Chemical compounds with ionic crystal lattices are different. The structure of matter

A substance, as you know, can exist in three states of aggregation: gaseous, liquid and solid (Fig. 70). For example, oxygen, which under normal conditions is a gas, at a temperature of -194 ° C turns into a blue liquid, and at a temperature of -218.8 ° C it solidifies into a snow-like mass consisting of blue crystals.

Rice. 70.
Aggregate states of water

Solids are divided into crystalline and amorphous.

Amorphous substances do not have a clear melting point - when heated, they gradually soften and become fluid. Amorphous substances include most plastics (for example, polyethylene), wax, chocolate, plasticine, various resins and chewing gums (Fig. 71).

Rice. 71.
Amorphous substances and materials

Crystalline substances are characterized by the correct arrangement of their constituent particles at strictly defined points in space. When these points are connected by straight lines, a spatial frame is formed, called the crystal lattice. The points at which crystal particles are located are called lattice nodes.

At the nodes of an imaginary crystal lattice there can be monatomic ions, atoms, molecules. These particles oscillate. With an increase in temperature, the range of these oscillations increases, which, as a rule, leads to thermal expansion of bodies.

Depending on the type of particles located at the nodes of the crystal lattice, and the nature of the connection between them, four types of crystal lattices are distinguished: ionic, atomic, molecular and metallic (Table 6).

Table 6
The position of the elements in the Periodic system of D. I. Mendeleev and the types of crystal lattices of their simple substances

Simple substances formed by elements not listed in the table have a metal lattice.

Ionic crystal lattices are called, in the nodes of which there are ions. They are formed by substances with an ionic bond, which can be associated with both simple ions Na +, Cl -, and complex ones, OH -. Consequently, ionic crystal lattices have salts, bases (alkalis), some oxides. For example, a sodium chloride crystal is built from alternating positive Na + and negative Cl - ions, forming a cube-shaped lattice (Fig. 72). The bonds between the ions in such a crystal are very strong. Therefore, substances with an ionic lattice have a relatively high hardness and strength, they are refractory and non-volatile.

Rice. 72.
Ionic crystal lattice (sodium chloride)

Atomic lattices are called crystal lattices, in the nodes of which there are individual atoms. In such lattices, the atoms are interconnected by very strong covalent bonds.

Rice. 73.
Atomic crystal lattice (diamond)

This type of crystal lattice has a diamond (Fig. 73) - one of the allotropic modifications of carbon. Cut and polished diamonds are called brilliants. They are widely used in jewelry (Fig. 74).

Rice. 74.
Two imperial crowns with diamonds:
a - the crown of the British Empire; b - Great Imperial Crown of the Russian Empire

Substances with an atomic crystal lattice include crystalline boron, silicon and germanium, as well as complex substances, such as silica, quartz, sand, rock crystal, which include silicon oxide (IV) SiO 2 (Fig. 75).

Rice. 75.
Atomic crystal lattice (silicon (IV) oxide)

Most substances with an atomic crystal lattice have very high melting points (for example, for diamond it is over 3500 ° C, for silicon - 1415 ° C, for silica - 1728 ° C), they are strong and hard, practically insoluble.

Molecular lattices are called crystal lattices, at the nodes of which molecules are located. Chemical bonds in these molecules can be both covalent polar (hydrogen chloride HCl, water H 2 0), and covalent non-polar (nitrogen N 2, ozone 0 3). Despite the fact that the atoms within the molecules are bound by very strong covalent bonds, there are weak forces of intermolecular attraction between the molecules themselves. Therefore, substances with molecular crystal lattices have low hardness, low melting points, and are volatile.

Examples of substances with molecular crystal lattices are solid water - ice, solid carbon monoxide (IV) C) 2 - “dry ice” (Fig. 76), solid hydrogen chloride HCl and hydrogen sulfide H 2 S, solid simple substances formed by one- (noble gases: helium, neon, argon, krypton), two- (hydrogen H 2, oxygen O 2, chlorine Cl 2, nitrogen N 2, iodine 1 2), three- (ozone O 3), four- (white phosphorus P 4 ), eight-atom (sulfur S 7) molecules. Most solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).

Rice. 76.
Molecular crystal lattice (carbon dioxide)

Substances with a metallic bond have metallic crystal lattices (Fig. 77). At the nodes of such lattices there are atoms and ions (either atoms or ions, into which metal atoms easily turn, giving their outer electrons for common use). Such an internal structure of metals determines their characteristic physical properties: malleability, plasticity, electrical and thermal conductivity, metallic luster.

Rice. 77.
Metallic crystal lattice (iron)

Laboratory experiment No. 13
Acquaintance with the collection of substances with different types of crystal lattice. Making models of crystal lattices

Review the collection of samples of substances given to you. Write down their formulas, characterize the physical properties and, based on them, determine the type of crystal lattice.

Assemble a model of one of the crystal lattices.

For substances having a molecular structure, the law of composition constancy discovered by the French chemist J. L. Proust (1799-1803) is valid. This law is currently formulated as follows:

Proust's law is one of the fundamental laws of chemistry. However, for substances of a nonmolecular structure, for example, ionic, this law is not always true.

Keywords and phrases

1. Solid, liquid and gaseous states of matter.
2. Solids: amorphous and crystalline.
3. Crystal lattices: ionic, atomic, molecular and metallic.
4. Physical properties of substances with different types of crystal lattices.
5. The law of constancy of composition.

Work with computer

1. Please refer to the electronic application. Study the material of the lesson and complete the suggested tasks.
2. Search the Internet for email addresses that can serve as additional sources that reveal the content of the keywords and phrases of the paragraph. Offer the teacher your help in preparing a new lesson - make a report on the key words and phrases of the next paragraph.

Questions and tasks

1. In what state of aggregation will oxygen be at -205 ° C?
2. Remember the work of A. Belyaev "The seller of air" and characterize the properties of solid oxygen using its description given in the book.
3. What type of substance (crystalline or amorphous) are plastics? What properties of plastics underlie their industrial applications?
4. What type of diamond crystal lattice is it? List the physical properties of a diamond.
5. What type of crystal lattice is iodine? List the physical properties of iodine.
6. Why does the melting point of metals vary over a very wide range? To prepare an answer to this question, use additional literature.
7. Why does a product made of silicon break into pieces on impact, while a product made of lead only flattens out? In which of these cases does the destruction of a chemical bond occur, and in which does not? Why?

Most solids have crystalline structure that is characterized strictly defined arrangement of particles. If you connect the particles with conditional lines, you get a spatial frame called crystal lattice. The points where the crystal particles are located are called lattice nodes. The nodes of an imaginary lattice can contain atoms, ions or molecules.

Depending on the nature of the particles located at the nodes, and the nature of the connection between them, four types of crystal lattices are distinguished: ionic, metallic, atomic and molecular.

Ionic called lattices, in the nodes of which there are ions.

They are formed by substances with ionic bonds. At the nodes of such a lattice, positive and negative ions are located, interconnected by electrostatic interaction.

Ionic crystal lattices have salts, alkalis, active metal oxides. Ions can be simple or complex. For example, at the sites of the crystal lattice of sodium chloride there are simple sodium ions Na and chlorine Cl - , and at the lattice sites of potassium sulfate, simple potassium ions K and complex sulfate ions S O 4 2 - alternate.

The bonds between ions in such crystals are strong. Therefore, ionic substances are solid, refractory, non-volatile. Such substances are good dissolve in water.

The crystal lattice of sodium chloride

Sodium chloride crystal

metal called lattices, which consist of positive ions and metal atoms and free electrons.

They are formed by substances with a metallic bond. At the nodes of the metal lattice there are atoms and ions (either atoms or ions, into which atoms easily turn, giving their outer electrons for common use).

Such crystal lattices are characteristic of simple substances of metals and alloys.

The melting points of metals can be different (from \ (-37 \) ° С for mercury to two to three thousand degrees). But all metals have a characteristic metallic luster, malleability , ductility , good conductor of electricity and warmly.

metal crystal lattice

Hardware

Atomic crystal lattices are called, in the nodes of which there are individual atoms connected by covalent bonds.

This type of lattice has a diamond - one of the allotropic modifications of carbon. Substances with an atomic crystal lattice include graphite, silicon, boron and germanium, as well as complex substances, for example, carborundum SiC and silica, quartz, rock crystal, sand, which include silicon oxide (\ (IV \)) Si O 2.

Such substances are characterized high strength and hardness. Thus, diamond is the hardest natural substance. Substances with an atomic crystal lattice have a very high melting points and boiling. For example, the melting point of silica is \(1728 \) ° C, while for graphite it is higher - \ (4000 \) ° C. Atomic crystals are practically insoluble.

Diamond crystal lattice

Diamond

Molecular called lattices, at the nodes of which there are molecules bound by a weak intermolecular interaction.

Despite the fact that inside the molecules the atoms are connected by very strong covalent bonds, weak forces of intermolecular attraction act between the molecules themselves. Therefore, molecular crystals have little strength and hardness low melting points and boiling. Many molecular substances are liquids and gases at room temperature. Such substances are volatile. For example, crystalline iodine and solid carbon monoxide (\ (IV \)) (“dry ice”) evaporate without turning into a liquid state. Some molecular substances are smell .

Simple substances in a solid state of aggregation have this type of lattice: noble gases with monatomic molecules (He, Ne, Ar, Kr, Xe, Rn ), as well as non-metals with two- and polyatomic molecules (H 2, O 2, N 2, Cl 2, I 2, O 3, P 4, S 8).

The molecular crystal lattice has also substances with covalent polar bonds: water - ice, solid ammonia, acids, non-metal oxides. Majority organic compounds are also molecular crystals (naphthalene, sugar, glucose).

As we know, all material substances can exist 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 matter is therefore solid, because it has a special crystalline structure, the particles of which are in a certain and well-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 interconnected 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, of ions, as a result of which an electromagnetic field is formed that determines the properties of substances that have an ionic crystal lattice. And this is refractoriness, hardness, density and the ability to conduct electric current. Salt can be a typical example of an ionic crystal lattice.

Atomic crystal lattice

Substances with an atomic crystal lattice, as a rule, have strong nodes in their nodes, consisting of atoms proper. A covalent bond occurs when two identical atoms fraternally share electrons with each other, 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 similar bonds can boast of their hardness, high melting point. The atomic crystal lattice has such chemical elements as diamond, silicon, germanium, boron.

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 one, although outwardly they are very similar. Its distinctive feature is the presence of positively charged cations (metal ions) at the lattice sites. Between the nodes live electrons involved in the creation of an electric field, these electrons are also called electric gas. The presence of such a structure of a metal crystal lattice explains its properties: mechanical strength, thermal and electrical conductivity, fusibility.

Crystal lattices, video

And finally, a detailed video explanation of the properties of crystal lattices.

Page 1

Molecular crystal lattices and their corresponding molecular bonds are formed mainly in the crystals of those substances in whose molecules the bonds are covalent. When heated, the bonds between molecules are easily destroyed, so substances with molecular lattices have low melting points.

Molecular crystal lattices are formed from polar molecules, between which interaction forces arise, the so-called van der Waals forces, which are electrical in nature. In the molecular lattice, they carry out a rather weak bond. Ice, natural sulfur and many organic compounds have a molecular crystal lattice.

The molecular crystal lattice of iodine is shown in fig. 3.17. Most crystalline organic compounds have a molecular lattice.

The nodes of the molecular crystal lattice are formed by molecules. Molecular lattice have, for example, crystals of hydrogen, oxygen, nitrogen, noble gases, carbon dioxide, organic substances.

The presence of the molecular crystal lattice of the solid phase is the reason for the insignificant adsorption of ions from the mother liquor, and, consequently, the much higher purity of the precipitates compared to the precipitates, which are characterized by an ionic crystal. Since the precipitation in this case occurs in the optimal range of acidity, which is different for the ions precipitated by this reagent, it depends on the value of the corresponding stability constants of the complexes. This fact makes it possible, by adjusting the acidity of the solution, to achieve selective and sometimes even specific precipitation of certain ions. Similar results can often be obtained by suitably modifying the donor groups in the organic reagents, taking into account the characteristics of the complexing cations that precipitate.

In molecular crystal lattices, local anisotropy of bonds is observed, namely, intramolecular forces are very large compared to intermolecular ones.

In molecular crystal lattices, molecules are located at the lattice sites. Most substances with a covalent bond form crystals of this type. Molecular lattices form solid hydrogen, chlorine, carbon dioxide and other substances that are gaseous at ordinary temperatures. Crystals of most organic substances are also of this type. Thus, a lot of substances with a molecular crystal lattice are known.

In molecular crystal lattices, their constituent molecules are bound together by relatively weak van der Waals forces, while the atoms within the molecule are bound by a much stronger covalent bond. Therefore, in such lattices, the molecules retain their individuality and occupy one site of the crystal lattice. Substitution here is possible if the molecules are similar in shape and size. Since the forces that bind the molecules are relatively weak, the limits of substitution here are much wider. As Nikitin showed, atoms of noble gases can isomorphically replace the molecules of CO2, SO2, CH3COCH3 and others in the lattices of these substances. The similarity of the chemical formula is not necessary here.

In molecular crystal lattices, molecules are located at the lattice sites. Most substances with a covalent bond form crystals of this type. Molecular lattices form solid hydrogen, chlorine, carbon dioxide and other substances that are gaseous at ordinary temperatures. Crystals of most organic substances are also of this type. Thus, a lot of substances with a molecular crystal lattice are known. Molecules located at the lattice sites are bound to each other by intermolecular forces (the nature of these forces was discussed above; see p. Since intermolecular forces are much weaker than chemical bonding forces, molecular crystals of low melting point are characterized by significant volatility, their hardness is low. Particularly low the melting and boiling points of those substances whose molecules are non-polar.For example, paraffin crystals are very soft, although the C-C covalent bonds in the hydrocarbon molecules that make up these crystals are as strong as the bonds in diamond. gases, should also be attributed to molecular gases, consisting of monatomic molecules, since valence forces do not play a role in the formation of these crystals, and the bonds between particles here have the same character as in other molecular crystals; this causes a relatively large value of interatomic distances in these crystals.

At the nodes of molecular crystal lattices there are molecules that are connected to each other by weak intermolecular forces. Such crystals form substances with a covalent bond in molecules. A lot of substances with a molecular crystal lattice are known. Molecular lattices have solid hydrogen, chlorine, carbon dioxide and other substances that are gaseous at ordinary temperature. Crystals of most organic substances are also of this type.