The bonds between ions in a crystal are very strong and stable; therefore, substances with an ionic lattice have high hardness and strength, are refractory and non-volatile.

Substances with an ionic crystal lattice have the following properties:

1. Relatively high hardness and strength;

2. Fragility;

3. Heat resistance;

4. Refractoriness;

5. Non-volatility.

Examples: salts - sodium chloride, potassium carbonate, bases - calcium hydroxide, sodium hydroxide.

4. Mechanism of covalent bond formation (exchange and donor-acceptor).

Each atom seeks to complete its outer electronic level in order to reduce potential energy. Therefore, the nucleus of one atom is attracted to itself by the electron density of another atom and vice versa, the superposition of the electron clouds of two neighboring atoms occurs.

Demonstration of the application and the scheme for the formation of a covalent non-polar chemical bond in a hydrogen molecule. (Students write and sketch diagrams).

Conclusion: The bond between atoms in a hydrogen molecule is carried out due to a common electron pair. This bond is called covalent.

What kind of bond is called covalent non-polar? (Tutorial page 33).

Compilation of electronic formulas of molecules of simple substances of non-metals:

CI CI is the electronic formula of the chlorine molecule,

CI - CI is the structural formula of the chlorine molecule.

N N is the electronic formula of the nitrogen molecule,

N ≡ N is the structural formula of the nitrogen molecule.

Electronegativity. Covalent polar and non-polar bonds. The multiplicity of the covalent bond.

But molecules can also form different atoms of non-metals, and in this case, the total electron pair will shift to a more electronegative chemical element.

Explore the tutorial on page 34

Conclusion: Metals have a lower electronegativity value than non-metals. And between them it is very different.

Demonstration of the scheme for the formation of a polar covalent bond in a molecule of hydrogen chloride.

The total electron pair is biased towards chlorine, as it is more electronegative. So this is a covalent bond. It is formed by atoms, the electronegativities of which are slightly different, therefore it is a covalent polar bond.

Compilation of electronic formulas of molecules of hydrogen iodide and water:

H J is the electronic formula of the hydrogen iodide molecule,

H → J is the structural formula of the hydrogen iodide molecule.

HO is the electronic formula of a water molecule,

H → O is the structural formula of a water molecule.

Independent work with the textbook: write out the definition of electronegativity.

Molecular and atomic crystal lattices. Properties of substances with molecular and atomic crystal lattices

Independent work with the textbook.

Questions for self-control

Atom of which chemical element has a nucleus charge +11

- Write down the diagram of the electronic structure of the sodium atom

- Is the outer layer finished?

- How to achieve completion of the filling of the electronic layer?

- Make a diagram of the electron return

- Compare the structure of the atom and ion of sodium

Compare the structure of the atom and ion of an inert gas neon.

Determine the atom, which element with the number of protons 17.

- Write down the diagram of the electronic structure of the atom.

- Is the layer complete? How to achieve this.

- Draw up a diagram of the completion of the electronic chlorine layer.

Group assignment:

Group 1-3: Make up the electronic and structural formulas of molecules of substances and indicate the type of bond Br 2; NH 3.

4-6 groups: Make up the electronic and structural formulas of molecules of substances and indicate the type of bond F 2; HBr.

Two students work at an additional board with the same task for a sample for self-examination.

Oral survey.

1. Give a definition of the concept of "electronegativity".

2. What determines the electronegativity of an atom?

3. How does the electronegativity of atoms of elements change in periods?

4. How does the electronegativity of atoms of elements in the main subgroups change?

5. Compare the electronegativity of metal and non-metal atoms. Are the termination methods of the outer electron layer different for metal and non-metal atoms? What are the reasons for this?

7. What chemical elements are capable of giving electrons, accepting electrons?

What happens between atoms when you give and receive electrons?

What is the name of the particles formed from an atom as a result of the recoil or attachment of electrons?

8. What happens when metal and non-metal atoms meet?

9. How is ionic bond formed?

10. The chemical bond formed by the formation of common electron pairs is called ...

11. A covalent bond happens ... and ...

12. What are the similarities between covalent polar and covalent non-polar bonds? What does the polarity of the connection depend on?

13. What is the difference between covalent polar and covalent non-polar bonds?

LESSON PLAN number 8

Discipline: Chemistry.

Topic:Metallic bond. Aggregate states of substances and hydrogen bond .

The purpose of the lesson: Form the concept of chemical bonds using the example of a metal bond. Achieve an understanding of the mechanism of communication formation.

Planned results

Subject: the formation of a person's outlook and functional literacy for solving practical problems; the ability to process, explain the results; readiness and ability to apply cognitive methods in solving practical problems;

Metasubject: use of various sources to obtain chemical information, the ability to assess its reliability to achieve good results in the professional field;

Personal: the ability to use the achievements of modern chemical science and chemical technologies to enhance their own intellectual development in the chosen professional activity;

Time rate:2 hours

Activity type:Lecture.

Lesson plan:

1. Metallic bond. Metallic crystal lattice and metallic chemical bond.

2. Physical properties of metals.

3. Aggregate states of substances. The transition of a substance from one state of aggregation to another.

4. Hydrogen bond

Equipment: Periodic table of chemical elements, crystal lattice, handout.

Literature:

1. Chemistry grade 11: textbook. for general education. organizations G.E. Rudzitis, F.G. Feldman. - M.: Education, 2014.-208 p .: ill ..

2. Chemistry for professions and specialties of a technical profile: a textbook for students. institutions of environments. prof. Education / O.S. Gabrielyan, I.G. Ostroumov. - 5 - ed., Erased. - M .: Publishing Center "Academy", 2017. - 272p., With color. silt

Teacher: Tubaltseva Yu.N.

The structure of matter is determined not only by the mutual arrangement of atoms in chemical particles, but also by the arrangement of these chemical particles in space. The placement of atoms, molecules and ions in crystals is most ordered, where chemical particles are arranged in a certain order, forming in space crystal lattice.

Depending on which particles the crystal lattice is built from and what is the nature of the chemical bond between them, different types of crystal lattices:

· Atomic

· Molecular

· Metal

· Ionic

Ionic crystal lattices are formed by ions - cations and anions. In knotsionic lattice, IONS are located - cations and anions, between which there is ELECTROSTATIC attraction.

This is a fairly durable type of grille.

‼ Characteristics of substances with an ionic crystal lattice:

· high melting points (refractoriness)–Ionic compounds are always solid under normal conditions;

· solubility in water most ionic compounds;

· Solutions and melts conduct electric current.

What substances have an ION lattice?

‼ The ionic lattice is characteristic of substances with an IONIC TYPE of bonds (salts, bases, metal oxides, other compounds containing metal and non-metal).

Atomic crystal lattices are composed of individual atoms connected strong covalent bonds.

Graphite crystal

‼ Characteristics of substances with an atomic crystal lattice:

Atomic crystals are very strong and solid

· Poorly conduct heat and electricity.

· Melt at high temperatures.

· insoluble in any solvents.

· Low reactivity.

What substances have an ATOMIC lattice?

‼ Substances with atomic crystal lattice:

1) simple substances - boron, silicon, carbon (diamond and graphite).

2) silicon oxide (silica), silicon carbide (carborundum), as well as boron carbide and nitride.

Molecular crystal lattices are composed of individual molecules, within which atoms are linked by covalent bonds. Between molecules weaker intermolecular (van der Waals) forces act. This is a very weak interaction.

Iodine molecule.

‼ Characteristics of substances with a molecular crystal lattice:

Substances are gaseous, liquid and solid

· low melting points

Low lattice strength

High volatility of substances

Do not have electrical conductivity

· Their solutions and melts also do not conduct electric current.

What substances have a MOLECULAR Lattice?

‼ Substances with molecular lattice:

· simple diatomic substances-non-metals

· compounds of non-metals(except oxides and carbides of boron and silicon)

· all organic compounds, except salts.

The metal crystal lattice is typical for simple metal substances. It takes place metal bond between atoms. At the nodes of the lattice - metal cations; socialized electrons ("electron gas") move between them, which hold metal cations, attracting them to themselves. The bond in such crystals is delocalized and extends to the entire crystal.

In metal crystals, the atomic nuclei are arranged in such a way that their packing is as dense as possible.

‼ Characteristics of substances with a metal crystal lattice:

· metallic luster and opacity

· malleability and ductility

Crystalline substances

Solid crystals - three-dimensional formations characterized by the strict repeatability of the same structural element ( unit cell) in all directions. A 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 primarily due to their strictly regular internal structure. If, instead of atoms, ions or molecules in a crystal, we depict the points as the centers of gravity of these particles, then we get a three-dimensional regular distribution of such points, called the crystal lattice. The points themselves are called knots crystal lattice.

Types of crystal lattices

Different types of crystals are distinguished depending on what particles are used to build the crystal lattice and what is the nature of the chemical bond between them.

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

Ionic crystals can be composed 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 NO3? , 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 attaching new cations and anions.

Most ionic compounds crystallize according to one of the structural types, which differ from each other in the value of the coordination number, that is, in the number of neighbors around a given ion (4, 6, or 8). For ionic compounds with an equal number of 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 half the number of 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), cristobalite (coordination numbers 4 and 2) are realized.

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

Ionic crystals have high melting points. In a 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 an electric current.

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

Atomic crystals are made up of individual atoms linked by covalent bonds. Of the simple substances, only boron and elements of the IVA group have such crystal lattices. Often, the 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, poorly conducts heat and electricity. Substances with atomic crystal lattices melt at high temperatures. They are practically insoluble in any kind of solvent. They are characterized by low reactivity.

Molecular crystals are built from individual molecules, inside which atoms are connected by covalent bonds. Weaker intermolecular forces act between molecules. They are easily destroyed, therefore 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 negatively charged electrons of one molecule with positively charged nuclei of neighboring molecules. The strength of intermolecular interaction is influenced by many factors. The most important among them is the presence of polar bonds, that is, the displacement of the electron density from one atom to another. In addition, intermolecular interactions are more pronounced between molecules with a large number of electrons.

Most non-metals 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 practically all organic solids form molecular crystals.

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

The classification of crystal lattices corresponds to limiting cases. Most crystals of inorganic substances belong to intermediate types - covalent-ionic, molecular-covalent, etc. For example, in a crystal graphite inside each layer, bonds are covalent-metallic, and between layers - 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. Micherlich in 1819. The law of isomorphism would have been formulated by E. Micherlich in 1821 as follows:" The same number of atoms, connected in the same way, give the same crystal forms; the crystalline form does not depend on the chemical nature of atoms, but is determined only by their number and relative position. "

While working in the chemical laboratory of the University of Berlin, Micherlich drew attention to the complete similarity of the crystals of lead, barium and strontium sulfates and the similarity of the crystal forms of many other substances. His observations attracted the attention of the famous Swedish chemist J.-J. Berzelius, who suggested to Micherlich to 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." Micherlich's discovery very soon attracted the attention of mineralogists, who began research on the problem of isomorphic substitution of elements in minerals.

With joint crystallization of substances prone to isomorphism ( isomorphic substances), mixed crystals (isomorphic mixtures) are formed. This is possible only if the particles replacing each other differ little in size (no more than 15%). In addition, isomorphic substances should have a similar spatial arrangement of atoms or ions and, therefore, crystals similar in external form. 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 trace and trace elements, their distribution in rocks and ores, where they are contained in the form of isomorphic impurities.

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

Many substances can form crystalline forms with 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 of CaCO 3.

Polymorphism of simple substances is usually called allotropy, at the same time, 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 carbon modifications (diamond, lonsdaleite, graphite, carbines, and fullerenes), which differ sharply in properties. The most stable form of carbon existence is graphite; however, other modifications of it under normal conditions can persist indefinitely. At high temperatures, they transform 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 accomplish. Not only a high temperature (1200-1600 o С) is required, but also a gigantic 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 a different packing of molecules in a crystal or in a change in the shape of molecules, and in ionic crystals, in a different mutual arrangement of cations and anions. Some simple and complex substances have more than two polymorphic modifications. For example, silicon dioxide has ten modifications, calcium fluoride six, ammonium nitrate four. Polymorphic modifications are usually denoted by the Greek letters b, c, d, e, e, ... starting with modifications that are stable at low temperatures.

During crystallization from steam, solution or melt of a substance having several polymorphic modifications, a modification is first formed that is less stable under these conditions, which then turns into a more stable one. For example, when phosphorus vapor condenses, white phosphorus is formed, which under normal conditions slowly, and when heated, quickly turns into red phosphorus. When lead hydroxide is dehydrated, at the beginning (about 70 ° C), yellow β-PbO, less stable at low temperatures, is formed, at about 100 ° C it turns into red β-PbO, and at 540 ° C - again into β-PbO.

The transition from one polymorphic modification to another is called polymorphic transformations. These transitions occur with a change in temperature or pressure and are accompanied by an abrupt change in properties.

The process of transition from one modification to another can be reversible or irreversible. So, when heating a white soft graphite-like substance of composition BN (boron nitride) 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 \u200b\u200bcorresponding to normal conditions, borazon retains its structure. An example of a reversible transition is the mutual transformations of two sulfur modifications (rhombic and monoclinic) at 95 o С.

Polymorphic transformations can take place without significant structural changes. Sometimes there is no change in the crystal structure at all, for example, during the transition from 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 a heat treatment, which consists in a combination of thermal and chemical action in order to change the composition, structure and properties of the surface layer of steel.

Chemical heat treatment is one of the most common types of materials processing in order to make them operational. The most widely used methods of saturation of the surface layer of steel with carbon and nitrogen, both separately and jointly. These are the processes of cementation (carburization) of the surface, nitriding - saturation of the steel surface with nitrogen, nitrocarburizing and cyanidation - the combined introduction of carbon and nitrogen into the surface layers of steel. The saturation of the surface layers of steel with other elements (chromium - diffusion chromium plating, boron - boriding, silicon - siliconizing and aluminum - aluminizing) are used much less often. The process of diffusion saturation of the surface of a part with zinc is called zinc plating, and titanium is called titanization.

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

1. Formation of active atoms in a saturating medium near the surface or directly on the metal surface. 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 of steel.

2. Adsorption (sorption) of the formed active atoms by the saturation surface. Adsorption is a complex process that occurs at the saturation surface in an unsteady manner. Distinguish between physical (reversible) adsorption and chemical adsorption (chemisorption). In chemical-thermal treatment, these types of adsorption are superimposed on each other. Physical adsorption leads to the adhesion of the 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 the 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 - the movement of adsorbed atoms in the lattice of the metal being processed. The diffusion process is possible only if the diffusing element is soluble in the material being processed and the temperature is high enough to provide the energy required for the process. The thickness of the diffusion layer, and hence the thickness of the hardened layer of the product surface, is the most important characteristic of chemical thermal treatment. The layer thickness 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 saturable element between the surface of the product and in the depth of the saturable layer.

The cutting tool works 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. the ability to maintain the cutting properties of the edge for a long time under friction conditions.

The higher the hardness of the materials to be cut, the thicker the chips and the higher the cutting speed, the greater the energy expended in the cutting process. Mechanical energy is converted into heat. The released heat heats the cutter, workpiece, 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. According to 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 cutting, carbon is released from the hardening martensite and coagulation of cementite-type carbides begins. This leads to a 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-alloyed steels, for example 9Kh5VF, retain their 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, therefore they are used for lighter operating conditions at low cutting speeds. High-speed steels with higher heat resistance and hardenability are used for more severe working conditions. Even higher cutting speeds are possible with cemented carbides and ceramics. Of the existing materials, boron nitride - elbor has the highest heat resistance, Elbor allows processing materials of high hardness, for example, hardened steel, at high speeds.

A substance can exist in three states of aggregation: gaseous, liquid, solid. For example, oxygen is a gas, but at a temperature of -194 ° C it turns into a blue liquid, and at a temperature of -218.8 ° C it solidifies into a snow-like mass, consisting of blue crystals.

Solids divided into crystalline and amorphous. Amorphous substances do not have a clear melting point, when heated, they soften and turn into a fluid state. Amorphous substances include plastics, wax, chocolate, plasticine, chewing gum.

Crystalline substances consist of particles that have a clear location at certain points in space. If you combine these particles, you get a kind of framework, which is called crystal lattice... And the points where the particles are - lattice nodes... The nodes of the crystal lattice can contain ions, atoms, molecules. These particles oscillate. With increasing temperature, the range of these oscillations increases, which leads to thermal expansion of bodies.

Crystal cell

Depending on the type of particles in the crystal lattice and the nature of the bond between them, distinguish between ionic, atomic, molecular and metallic crystal lattices.

Ionic crystal lattices

Ionic, crystal lattices are called, in which nodes are ions... Them form substances with an ionic type of bond... it salts, bases, some oxides... For instance, sodium chloride crystal, is built from alternating ions Na + and Cl -. They form a cube-shaped lattice. The bonds in this crystal are very strong, therefore, substances with an ionic type of bond have high hardness and strength, they are non-volatile and refractory.

Atomic crystal lattices

Crystal lattices are called atomic, in the nodes of which there are individual atoms... These atoms are very strong connected to each other. covalent bonds... The atomic crystal lattice has diamond... A cut and polished diamond is called diamond... It is widely used in jewelry.

In addition to diamond, such simple substances also have an atomic crystal lattice as boron, silicon, germanium, and complex: silica, quartz, sand, rock crystal, which include SiO 2. Substances with an atomic crystal lattice have high melting points, they are strong and hard, practically insoluble.

Molecular crystal lattices

Molecular crystal lattice is a crystal lattice, in the nodes of which there are molecules... The bonds in substances with a molecular crystal lattice can be covalent polar, as in HCl, H 2 O molecules, and covalent non-polar, as in O 2, O 3, N 2, H 2 molecules, etc. The atoms inside the molecule are tightly bound, but the bonds between the molecules themselves are fragile. Therefore, substances with a molecular crystal lattice have low hardness, low melting and boiling points, volatile... Substances with a molecular crystal lattice include: ice (water in a solid state of aggregation), which already at temperatures above 0 0 С becomes a liquid state, its crystal structure is destroyed; solid carbon monoxide (IV) - "dry ice", which sublimes with increasing temperature, i.e. turns into gas solid hydrogen chloride and hydrogen sulfide, solid simple substances.Such as, monatomic noble gases, diatomic molecules (O 2, N 2, H 2, Cl 2, I 2), triatomic (O 3), tetraatomic, like P 4, octatomic molecules like S 8. Most organic substances have a molecular crystal lattice: glucose, sugar, naphthalene, alcohol, citric acid.

Metal crystal lattices

The metal crystal lattice has substances with a metallic bond... The nodes of this crystal lattice are metal ions and free electrons... Therefore, substances with this type of bond have malleability, ductility, have a metallic luster, electrically and thermally.

For substances of molecular structure, it is true the law of the French chemist J.L. Proust - the law of constancy of composition: molecular chemical compounds, regardless of the method of their preparation, have a constant composition and properties. Proust's law - the basic of the laws of chemistry, but it is unfair for substances of non-molecular structure.

As we know, all material substances can be in three basic states: liquid, solid, and gaseous. True, there is also a state of plasma, which scientists consider no less than the fourth state of matter, but our article is not about plasma. The solid state of a substance is therefore solid, since it has a special crystalline structure, the particles of which are in a certain and clearly defined order, thus creating a crystal lattice. The structure of the crystal lattice consists of repeating identical elementary cells: atoms, molecules, ions, other elementary particles, connected by various nodes.

Types of crystal lattices

Depending on the particles of the crystal lattice, there are fourteen types of it, we will give the most popular of them:

• Ionic crystal lattice.
• Atomic crystal lattice.
• Molecular crystal lattice.
• crystal cell.

Ionic crystal lattice

The main feature of the structure of the crystal lattice of ions is the opposite electric charges, in fact, ions, as a result of which an electromagnetic field is formed, which determines the properties of substances with an ionic crystal lattice. And this is refractoriness, hardness, density and the ability to conduct electric current. Table salt is a typical example of an ionic crystal lattice.

Atomic crystal lattice

Substances with an atomic crystal lattice, as a rule, have strong in their nodes, which consist of atoms proper. A covalent bond occurs when two identical atoms share electrons with one another, thus forming a common pair of electrons for neighboring atoms. Because of this, covalent bonds strongly and evenly bind atoms in a strict order - perhaps this is the most characteristic feature of the structure of the atomic crystal lattice. Chemical elements with such bonds can boast of their hardness and high melting point. Such chemical elements as diamond, silicon, germanium, boron have an atomic crystal lattice.

Molecular crystal lattice

The molecular type of the crystal lattice is characterized by the presence of stable and close-packed molecules. They are located at the nodes of the crystal lattice. In these nodes, they are held by such van der Waals forces, which are ten times weaker than the forces of ionic interaction. A striking example of a molecular crystal lattice is ice - a solid substance, which, however, has the property of turning into a liquid - the bonds between the molecules of the crystal lattice are very weak.

Metal crystal lattice

The type of bond of the metal crystal lattice is more flexible and plastic than the ionic, although outwardly they are very similar. Its distinctive feature is the presence of positively charged cations (metal ions) in the lattice sites. Electrons that participate in the creation of an electric field live between the nodes, these electrons are also called electric gas. The presence of such a structure of a metal crystal lattice explains its properties: mechanical strength, heat and electrical conductivity, fusibility.