share” electrons, thereby forming a common pair of electrons for neighboring atoms. Thanks to this interaction, covalent bonds bind atoms evenly and strongly in a certain order. Chemical elements that contain atomic types of crystal lattices are hard, have a high melting point, are poor conductors of electricity, and are chemically inactive. Classic examples of elements with similar internal structure You can name diamond, silicon, germanium, boron.

Molecular crystal lattices

Substances that have a molecular type of crystal lattice are a system of stable, interacting, closely packed molecules that are located at the nodes of the crystal lattice. In such compounds, the molecules retain their spatial position in the gaseous, liquid and solid phases. At the nodes of the crystal, molecules are held together by weak van der Waals forces, which are tens of times weaker than the forces of ionic interaction.

The molecules that form a crystal can be either polar or nonpolar. Due to the spontaneous movement of electrons and vibrations of nuclei in molecules, the electrical equilibrium can shift - this is how an instantaneous electric dipole moment arises. Appropriately oriented dipoles create attractive forces in the lattice. Carbon dioxide and paraffin are typical examples of elements with a molecular crystal lattice.

Metal crystal lattices

A metal bond is more flexible and ductile than an ionic bond, although it may seem that both are based on the same principle. The types of crystal lattices of metals explain their typical properties - such as mechanical strength, thermal and electrical conductivity, and fusibility.

A distinctive feature of a metal crystal lattice is the presence of positively charged metal ions (cations) at the sites of this lattice. Between the nodes there are electrons that are directly involved in the creation electric field around the grate. The number of electrons moving around within this crystal lattice is called electron gas.

In the absence of an electric field, free electrons perform chaotic motion, randomly interacting with lattice ions. Each such interaction changes the momentum and direction of motion of the negatively charged particle. With their electric field, electrons attract cations to themselves, balancing their mutual repulsion. Although electrons are considered free, their energy is not enough to leave the crystal lattice, so these charged particles are constantly within its boundaries.

The presence of an electric field gives the electron gas additional energy. The connection with ions in the crystal lattice of metals is not strong, so electrons easily leave its boundaries. Electrons move along lines of force, leaving behind positively charged ions.

Conclusions

Chemistry attaches great importance to the study of the internal structure of matter. The types of crystal lattices of various elements determine almost the entire range of their properties. By influencing crystals and changing their internal structure, it is possible to enhance the desired properties of a substance and remove unwanted ones and transform chemical elements. Thus, studying internal structure the surrounding world can help to understand the essence and principles of the structure of the universe.

Crystalline substances

Solid crystals- three-dimensional formations characterized by strict repeatability of the same structural element ( unit cell) in all directions. The unit cell is the smallest volume of a crystal in the form of a parallelepiped, repeated in the crystal an infinite number of times.

The geometrically correct shape of crystals is determined, first of all, by their strictly regular internal structure. If, instead of atoms, ions or molecules in a crystal, we depict points as the centers of gravity of these particles, we get a three-dimensional regular distribution of such points, called a crystal lattice. The points themselves are called nodes crystal lattice.

Types of crystal lattices

Depending on what particles the crystal lattice is made of and what the nature chemical bond Between them, different types of crystals are distinguished.

Ionic crystals are formed by cations and anions (for example, salts and hydroxides of most metals). In them there is an ionic bond between the particles.

Ionic crystals may consist of monatomic ions. This is how crystals are built sodium chloride, potassium iodide, calcium fluoride.
The formation of ionic crystals of many salts involves monoatomic metal cations and polyatomic anions, for example, the nitrate ion NO 3? , sulfate ion SO 4 2? , carbonate ion CO 3 2? .

It is impossible to isolate single molecules in an ionic crystal. Each cation is attracted to each anion and repelled by other cations. The entire crystal can be considered a huge molecule. The size of such a molecule is not limited, since it can grow by adding new cations and anions.

Most ionic compounds crystallize in one of the structural types, which differ from each other in the value of the coordination number, that is, the number of neighbors around a given ion (4, 6 or 8). For ionic compounds with equal number cations and anions, four main types of crystal lattices are known: sodium chloride (the coordination number of both ions is 6), cesium chloride (the coordination number of both ions is 8), sphalerite and wurtzite (both structural types are characterized by the coordination number of the cation and anion equal to 4). If the number of cations is doubled less number anions, then the coordination number of cations should be twice the coordination number of anions. In this case, the structural types of fluorite (coordination numbers 8 and 4), rutile (coordination numbers 6 and 3), and cristobalite (coordination numbers 4 and 2) are realized.

Typically ionic crystals are hard but brittle. Their fragility is due to the fact that even with slight deformation of the crystal, cations and anions are displaced in such a way that the repulsive forces between like ions begin to prevail over the attractive forces between cations and anions, and the crystal is destroyed.

Ionic crystals have high melting points. In the molten state, the substances that form ionic crystals are electrically conductive. When dissolved in water, these substances dissociate into cations and anions, and the resulting solutions conduct electric current.

High solubility in polar solvents, accompanied by electrolytic dissociation, is due to the fact that in a solvent environment with a high dielectric constant, the energy of attraction between ions decreases. The dielectric constant of water is 82 times higher than that of vacuum (conditionally existing in an ionic crystal), and the attraction between ions in an aqueous solution decreases by the same amount. The effect is enhanced by solvation of ions.

Atomic crystals consist of individual atoms held together by covalent bonds. From simple substances Only boron and group IVA elements have such crystal lattices. Often, compounds of non-metals with each other (for example, silicon dioxide) also form atomic crystals.

Just like ionic crystals, atomic crystals can be considered giant molecules. They are very durable and hard, and do not conduct heat and electricity well. Substances that have atomic crystal lattices melt at high temperatures. They are practically insoluble in any solvents. They are characterized by low reactivity.

Molecular crystals are built from individual molecules, within which the atoms are connected by covalent bonds. Weaker intermolecular forces act between molecules. They are easily destroyed, so molecular crystals have low melting points, low hardness, and high volatility. Substances that form molecular crystal lattices do not have electrical conductivity, and their solutions and melts also do not conduct electric current.

Intermolecular forces arise due to the electrostatic interaction of the negatively charged electrons of one molecule with the positively charged nuclei of neighboring molecules. The strength of intermolecular interactions is influenced by many factors. The most important among them is the presence of polar bonds, that is, a shift in electron density from one atom to another. In addition, intermolecular interactions are stronger between molecules with a large number electrons.

Most nonmetals in the form of simple substances (for example, iodine I 2, argon Ar, sulfur S 8) and compounds with each other (for example, water, carbon dioxide, hydrogen chloride), as well as almost all solid organic matter form molecular crystals.

Metals are characterized by a metallic crystal lattice. It contains metal connection between atoms. In metal crystals, the nuclei of atoms are arranged in such a way that their packing is as dense as possible. The bonding in such crystals is delocalized and extends throughout the entire crystal. Metal crystals have high electrical and thermal conductivity, metallic luster and opacity, and easy deformability.

The classification of crystal lattices corresponds to limiting cases. Most crystals inorganic substances belongs to intermediate types - covalent-ionic, molecular-covalent, etc. For example, in a crystal graphite Within each layer, the bonds are covalent-metallic, and between the layers they are intermolecular.

Isomorphism and polymorphism

Many crystalline substances have the same structure. At the same time, the same substance can form different crystal structures. This is reflected in the phenomena isomorphism And polymorphism.

Isomorphism lies in the ability of atoms, ions or molecules to replace each other in crystal structures. This term (from the Greek " isos" - equal and " morphe" - form) was proposed by E. Mitscherlich in 1819. The law of isomorphism was formulated by E. Mitscherlich in 1821 in this way: “The same numbers of atoms, connected in the same way, give the same crystalline forms; Moreover, the crystalline form does not depend on the chemical nature of the atoms, but is determined only by their number and relative position.”

Working in the chemical laboratory of the University of Berlin, Mitscherlich drew attention to the complete similarity of the crystals of lead, barium and strontium sulfates and the similarity of the crystalline forms of many other substances. His observations attracted the attention of the famous Swedish chemist J.-Ya. Berzelius, who suggested that Mitscherlich confirm the observed patterns using the example of compounds of phosphoric and arsenic acids. As a result of the study, it was concluded that “the two series of salts differ only in that one contains arsenic as an acid radical, and the other contains phosphorus.” Mitscherlich's discovery very soon attracted the attention of mineralogists, who began research on the problem of isomorphic substitution of elements in minerals.

During the joint crystallization of substances prone to isomorphism ( isomorphic substances), mixed crystals (isomorphic mixtures) are formed. This is only possible if the particles replacing each other differ little in size (no more than 15%). In addition, isomorphic substances must have a similar spatial arrangement of atoms or ions and, therefore, similar in external form crystals. Such substances include, for example, alum. In crystals of potassium alum KAl(SO 4) 2. 12H 2 O potassium cations can be partially or completely replaced by rubidium or ammonium cations, and aluminum cations by chromium (III) or iron (III) cations.

Isomorphism is widespread in nature. Most minerals are isomorphic mixtures of complex, variable composition. For example, in the mineral sphalerite ZnS, up to 20% of zinc atoms can be replaced by iron atoms (while ZnS and FeS have different crystal structures). Isomorphism is associated with the geochemical behavior of rare and trace elements, their distribution in rocks and ores, where they are contained in the form of isomorphic impurities.

Isomorphic substitution determines many beneficial properties artificial materials modern technology- semiconductors, ferromagnets, laser materials.

Many substances can form crystalline forms that have different structures and properties, but the same composition ( polymorphic modifications). Polymorphism- the ability of solids and liquid crystals to exist in two or more forms with different crystal structures and properties with the same chemical composition. This word comes from the Greek " polymorphos"- diverse. The phenomenon of polymorphism was discovered by M. Klaproth, who in 1798 discovered that two different minerals - calcite and aragonite - have the same chemical composition CaCO 3.

Polymorphism of simple substances is usually called allotropy, while the concept of polymorphism does not apply to non-crystalline allotropic forms (for example, gaseous O 2 and O 3). A typical example of polymorphic forms is modifications of carbon (diamond, lonsdaleite, graphite, carbines and fullerenes), which differ sharply in properties. The most stable form of existence of carbon is graphite, however, its other modifications under normal conditions can persist indefinitely. At high temperatures they turn into graphite. In the case of diamond, this occurs when heated above 1000 o C in the absence of oxygen. The reverse transition is much more difficult to achieve. Not only high temperature is required (1200-1600 o C), but also enormous pressure - up to 100 thousand atmospheres. The transformation of graphite into diamond is easier in the presence of molten metals (iron, cobalt, chromium and others).

In the case of molecular crystals, polymorphism manifests itself in different packing of molecules in the crystal or in changes in the shape of molecules, and in ionic crystals - in different relative position cations and anions. Some simple and complex substances have more than two polymorphs. For example, silicon dioxide has ten modifications, calcium fluoride - six, ammonium nitrate - four. Polymorphic modifications are usually denoted Greek letters b, c, d, e, f,… starting with modifications that are stable at low temperatures.

When crystallizing from steam, solution or melt a substance that has several polymorphic modifications, a modification that is less stable under given conditions is first formed, which then turns into a more stable one. For example, when phosphorus vapor condenses, white phosphorus is formed, which under normal conditions slowly turns into red phosphorus when heated. When lead hydroxide is dehydrated, at first (about 70 o C) yellow b-PbO, which is less stable at low temperatures, is formed; at about 100 o C it turns into red b-PbO, and at 540 o C it turns back into b-PbO.

The transition from one polymorph to another is called polymorphic transformation. These transitions occur when temperature or pressure changes and are accompanied by an abrupt change in properties.

The process of transition from one modification to another can be reversible or irreversible. Thus, when a white soft graphite-like substance of composition BN (boron nitride) is heated at 1500-1800 o C and a pressure of several tens of atmospheres, its high-temperature modification is formed - Borazon, close to diamond in hardness. When the temperature and pressure are lowered to values ​​corresponding to normal conditions, borazone retains its structure. An example of a reversible transition is the mutual transformations of two modifications of sulfur (orthorhombic and monoclinic) at 95 o C.

Polymorphic transformations can occur without significant changes in structure. Sometimes there is no change in the crystal structure at all, for example, during the transition of b-Fe to c-Fe at 769 o C, the structure of iron does not change, but its ferromagnetic properties disappear.

Chemical-thermal treatment (CHT) is called heat treatment, consisting in a combination of thermal and chemical exposure in order to change the composition, structure and properties of the surface layer of steel.

Chemical-thermal treatment is one of the most common types of processing of materials in order to impart operational properties to them. The most widely used methods are saturation of the surface layer of steel with carbon and nitrogen, both separately and together. These are the processes of carburization (carburization) of the surface, nitriding - saturation of the steel surface with nitrogen, nitrocarburization and cyanidation - the joint introduction of carbon and nitrogen into the surface layers of steel. Saturation of the surface layers of steel with other elements (chrome - diffusion chrome plating, boron - boriding, silicon - silicon plating and aluminum - aluminizing) is used much less frequently. The process of diffusion saturation of the surface of a part with zinc is called galvanizing, and with titanium - titanation.

The chemical-thermal treatment process is a multi-stage process that includes three successive stages:

1. Formation of active atoms in a saturating environment near the surface or directly on the surface of the metal. The power of the diffusion flow, i.e. the number of active atoms formed per unit time depends on the composition and state of aggregation of the saturating medium, which can be solid, liquid or gaseous, the interaction of individual components with each other, temperature, pressure and chemical composition steel.

2. Adsorption (sorption) of the formed active atoms by the saturation surface. Adsorption is a complex process that occurs on the saturation surface in a non-stationary manner. A distinction is made between physical (reversible) adsorption and chemical adsorption (chemisorption). During chemical-thermal treatment, these types of adsorption overlap each other. Physical adsorption leads to the adhesion of adsorbed atoms of the saturating element (adsorbate) to the formed surface (adsorbent) due to the action of van der Waals forces of attraction, and it is characterized by easy reversibility of the adsorption process - desorption. During chemisorption, an interaction occurs between the atoms of the adsorbate and the adsorbent, which is close to chemical in nature and strength.

3. Diffusion - movement of adsorbed atoms in the lattice of the metal being processed. The diffusion process is possible only if there is solubility of the diffusing element in the material being processed and a sufficiently high temperature to provide the energy necessary for the process to occur. The thickness of the diffusion layer, and therefore the thickness of the hardened layer of the surface of the product, is the most important characteristic of chemical-thermal treatment. The thickness of the layer is determined by a number of factors such as saturation temperature, duration of the saturation process, steel composition, i.e. the content of certain alloying elements in it, the concentration gradient of the saturated element between the surface of the product and in the depth of the saturated layer.

The cutting tool operates under conditions of prolonged contact and friction with the metal being processed. During operation, the configuration and properties of the cutting edge must remain unchanged. The material for the manufacture of cutting tools must have high hardness (IKS 60-62) and wear resistance, i.e. ability long time maintain the cutting properties of the edge under friction conditions.

The greater the hardness of the processed materials, the thicker the chips and the higher the cutting speed, the greater the energy spent on the cutting process. Mechanical energy turns into thermal energy. The generated heat heats the cutter, the workpiece, and the chips and is partially dissipated. Therefore, the main requirement for tool materials is high heat resistance, i.e. the ability to maintain hardness and cutting properties during prolonged heating during operation. Based on heat resistance, there are three groups of tool steels for cutting tools: non-heat-resistant, semi-heat-resistant and heat-resistant.

When non-heat-resistant steels are heated to 200-300°C during the cutting process, carbon is released from the hardening martensite and coagulation of cementite-type carbides begins. This leads to loss of hardness and wear resistance of the cutting tool. Non-heat-resistant steels include carbon and low-alloy steels. Semi-heat-resistant steels, which include some medium-alloy steels, for example 9Kh5VF, retain hardness up to temperatures of 300-500°C. Heat-resistant steels retain their hardness and wear resistance when heated to temperatures of 600°C.

Carbon and low-alloy steels have relatively low heat resistance and low hardenability, so they are used for easier working conditions at low cutting speeds. High-speed steels, which have higher heat resistance and hardenability, are used for more severe working conditions. Carbide and ceramic materials allow even higher cutting speeds. Of the existing materials, boron nitride, elbor, has the greatest heat resistance. Elbor allows the processing of high-hardness materials, such as hardened steel, at high speeds.

Most solids have a crystalline structure. Crystal lattice built from repeating identical structural units, individual for each crystal. This structural unit is called the “unit cell”. In other words, the crystal lattice serves as a reflection of the spatial structure of a solid.

Crystal lattices can be classified in different ways.

I. According to the symmetry of crystals lattices are classified into cubic, tetragonal, rhombic, hexagonal.

This classification is convenient for assessing the optical properties of crystals, as well as their catalytic activity.

II. By the nature of the particles, located at lattice nodes and by type of chemical bond there is a distinction between them atomic, molecular, ionic and metal crystal lattices. The type of bond in a crystal determines the difference in hardness, solubility in water, the magnitude of the heat of solution and heat of fusion, and electrical conductivity.

Important characteristic crystal is crystal lattice energy, kJ/mol – the energy that must be expended to destroy a given crystal.

Molecular lattice

Molecular crystals consist of molecules held in certain positions of the crystal lattice by weak intermolecular bonds (van der Waals forces) or hydrogen bonds. These lattices are characteristic of substances with covalent bonds.

There are a lot of substances with a molecular lattice. This large number organic compounds(sugar, naphthalene, etc.), crystalline water (ice), solid carbon dioxide(“dry ice”), solid hydrogen halides, iodine, solid gases, including noble ones,

The energy of the crystal lattice is minimal for substances with non-polar and low-polar molecules (CH 4, CO 2, etc.).

Lattices formed by more polar molecules also have a higher crystal lattice energy. The greatest energy is possessed by lattices containing substances that form hydrogen bonds(H 2 O, NH 3).

Due to the weak interaction between molecules, these substances are volatile, fusible, have low hardness, do not conduct electric current (dielectrics) and have low thermal conductivity.

Atomic lattice

In nodes atomic crystal lattice there are atoms of one or different elements connected to each other by covalent bonds along all three axes. Such crystals which are also called covalent, are relatively few in number.

Examples of crystals of this type include diamond, silicon, germanium, tin, and also crystals complex substances, such as boron nitride, aluminum nitride, quartz, silicon carbide. All these substances have a diamond-like lattice.

The energy of the crystal lattice in such substances practically coincides with the energy of the chemical bond (200 – 500 kJ/mol). This determines their physical properties: high hardness, melting point and boiling point.

The electrically conductive properties of these crystals are varied: diamond, quartz, boron nitride are dielectrics; silicon, germanium – semiconductors; Metallic gray tin conducts electricity well.

In crystals with an atomic crystal lattice, it is impossible to distinguish a separate structural unit. The entire single crystal is one giant molecule.

Ionic lattice

In nodes ionic lattice positive and negative ions alternate, between which electrostatic forces act. Ionic crystals form compounds with ionic bonds, for example, sodium chloride NaCl, potassium fluoride and KF, etc. Ionic compounds may also include complex ions, for example, NO 3 -, SO 4 2 -.

Ionic crystals are also a giant molecule in which each ion is significantly influenced by all other ions.

The energy of the ionic crystal lattice can reach significant values. So, E (NaCl) = 770 kJ/mol, and E (BeO) = 4530 kJ/mol.

Ionic crystals have high melting and boiling points and high strength, but are brittle. Many of them conduct electricity poorly when room temperature(about twenty orders of magnitude lower than that of metals), but with increasing temperature an increase in electrical conductivity is observed.

Metal grate

Metal crystals give examples of the simplest crystal structures.

Metal ions in the lattice of a metal crystal can be approximately considered in the form of spheres. IN hard metals these balls are packed with maximum density, as indicated by the significant density of most metals (from 0.97 g/cm 3 for sodium, 8.92 g/cm 3 for copper to 19.30 g/cm 3 for tungsten and gold). The most dense packing of balls in one layer is a hexagonal packing, in which each ball is surrounded by six other balls (in the same plane). The centers of any three adjacent balls form an equilateral triangle.

Properties of metals such as high ductility and malleability indicate a lack of rigidity in metal gratings: their planes move quite easily relative to each other.

Valence electrons participate in the formation of bonds with all atoms and move freely throughout the entire volume of a piece of metal. This is indicated high values electrical conductivity and thermal conductivity.

In terms of crystal lattice energy, metals occupy an intermediate position between molecular and covalent crystals. The energy of the crystal lattice is:

Thus, the physical properties of solids depend significantly on the type of chemical bond and structure.

Structure and properties of solids

Characteristics	Crystals
Metal	Ionic	Molecular	Atomic
Examples	K, Al, Cr, Fe	NaCl, KNO3	I 2, naphthalene	diamond, quartz
Structural particles	Positive ions and mobile electrons	Cations and anions	Molecules	Atoms
Type of chemical bond	Metal	Ionic	In molecules – covalent; between molecules - van der Waals forces and hydrogen bonds	Between atoms - covalent
t melting	High	High	Low	Very high
boiling point	High	High	Low	Very high
Mechanical properties	Hard, malleable, viscous	Hard, brittle	Soft	Very hard
Electrical conductivity	Good guides	In solid form - dielectrics; in a melt or solution - conductors	Dielectrics	Dielectrics (except graphite)
Solubility
in the water	Insoluble	Soluble	Insoluble	Insoluble
in non-polar solvents	Insoluble	Insoluble	Soluble	Insoluble

(All definitions, formulas, graphs and equations of reactions are given on record.)

According to Boyle's atomic-molecular theory, all substances consist of molecules that are in constant movement. But is there any specific structure in substances? Or are they simply made up of randomly moving molecules?

In fact, all substances that are in the atmosphere have a clear structure. solid state. Atoms and molecules move, but the forces of attraction and repulsion between particles are balanced, so atoms and molecules are located at a certain point in space (but continue to make small fluctuations depending on temperature). Such structures are called crystal lattices. The places in which the molecules, ions or atoms themselves are located are called nodes. And the distances between the nodes are called - periods of identity. Depending on the position of particles in space, there are several types:

1. atomic;
2. ionic;
3. molecular;
4. metal.

In liquid and gaseous states, substances do not have a clear lattice; their molecules move chaotically, which is why they have no shape. For example, oxygen, when in a gaseous state, is a colorless, odorless gas; in a liquid state (at -194 degrees) it is a bluish solution. When the temperature drops to -219 degrees, oxygen turns into a solid state and becomes red. lattice, while it turns into a snow-like mass blue.

Interestingly, amorphous substances do not have a clear structure, which is why they do not have strict melting and boiling points. When heated, resin and plasticine gradually soften and become liquid; they do not have a clear transition phase.

Atomic crystal lattice

The nodes contain atoms, as the name suggests. These substances are very strong and durable, since a covalent bond is formed between the particles. Neighboring atoms share a pair of electrons with each other (or, more precisely, their electron clouds are layered on top of each other), and therefore they are very well connected to each other. The most obvious example is diamond, which has the greatest hardness on the Mohs scale. Interestingly, diamond, like graphite, consists of carbohydrates. Graphite is a very brittle substance (Mohs hardness 1), which is a clear example how much depends on the species.

Atomic region lattice poorly distributed in nature, it includes: quartz, boron, sand, silicon, silicon oxide (IV), germanium, rock crystal. These substances are characterized by a high melting point, strength, and these compounds are very hard and insoluble in water. Due to the very strong bond between atoms, these chemical compounds They hardly interact with others and conduct current very poorly.

Ionic crystal lattice

In this type, ions are located at each node. Accordingly, this type is characteristic of substances with ionic bonds, for example: potassium chloride, calcium sulfate, copper chloride, silver phosphate, copper hydroxide, and so on. Substances with such a particle connection scheme include;

• salt;
• metal hydroxides;
• metal oxides.

Sodium chloride has alternating positive (Na +) and negative (Cl -) ions. One chlorine ion located in a node attracts two sodium ions (due to the electromagnetic field) that are located in neighboring nodes. Thus, a cube is formed in which the particles are interconnected.

The ionic lattice is characterized by strength, refractoriness, stability, hardness and non-volatility. Some substances can conduct electricity.

Molecular crystal lattice

The nodes of this structure contain molecules that are tightly packed together. Such substances are characterized by covalent polar and nonpolar bonds. Interestingly, regardless of covalent bond, you form a very weak attraction between the particles (due to weak van der Waals forces). That is why such substances are very fragile, have low boiling and melting points, and are also volatile. These substances include: water, organic substances (sugar, naphthalene), carbon monoxide (IV), hydrogen sulfide, noble gases, two- (hydrogen, oxygen, chlorine, nitrogen, iodine), three- (ozone), four- (phosphorus ), eight-atomic (sulfur) substances, and so on.

One of distinctive features — this is that the structural and spatial model is preserved in all phases (both solid, liquid and gaseous).

Metal crystal lattice

Due to the presence of ions at the nodes, the metal lattice may appear to be similar to an ionic lattice. In fact, these are two completely different models, with different properties.

Metal is much more flexible and ductile than ionic, it is characterized by strength, high electrical and thermal conductivity, these substances melt well and conduct electric current well. This is explained by the fact that the nodes contain positively charged metal ions (cations), which can move throughout the structure, thereby ensuring the flow of electrons. The particles move chaotically around their node (they do not have enough energy to go beyond), but as soon as an electric field appears, electrons form a stream and rush from the positive to the negative region.

The metal crystal lattice is characteristic of metals, for example: lead, sodium, potassium, calcium, silver, iron, zinc, platinum and so on. Among other things, it is divided into several types of packaging: hexagonal, body-centered (least dense) and face-centered. The first package is typical for zinc, cobalt, magnesium, the second for barium, iron, sodium, the third for copper, aluminum and calcium.

Thus, depending on the grating type many properties depend, as well as the structure of the substance. Knowing the type, you can predict, for example, what the refractoriness or strength of an object will be.

It is not individual atoms or molecules that enter into chemical interactions, but substances.

Our task is to get acquainted with the structure of matter.

At low temperatures, substances are in a stable solid state.

☼ The hardest substance in nature is diamond. He is considered the king of all gems and precious stones. And its name itself means “indestructible” in Greek. Diamonds have long been looked upon as miraculous stones. It was believed that a person wearing diamonds does not know stomach diseases, is not affected by poison, retains his memory and a cheerful mood until old age, and enjoys royal favor.

☼ A diamond that has been subjected to jewelry processing - cutting, polishing - is called a diamond.

When melting as a result of thermal vibrations, the order of the particles is disrupted, they become mobile, while the nature of the chemical bond is not disrupted. Thus, there are no fundamental differences between solid and liquid states.

The liquid acquires fluidity (i.e., the ability to take the shape of a vessel).

Liquid crystals

Liquid crystals were discovered at the end of the 19th century, but have been studied in the last 20-25 years. Many display devices of modern technology, for example, some electronic watches and mini-computers, operate on liquid crystals.

In general, the words “liquid crystals” sound no less unusual than “ hot ice". However, in reality, ice can also be hot, because... at a pressure of more than 10,000 atm. water ice melts at temperatures above 200 0 C. The unusualness of the combination “liquid crystals” is that the liquid state indicates the mobility of the structure, and the crystal implies strict ordering.

If a substance consists of polyatomic molecules of an elongated or lamellar shape and having an asymmetrical structure, then when it melts, these molecules are oriented in a certain way relative to each other (their long axes are parallel). In this case, the molecules can move freely parallel to themselves, i.e. the system acquires the property of fluidity characteristic of a liquid. At the same time, the system retains an ordered structure, which determines the properties characteristic of crystals.

The high mobility of such a structure makes it possible to control it through very weak influences (thermal, electrical, etc.), i.e. purposefully change the properties of a substance, including optical ones, with very little energy consumption, which is what is used in modern technology.

Types of crystal lattices

Any chemical substance is formed by a large number of identical particles that are interconnected.

At low temperatures, when thermal movement is difficult, the particles are strictly oriented in space and form crystal lattice.

Crystal lattice – This structure with a geometrically correct arrangement of particles in space.

In the crystal lattice itself, nodes and internodal space are distinguished.

The same substance depending on the conditions (p, t,...)exists in various crystalline forms (i.e. they have different crystal lattices) - allotropic modifications that differ in properties.

For example, four modifications of carbon are known: graphite, diamond, carbyne and lonsdaleite.

☼ The fourth variety of crystalline carbon, “lonsdaleite,” is little known. It was discovered in meteorites and obtained artificially, and its structure is still being studied.

☼ Soot, coke, and charcoal were classified as amorphous carbon polymers. However, it has now become known that these are also crystalline substances.

☼ By the way, shiny black particles were found in the soot, which were called “mirror carbon.” Mirror carbon is chemically inert, heat-resistant, impervious to gases and liquids, has a smooth surface and is absolutely compatible with living tissues.

☼ The name graphite comes from the Italian “graffito” - I write, I draw. Graphite is a dark gray crystal with a weak metallic luster and has a layered lattice. Individual layers of atoms in a graphite crystal, connected to each other relatively weakly, are easily separated from each other.

TYPES OF CRYSTAL LATTICES

	ionic			metal
What is in the nodes of the crystal lattice, structural unit	ions	atoms	molecules	atoms and cations
Type of chemical bond between particles of the node	ionic		covalent: polar and non-polar	metal
Interaction forces between crystal particles	electrostatic logical	covalent	intermolecular- new	electrostatic logical
Physical properties, caused by the crystal lattice	· the attractive forces between ions are strong, · T pl. (refractory), · easily dissolves in water, · melt and solution conducts electric current, non-volatile (no odor)	· covalent bonds between atoms are large, · T pl. and T kip is very, · do not dissolve in water, · the melt does not conduct electric current	· the forces of attraction between molecules are small, · T pl. ↓, some are soluble in water, · have a volatile odor	· interaction forces are large, · T pl. , High heat and electrical conductivity
Physical state substances under normal conditions	hard	hard	hard, gaseous liquid	hard, liquid(N g)
Examples	most salts, alkalis, oxides of typical metals	C (diamond, graphite), Si, Ge, B, SiO 2, CaC 2, SiC (carborundum), BN, Fe 3 C, TaC (t pl. =3800 0 C) Red and black phosphorus. Oxides of some metals.	all gases, liquids, most non-metals: inert gases, halogens, H 2, N 2, O 2, O 3, P 4 (white), S 8. Hydrogen compounds of non-metals, oxides of non-metals: H 2 O, CO 2 "dry ice". Most organic compounds.	Metals, alloys

If the rate of crystal growth is low upon cooling, a glassy state (amorphous) is formed.

1. The relationship between the position of an element in the Periodic Table and the crystal lattice of its simple substance.

There is a close relationship between the position of an element in the periodic table and the crystal lattice of its corresponding elemental substance.

		group
				III				VII	VIII
n e r And O d								H 2
						N 2	O2	F 2
	III					P 4	S 8	Cl2
								BR 2
								I 2
Type crystal lattice		metal					atomic	molecular

The simple substances of the remaining elements have a metallic crystal lattice.

FIXING

Study the lecture material and answer the following questions in writing in your notebook:

1. What is a crystal lattice?
2. What types of crystal lattices exist?
3. Characterize each type of crystal lattice according to the plan: What is in the nodes of the crystal lattice, structural unit → Type of chemical bond between the particles of the node → Interaction forces between the particles of the crystal → Physical properties due to the crystal lattice → Aggregate state of the substance under normal conditions → Examples

Complete tasks on this topic:

1. What type of crystal lattice does the following substances commonly used in everyday life have: water, acetic acid (CH 3 COOH), sugar (C 12 H 22 O 11), potash fertilizer(KCl), river sand (SiO 2) - melting point 1710 0 C, ammonia (NH 3), table salt? Make a general conclusion: by what properties of a substance can one determine the type of its crystal lattice?
2. Using the formulas of the given substances: SiC, CS 2, NaBr, C 2 H 2 - determine the type of crystal lattice (ionic, molecular) of each compound and, based on this, describe the physical properties of each of the four substances.
   
3. Trainer No. 1. "Crystal lattices"
   
4. Trainer No. 2. "Test tasks"
   
5. Test (self-control):

1) Substances that have a molecular crystal lattice, as a rule:

a). refractory and highly soluble in water
b). fusible and volatile
V). Solid and electrically conductive
G). Thermally conductive and plastic

2) The concept of “molecule” not applicable in relation to the structural unit of a substance:

a). water

b). oxygen

V). diamond

G). ozone

3) The atomic crystal lattice is characteristic of:

a). aluminum and graphite

b). sulfur and iodine

V). silicon oxide and sodium chloride

G). diamond and boron

4) If a substance is highly soluble in water, it has high temperature melting, electrically conductive, then its crystal lattice:

A). molecular

b). atomic

V). ionic

G). metal