n-butane

isobutane cyclo-pentane methyl c-butane

Different positions of functional groups

OH [propanol-1] OH [propanol-2]

Different kind of functional groups (metamerism)

isomers

acid]aminoethanoic acid]

See also an example from Table. 2.

B) The difference in the electronic structure:

Different types and positions of multiple bonds

(isomers

[butadiene-1,3] [butyn-1] [butyn-2]

Ordinary structural formulas reflect only these two (A and B) aspects of the structure of molecules.

C) SPATIAL ISOMERIA (or stereoisomerism):

Such isomers have the same bond order between atoms, but differ in the spatial arrangement of their constituent atoms or groups of atoms. Special techniques are used to show the spatial structure.

These include:

(5) Cis-trans-isomerism- different arrangement of atoms relative to the double bond (a) or the ring plane (b):

Example (a) - stereoisomers of butene-2:

[cis-Butene-2] [trans-Butene-2]

Example (b) - stereoisomers:

cis form trans form

(6) Optical (mirror) isomerism

This phenomenon is due to the presence of asymmetric carbon atoms in the molecules; discussed in the sections "Hydroxyacids" and "Carbohydrates".

(7) conformational isomerism

Most substances are characterized by the ability, depending on the conditions, to be in one of three states of aggregation: solid, liquid or gaseous.

For example, water at normal pressure in the temperature range of 0-100 o C is a liquid, at temperatures above 100 o C it can only exist in a gaseous state, and at temperatures below 0 o C it is a solid.
Substances in the solid state distinguish between amorphous and crystalline.

Characteristic features amorphous substances is the lack of a clear melting point: their fluidity gradually increases with increasing temperature. Amorphous substances include compounds such as wax, paraffin, most plastics, glass, etc.

Nevertheless, crystalline substances have a specific melting point, i.e. a substance with a crystalline structure passes from a solid state to a liquid not gradually, but abruptly, when a specific temperature is reached. Examples of crystalline substances include table salt, sugar, ice.

Difference in physical properties ax amorphous and crystalline solids is primarily due to the structural features of such substances. What is the difference between a substance in an amorphous and crystalline state, the easiest way to understand is from the following illustration:

As you can see, in an amorphous substance, unlike a crystalline one, there is no order in the arrangement of particles. If, in a crystalline substance, one mentally connects two atoms close to each other with a straight line, then one can find that the same particles will lie on this line at strictly defined intervals:

Thus, in the case of crystalline substances, one can speak of such a concept as a crystal lattice.

crystal lattice called a spatial frame connecting the points of space in which there are particles that form a crystal.

The points in space where the particles that form the crystal are located are called lattice nodes .

Depending on which particles are in the nodes of the crystal lattice, there are: molecular, atomic, ionic And metal crystal lattice .

in knots molecular crystal lattice

there are molecules within which the atoms are bound by strong covalent bonds, but the molecules themselves are held near each other by weak intermolecular forces. Due to such weak intermolecular interactions, crystals with a molecular lattice are fragile. Such substances differ from substances with other types of structure by significantly lower melting and boiling points, do not conduct electricity, may or may not dissolve in various solvents. Solutions of such compounds may or may not conduct electricity, depending on the class of the compound. Compounds with a molecular crystal lattice include many simple substances - non-metals (hardened H 2, O 2, Cl 2, rhombic sulfur S 8, white phosphorus P 4), as well as many complex substances - hydrogen compounds non-metals, acids, non-metal oxides, most organic matter. It should be noted that if the substance is in a gaseous or liquid state, it is inappropriate to talk about the molecular crystal lattice: it is more correct to use the term - the molecular type of structure.

in knots atomic crystal lattice

there are atoms. In this case, all nodes of such a crystal lattice are "crosslinked" to each other by means of strong covalent bonds into a single crystal. In fact, such a crystal is one giant molecule. Due to structural features, all substances with an atomic crystal lattice are solid, have high melting points, are chemically inactive, insoluble in either water or organic solvents, and their melts do not conduct electric current. It should be remembered that substances with an atomic type of structure from simple substances include boron B, carbon C (diamond and graphite), silicon Si, from complex substances - silicon dioxide SiO 2 (quartz), silicon carbide SiC, boron nitride BN.

For substances with ionic crystal lattice

at the lattice sites are ions that are connected to each other through ionic bonds.
Since ionic bonds are strong enough, substances with an ionic lattice have a relatively high hardness and refractoriness. Most often, they are soluble in water, and their solutions, like melts, conduct electricity.
Substances with an ionic type of crystal lattice include metal and ammonium salts (NH 4 +), bases, metal oxides. A true sign of the ionic structure of a substance is the presence in its composition of both atoms typical metal and non-metal.

observed in crystals of free metals, for example, sodium Na, iron Fe, magnesium Mg, etc. In the case of a metal crystal lattice, cations and metal atoms are located at its nodes, between which electrons move. In this case, moving electrons periodically attach to cations, thus neutralizing their charge, and individual neutral metal atoms instead “release” some of their electrons, turning, in turn, into cations. In fact, "free" electrons do not belong to individual atoms, but to the entire crystal.

Such structural features lead to the fact that metals conduct heat and electric current well, often have high ductility (ductility).
The scatter in the values ​​of the melting temperatures of metals is very large. So, for example, the melting point of mercury is approximately minus 39 ° C (liquid under normal conditions), and tungsten - 3422 ° C. It should be noted that under normal conditions, all metals except mercury are solids.

Themes 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 intensive 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 mutual arrangement particles in space relative to each other!

This article considers properties 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; on geometric shape 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. from a large number 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 temperature melting):

— 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 a large number 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 while not being destroyed.

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.

Summary table on the structures of simple substances formed 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: