As we already know, a substance can exist in three states of aggregation: gaseous, hard And liquid. Oxygen, which under normal conditions is in a gaseous state, at a temperature of -194 ° C is transformed into a bluish liquid, and at a temperature of -218.8 ° C it turns into a snow-like mass with blue crystals.

The temperature range for the existence of a substance in the solid state is determined by the boiling and melting points. Solids are crystalline And amorphous.

U amorphous substances there is no fixed melting point - when heated, they gradually soften and turn into a fluid state. In this state, for example, various resins and plasticine are found.

Crystalline substances They are distinguished by the regular arrangement of the particles of which they consist: atoms, molecules and ions, at strictly defined points in space. When these points are connected by straight lines, a spatial framework is created, it is called a crystal lattice. The points at which crystal particles are located are called lattice nodes.

The nodes of the lattice we imagine can contain ions, atoms and molecules. These particles perform oscillatory movements. When the temperature increases, the range of these oscillations also increases, which 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 metal.

Ionic These are called crystal lattices in which ions are located at the nodes. They are formed by substances with ionic bonds, which can bind both simple ions Na+, Cl-, and complex SO24-, OH-. Thus, ionic crystal lattices have salts, some oxides and hydroxyls of metals, i.e. those substances in which an ionic chemical bond exists. Consider a sodium chloride crystal; it consists of positively alternating Na+ and negative CL- ions, together they form a cube-shaped lattice. The bonds between ions in such a crystal are extremely stable. Because of this, substances with an ionic lattice have relatively high strength and hardness; they are refractory and nonvolatile.

Atomic Crystal lattices are those crystal lattices whose nodes contain individual atoms. In such lattices, atoms are connected to each other by very strong covalent bonds. For example, diamond is one of the allotropic modifications of carbon.

Substances with an atomic crystal lattice are not very common in nature. These include crystalline boron, silicon and germanium, as well as complex substances, for example those containing silicon (IV) oxide - SiO 2: silica, quartz, sand, rock crystal.

The vast majority of substances with an atomic crystal lattice have very high temperatures melting (for diamond it exceeds 3500° C), such substances are strong and hard, practically insoluble.

Molecular These are called crystal lattices in which molecules are located at the nodes. Chemical bonds in these molecules can also be polar (HCl, H 2 0) or non-polar (N 2, O 3). And although the atoms inside the molecules are connected by very strong covalent bonds, weak forces of intermolecular attraction act between the molecules themselves. That is why substances with molecular crystal lattices are characterized by low hardness, low melting point, and volatility.

Examples of such substances include solid water - ice, solid carbon monoxide (IV) - “dry ice”, solid hydrogen chloride and hydrogen sulfide, solid simple substances formed by one - (noble gases), two - (H 2, O 2, CL 2 , N 2 , I 2), three - (O 3), four - (P 4), eight-atomic (S 8) molecules. The vast majority of solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).

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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 a substance is therefore solid because 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, and 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, here are 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 electrical charges of the ions themselves, as a result of which an electromagnetic field is formed, which determines the properties of substances having an ionic crystal lattice. And these are refractoriness, hardness, density and the ability to conduct electric current. A typical example of an ionic crystal lattice is table salt.

Atomic crystal lattice

Substances with an atomic crystal lattice, as a rule, have strong atoms in their nodes. A covalent bond occurs when two identical atoms share fraternal electrons with each other, thus forming a common pair of electrons for neighboring atoms. Because of this, covalent bonds bind atoms tightly and evenly in a strict order - perhaps this is the most characteristic structure of the atomic crystal lattice. Chemical elements with similar bonds can boast of their hardness and high melting point. The atomic crystal lattice has such chemical elements like diamond, silicon, germanium, boron.

Molecular crystal lattice

The molecular type of crystal lattice is characterized by the presence of stable and closely packed molecules. They are located at the nodes of the crystal lattice. In these nodes they are held by van der Waltz 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 a metal crystal lattice is more flexible and ductile than the ionic one, although in appearance they are very similar. Distinctive feature it is the presence of positively charged cations (metal ions) at lattice sites. Between the nodes live electrons that participate in the creation of the 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, heat and electrical conductivity, fusibility.

Crystal lattices, video

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

Matter, 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, turns into a liquid at a temperature of -194 °C blue color, and at a temperature of -218.8 °C it hardens into a snow-like mass consisting of blue crystals.

Rice. 70.
Physical 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 turn into a fluid state. Amorphous substances include most plastics (for example, polyethylene), wax, chocolate, plasticine, various resins and chewing gum(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 framework is formed, called a crystal lattice. The points at which crystal particles are located are called lattice nodes.

The nodes of an imaginary crystal lattice may contain monatomic ions, atoms, and molecules. These particles perform oscillatory movements. With increasing 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
Position of elements in the Periodic Table of D. I. Mendeleev and types of crystal lattices of their simple substances

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

Ionic lattices are called crystal lattices whose nodes contain ions. They are formed by substances with ionic bonds, which can bind both simple ions Na +, Cl -, and complex ions, OH -. Consequently, ionic crystal lattices have salts, bases (alkalis), and 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 ions in such a crystal are very strong. Therefore, substances with an ionic lattice have relatively high hardness and strength, they are refractory and nonvolatile.

Rice. 72.
Ionic crystal lattice (sodium chloride)

Atomic lattices are called crystal lattices, the nodes of which contain individual atoms. In such lattices, the atoms are connected to each other by very strong covalent bonds.

Rice. 73.
Atomic crystal lattice (diamond)

Diamond has this type of crystal lattice (Fig. 73) - one of the allotropic modifications of carbon. Diamonds that have been cut and polished are called brilliants. They are widely used in jewelry (Fig. 74).

Rice. 74.
Two imperial crowns with diamonds:
a - 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, for example, silica, quartz, sand, rock crystal, which include silicon (IV) oxide 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 are crystal lattices in which molecules are located at the nodes. The chemical bonds in these molecules can be both covalent polar (hydrogen chloride HCl, water H20) and covalent nonpolar (nitrogen N2, ozone 03). Despite the fact that the atoms inside the molecules are connected by very strong covalent bonds, weak intermolecular forces of attraction act between the molecules themselves. Therefore, substances with molecular crystal lattices have low hardness, low temperatures melting, 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 mono- (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-atomic (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 sites of such lattices there are atoms and ions (either atoms or ions, into which metal atoms easily turn, giving up their outer electrons for common use). This internal structure metals determines their characteristic physical properties: malleability, ductility, electrical and thermal conductivity, metallic luster.

Rice. 77.
Metal crystal lattice (iron)

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

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

Build a model of one of the crystal lattices.

For substances with a molecular structure, the open French chemist J. L. Proust (1799-1803) law of constancy of composition. Currently this law is formulated as follows:

Proust's Law is one of the basic laws of chemistry. However, for substances of non-molecular structure, such as ionic ones, this law is not always true.

Key words 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. Law of constancy of composition.

Work with computer

1. Refer to the electronic application. Study the lesson material and complete the assigned tasks.
2. Search on the Internet email addresses, which can serve as additional sources revealing the content of keywords and phrases in the paragraph. Offer your help to the teacher in preparing a new lesson - send a message by keywords and phrases in the next paragraph.

Questions and tasks

1. What state of aggregation will oxygen be in at -205 °C?
2. Remember the work of A. Belyaev “The Air Seller” and characterize the properties of solid oxygen using its description given in the book.
3. What type of substances (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 characteristic of diamond.
5. What type of iodine crystal lattice is it? List the physical properties characteristic 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 silicon product break into pieces upon impact, while a lead product only flattens out? In which of these cases does the chemical bond break down and in which does it not? Why?

Let's talk about solids. Solids can be divided into two large groups: amorphous And crystalline. We will separate them according to the principle of whether there is order or not.

IN amorphous substances the molecules are arranged randomly. There are no patterns in their spatial arrangement. Essentially, amorphous substances are very viscous liquids, so viscous that they are solid.

Hence the name: “a-” – negative particle, “morphe” – form. Amorphous substances include: glass, resins, wax, paraffin, soap.

The lack of order in the arrangement of particles determines the physical properties of amorphous bodies: they do not have fixed melting points. As they heat up, their viscosity gradually decreases, and they also gradually turn into a liquid state.

In contrast to amorphous substances, there are crystalline substances. The particles of a crystalline substance are spatially ordered. This correct structure of the spatial arrangement of particles in a crystalline substance is called crystal lattice.

Unlike amorphous bodies, crystalline substances have fixed melting points.

Depending on what particles are in lattice nodes, and what connections hold them together differentiate them: molecular, atomic, ionic And metal grates.

Why is it fundamentally important to know what kind of crystal lattice a substance has? What does it define? All. The structure determines how chemical and physical properties of a substance.

The simplest example: DNA. In all organisms on earth, it is built from the same set of structural components: four types of nucleotides. And what a variety of life. This is all determined by structure: the order in which these nucleotides are arranged.

Molecular crystal lattice.

A typical example is water in a solid state (ice). Entire molecules are located at lattice sites. And keep them together intermolecular interactions: hydrogen bonds, van der Waals forces.

These bonds are weak, so the molecular lattice is the most fragile, the melting point of such substances is low.

A good diagnostic sign: if a substance has normal conditions liquid or gaseous state and/or has an odor - then most likely this substance has a molecular crystal lattice. After all, the liquid and gaseous states are a consequence of the fact that the molecules on the surface of the crystal do not adhere well (the bonds are weak). And they are “blown away.” This property is called volatility. And the deflated molecules, diffusing in the air, reach our olfactory organs, which is subjectively felt as a smell.

They have a molecular crystal lattice:

1. Some simple substances of non-metals: I 2, P, S (that is, all non-metals that do not have an atomic lattice).
2. Almost all organic substances ( except salts).
3. And as mentioned earlier, substances under normal conditions are liquid, or gaseous (being frozen) and/or odorless (NH 3, O 2, H 2 O, acids, CO 2).

Atomic crystal lattice.

In the nodes of the atomic crystal lattice, in contrast to the molecular one, there are individual atoms. It turns out that the lattice is held together by covalent bonds (after all, they are the ones that bind neutral atoms).

A classic example is the standard of strength and hardness - diamond (by its chemical nature it is a simple substance - carbon). Contacts: covalent nonpolar, since the lattice is formed only by carbon atoms.

But, for example, in a quartz crystal (the chemical formula of which is SiO 2) there are Si and O atoms. Therefore, the bonds covalent polar.

Physical properties of substances with an atomic crystal lattice:

1. strength, hardness
2. high melting points (refractoriness)
3. non-volatile substances
4. insoluble (neither in water nor in other solvents)

All these properties are due to the strength of covalent bonds.

There are few substances in an atomic crystal lattice. There is no particular pattern, so you just need to remember them:

1. Allotropic modifications of carbon (C): diamond, graphite.
2. Boron (B), silicon (Si), germanium (Ge).
3. Only two allotropic modifications of phosphorus have an atomic crystal lattice: red phosphorus and black phosphorus. (y white phosphorus– molecular crystal lattice).
4. SiC – carborundum (silicon carbide).
5. BN – boron nitride.
6. Silica, rock crystal, quartz, river sand– all these substances have the composition SiO 2.
7. Corundum, ruby, sapphire - these substances have the composition Al 2 O 3.

Surely the question arises: C is both diamond and graphite. But they are completely different: graphite is opaque, stains, and conducts electricity, while diamond is transparent, does not stain, and does not conduct electricity. They differ in structure.

Both are atomic lattice, but different. Therefore, the properties are different.

Ionic crystal lattice.

Classic example: table salt: NaCl. At the lattice nodes there are individual ions: Na + and Cl – . The lattice is held in place by electrostatic forces of attraction between the ions (“plus” is attracted to “minus”), that is ionic bond.

Ionic crystal lattices are quite strong, but fragile; the melting temperatures of such substances are quite high (higher than those of metallic lattices, but lower than those of substances with an atomic lattice). Many are soluble in water.

As a rule, there are no problems with determining the ionic crystal lattice: where there is an ionic bond, there is an ionic crystal lattice. This: all salts, metal oxides, alkalis(and other basic hydroxides).

Metal crystal lattice.

The metal grating is sold in simple substances metals. Earlier we said that all the splendor of the metallic bond can only be understood in conjunction with the metallic crystal lattice. The hour has come.

The main property of metals: electrons on external energy level They are poorly held, so they are easily given away. Having lost an electron, the metal turns into a positively charged ion - a cation:

Na 0 – 1e → Na +

In a metal crystal lattice, processes of electron release and gain constantly occur: an electron is torn away from a metal atom at one lattice site. A cation is formed. The detached electron is attracted by another cation (or the same one): a neutral atom is formed again.

The nodes of a metal crystal lattice contain both neutral atoms and metal cations. And free electrons travel between the nodes:

These free electrons are called electron gas. They determine the physical properties of simple metal substances:

1. thermal and electrical conductivity
2. metallic shine
3. malleability, ductility

This is a metallic bond: metal cations are attracted to neutral atoms and free electrons “glue” it all together.

How to determine the type of crystal lattice.

P.S. There's something in school curriculum and the Unified State Exam program on this topic is something with which we do not entirely agree. Namely: the generalization that any metal-nonmetal bond is an ionic bond. This assumption was deliberately made, apparently to simplify the program. But this leads to distortion. The boundary between ionic and covalent bonds is arbitrary. Each bond has its own percentage of “ionicity” and “covalency”. The bond with a low-active metal has a small percentage of “ionicity”; it is more like a covalent one. But according to the Unified State Exam program, it is “rounded” towards the ionic one. This gives rise to sometimes absurd things. For example, Al 2 O 3 is a substance with an atomic crystal lattice. What kind of ionicity are we talking about here? Only covalent bond can hold atoms in this way. But according to the metal-non-metal standard, we classify this bond as ionic. And we get a contradiction: the lattice is atomic, but the bond is ionic. This is what oversimplification leads to.

What exists in nature is formed by a large number of identical particles that are connected to each other. All substances exist in three states of aggregation: gaseous, liquid and solid. When thermal movement is difficult (at low temperatures), as well as in solids, the particles are strictly oriented in space, which is manifested in their precise structural organization.

The crystal lattice of a substance is a structure with a geometrically ordered arrangement of particles (atoms, molecules or ions) at certain points in space. In various lattices, a distinction is made between the internodal space and the nodes themselves - the points at which the particles themselves are located.

There are four types of crystal lattice: metallic, molecular, atomic, ionic. The types of lattices are determined in accordance with the type of particles located at their nodes, as well as the nature of the connections between them.

A crystal lattice is called molecular if molecules are located at its nodes. They are related to each other by intermolecular relatively weak forces, called van der Waals, but the atoms themselves inside the molecule are connected in a significantly stronger or non-polar way). The molecular crystal lattice is characteristic of chlorine, solid hydrogen, and other substances that are gaseous at ordinary temperatures.

The crystals that form the noble gases also have molecular lattices consisting of monatomic molecules. Most organic solids have this structure. The number of which has a molecular structure is very small. These are, for example, solid hydrogen halides, natural sulfur, ice, simple solids and some others.

When heated, relatively weak intermolecular bonds are destroyed quite easily, therefore substances with such lattices have very low melting points and low hardness, they are insoluble or slightly soluble in water, their solutions practically do not conduct electric current, and are characterized by significant volatility. Minimum temperatures boiling and melting - for substances made of non-polar molecules.

A crystal lattice is called metallic, the nodes of which are formed by atoms and positive ions (cations) of the metal with free valence electrons (detached from the atoms during the formation of ions), randomly moving in the volume of the crystal. However, these electrons are essentially semi-free, since they can move freely only within the framework that is limited by a given crystal lattice.

Electrostatic electrons and positive metal ions are mutually attracted, which explains the stability of the metal crystal lattice. The collection of free moving electrons is called electron gas - it provides good electrical and When an electrical voltage appears, electrons rush to the positive particle, participating in the creation of electric current and interacting with ions.

The metallic crystal lattice is characteristic mainly of elemental metals, as well as of compounds of different metals with each other. The main properties that are inherent in metal crystals (mechanical strength, volatility, fluctuate quite strongly. However, such physical properties as plasticity, malleability, high electrical and thermal conductivity, and a characteristic metallic luster are characteristic only exclusively of crystals with a metal lattice.