Solids, as a rule, have a crystalline structure. It is characterized by the correct arrangement of particles at strictly defined points in space. When these points are mentally connected by intersecting straight lines, a spatial frame is formed, which is called crystal lattice.
The points where the particles are placed are called lattice nodes. The nodes of an imaginary lattice can contain ions, atoms or molecules. They make oscillatory movements. With an increase in temperature, the amplitude of oscillations increases, which manifests itself in the thermal expansion of bodies.
Depending on the type of particles and the nature of the connection between them, four types of crystal lattices are distinguished: ionic, atomic, molecular and metallic.
Crystal lattices consisting of ions are called ionic. They are formed by substances with ionic bonds. An example is the sodium chloride crystal, in which, as already noted, each sodium ion is surrounded by six chloride ions, and each chloride ion by six sodium ions. This arrangement corresponds to the densest packing if the ions are represented as balls placed in a crystal. Very often, crystal lattices are depicted as shown in Fig, where only the mutual arrangement of particles is indicated, but not their sizes.
The number of nearest neighboring particles closely adjacent to a given particle in a crystal or in a single molecule is called coordination number.
In the sodium chloride lattice, the coordination numbers of both ions are equal to 6. So, in a sodium chloride crystal, it is impossible to isolate individual salt molecules. They are not here. The entire crystal should be considered as a giant macromolecule consisting of an equal number of Na + and Cl - ions, Na n Cl n , where n is a large number. The bonds between ions in such a crystal are very strong. Therefore, substances with an ionic lattice have a relatively high hardness. They are refractory and low volatility.
The melting of ionic crystals leads to a violation of the geometrically correct orientation of the ions relative to each other and a decrease in the strength of the bond between them. Therefore, their melts conduct electric current. Ionic compounds, as a rule, are readily soluble in liquids consisting of polar molecules, such as water.
Crystal lattices, at the nodes of which there are individual atoms, are called atomic. Atoms in such lattices are interconnected by strong covalent bonds. An example is diamond, one of the modifications of carbon. A diamond is made up of carbon atoms, each bonded to four neighboring atoms. The coordination number of carbon in diamond is 4 
. In the lattice of diamond, as in the lattice of sodium chloride, there are no molecules. The whole crystal should be considered as a giant molecule. The atomic crystal lattice is characteristic of solid boron, silicon, germanium, and compounds of certain elements with carbon and silicon.
Crystal lattices consisting of molecules (polar and non-polar) are called molecular.
Molecules in such lattices are interconnected by relatively weak intermolecular forces. Therefore, substances with a molecular lattice have low hardness and low melting points, are insoluble or slightly soluble in water, their solutions almost do not conduct electric current. The number of inorganic substances with a molecular lattice is small.
Examples of them are ice, solid carbon monoxide (IV) ("dry ice"), solid hydrogen halides, solid simple substances formed by one- (noble gases), two- (F 2, Cl 2, Br 2, I 2, H 2 , O 2, N 2), three- (O 3), four- (P 4), eight- (S 8) atomic molecules. The molecular crystal lattice of iodine is shown in Fig. 
. Most crystalline organic compounds have a molecular structure.
As we already know, matter can exist in three states of aggregation: gaseous, solid and liquid. Oxygen, which under normal conditions is in a gaseous state, at a temperature of -194 ° C is converted into a bluish liquid, and at a temperature of -218.8 ° C it turns into a snowy mass with blue crystals.
The temperature interval for the existence of a substance in the solid state is determined by the boiling and melting points. Solids are crystalline and amorphous.
At amorphous substances there is no fixed melting point - when heated, they gradually soften and become fluid. In this state, for example, there are various resins, plasticine.
Crystalline substances differ in the regular arrangement of the particles of which they are composed: atoms, molecules and ions, at strictly defined points in space. When these points are connected by straight lines, a spatial frame is created, it is called a crystal lattice. The points where the crystal particles are located are called lattice nodes.
At the nodes of the lattice we imagine, there can be ions, atoms and molecules. These particles oscillate. When the temperature increases, the range of these fluctuations also increases, which leads to thermal expansion of the 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 called such crystal lattices, at the nodes of which ions are located. They are formed by substances with an ionic bond, which can be associated with 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 there is an ionic chemical bond. Let's consider a crystal of sodium chloride, it consists of positively alternating Na+ and negative CL- ions, together they form a lattice in the form of a cube. The bonds between ions in such a crystal are extremely stable. Because of this, substances with an ionic lattice have a relatively high strength and hardness, they are refractory and non-volatile.
nuclear crystal lattices are called such crystal lattices, at the nodes of which there are individual atoms. In such lattices, atoms are interconnected 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 that contain silicon oxide (IV) - SiO 2: silica, quartz, sand, rock crystal.
The vast majority of substances with an atomic crystal lattice have very high melting points (for diamond it exceeds 3500 ° C), such substances are strong and hard, practically insoluble.
Molecular called such crystal lattices, at the nodes of which molecules are located. Chemical bonds in these molecules can also be either 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 are 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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Since ancient times, metals have played a huge role in the development of mankind. Implementing them in everyday life made a real revolution both in the ways of processing materials, and in human perception of the surrounding reality. Modern industry and agriculture, transport and infrastructure are impossible without the use of metals, the use of their useful qualities and properties. These qualities, in turn, are determined by the internal structure of this class of chemical compounds, which is based on the crystal lattice.
The concept and essence of the crystal lattice
From the point of view of the internal structure, any substance can be in one of three states - liquid, gaseous and solid. Moreover, it is the latter that is characterized by the greatest stability, due to the fact that the crystal lattice implies not only a clear arrangement of atoms or molecules in strictly defined places, but also the need to apply a sufficiently large force to break the bonds between these elementary particles.
Features of the ionic lattice
The structure of any substance in the solid state necessarily implies the periodic repetition of molecules and atoms in three dimensions at once. In this case, depending on what is at the key points, the crystal lattice can be ionic, atomic, molecular and metallic. As for the first variety, here the basic components are charged ions of opposite polarity, between which the so-called Coulomb forces arise and act. In this case, the interaction force is directly dependent on the radii of charged particles.
Such a grid is complex system, consisting of metal cations, in the space between which negatively charged electrons move. It is the presence of these elementary particles that gives the lattice stability and hardness, because they serve as a kind of compensators for positively charged cations.
Strength and weakness of the atomic lattice
Quite interesting from the point of view of the structure is the atomic crystal lattice. Already from the name, we can conclude that atoms are located in its nodes, held by covalent bonds. Many scientists in last years attribute this type of interaction to the family of inorganic polymers, since the structure of this molecule is largely determined by the valency of its constituent atoms.
Main characteristics of the molecular lattice
The molecular crystal lattice is the least stable of all presented. The thing is that the level of interaction of the molecules located in its nodes is extremely low, and the energy potential is determined by a number of factors, in which the main role is played by dispersion, induction and orientation forces.
Influence of the crystal lattice on the properties of objects
Thus, the crystal lattice largely determines the properties of a substance. For example, atomic crystals melt at extremely high temperatures and have increased hardness, while substances with a metallic lattice are excellent conductors.
Which under normal conditions is a gas, at a temperature of -194 ° C turns into a liquid blue color, i at a temperature of -218.8º C hardens into a snow-like mass, consisting of blue crystals.
In this section, we will consider how the features of chemical bonds affect the properties of solids. The temperature interval for the existence of a substance in the solid state is determined by its boiling and melting points. Solids are divided into crystalline and amorphous.
Amorphous substances do not have a clear melting point - when heated, they gradually soften and become fluid. In the amorphous state, for example, there is plasticine or various resins.
Crystalline substances are characterized by the correct arrangement of the particles of which they are composed: atoms, molecules and ions. - at strictly defined points in space. When these points are connected by straight lines, a spatial frame is formed, which is called the crystal lattice. The points at which the particles of the crystal are placed are called lay out the lattice.
The nodes of an imaginary lattice can contain ions, atoms and 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 bond between them, four types of crystal lattices are distinguished: ionic, atomic, molecular, and metallic (Table 6).
Simple substances of the remaining elements, not presented in Table 6, 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 SO 2- 4, OH-. Therefore, ionic crystal lattices have salts, some metal oxides and hydroxides, that is, those substances in which an ionic chemical bond exists. For example, a sodium chloride crystal is built from alternating positive Na+ and negative Cl- ions, forming a cube-shaped lattice. The bonds between ions in such a crystal are very stable. Therefore, substances with an ionic lattice structure have a relatively high hardness and strength, they are refractory and non-volatile.
Atomic crystals are poured into crystal lattices, at the nodes of which there are individual atoms. In such lattices, the atoms are interconnected by very strong covalent bonds. An example of substances with this type of crystal lattice is diamond, one of the allotropic modifications of carbon.
The number of substances with an atomic crystal lattice is not very large. These include crystalline boron, silicon and germanium, as well as complex substances, for example, those that include silicon oxide (IV) - SlO2: silica, quartz, sand, rock crystal.
Most substances with an atomic crystal lattice have very high melting points (for example, in diamond it is over 3500 ºС), 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 polar and non-polar. Despite the fact that the atoms inside the molecules are connected by very strong covalent bonds, weak forces of molecular attraction act 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) - "dry ice", solid hydrogen chloride and hydrogen sulfide, solid simple substances formed by one- (noble gases), two-, three- (O3), four- (P4). eight-atom molecules. Most solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).
Substances with a metallic bond have metallic crystal lattices. 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, and a characteristic metallic luster.
For substances having a molecular structure, the law of composition constancy discovered by the French chemist J. L. Proust (1799-1803) is valid. At present, this law is formulated as follows: “Molecular chemical compounds, regardless of the method of their preparation, have a constant composition and properties. Proust's law is one of the fundamental laws of chemistry. However, for substances with a non-molecular structure, for example, ionic, this law is not always valid.
1. Solid, liquid and gaseous states of matter.
2. Solids: amorphous and crystalline.
3. Crystal lattices: atomic, ionic, metallic and molecular.
4. The law of constancy of the composition.
What properties of naphthalene underlie its use to protect woolen products from moths?
What qualities of amorphous bodies are applicable to the description of the character traits of individual people?
Why was aluminum discovered by the Danish scientist K. X. Oersted in 1825 treated as precious metals for a long time?
Remember the work of A. Belyaev "The seller of air" and characterize the properties of solid oxygen using its description given in the book.
Why does the melting point of metals vary over a very wide range? To prepare an answer to this question, use additional literature.
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?
The structure of matter.
It is not individual atoms or molecules that enter into chemical interactions, but substances.
Our task is to get acquainted with the structure of matter.
At low temperatures for substances stable solid state.
☼ The hardest substance in nature is diamond. He is considered the king of all gems and precious stones. And its very name means in Greek "indestructible." Diamonds have long been regarded as miraculous stones. It was believed that a person wearing diamonds does not know stomach diseases, poison does not affect him, he retains his memory and cheerful mood until old age, enjoys royal favor.
☼ A diamond subjected to jewelry processing - cutting, polishing, is called a diamond.
During melting, as a result of thermal vibrations, the order of the particles is violated, they become mobile, while the nature of the chemical bond is not violated. Thus, there are no fundamental differences between the solid and liquid states.
Fluidity appears in the liquid (i.e., the ability to take the shape of a vessel).
liquid crystals.
Liquid crystals are open in late XIX century, but studied in the last 20-25 years. Many display devices modern technology, for example, some electronic clocks, mini-computers, run on liquid crystals.
In general, the words "liquid crystals" sound no less unusual than "hot ice". However, in fact, ice can also be hot, because. at pressures over 10,000 atm. water ice melts at temperatures above 2000 C. The unusual combination of "liquid crystals" is that the liquid state indicates the mobility of the structure, and the crystal suggests strict order.
If a substance consists of polyatomic molecules of an elongated or lamellar shape and having an asymmetric structure, then when it melts, these molecules are oriented in a certain way relative to each other (their long axes are parallel). In this case, the molecules can freely move parallel to themselves, i.e. the system acquires the fluidity characteristic of a liquid. At the same time, the system retains an ordered structure that determines the properties characteristic of crystals.
The high mobility of such a structure makes it possible to control it by very weak influences (thermal, electrical, etc.), i.e. purposefully change the properties of a substance, including optical ones, with very little energy, which is used in modern technology.
Types of crystal lattices.
Any chemical substance is formed by a large number of identical particles that are interconnected.
At low temperatures, when thermal motion is hindered, the particles are strictly oriented in space and form a crystal lattice.
Crystal cell is a structure with a geometrically correct arrangement of particles in space.
In the crystal lattice itself, nodes and internodal space are distinguished.
The same substance, depending on the conditions (p, t, ...) exists in different crystalline forms (i.e., they have different crystal lattices) - allotropic modifications that differ in properties.
For example, four modifications of carbon are known - graphite, diamond, carbyne and lonsdaleite.
☼ The fourth variety of crystalline carbon "lonsdaleite" is little known. It was found in meteorites and obtained artificially, and its structure is still being studied.
☼ Soot, coke, charcoal were classified as amorphous polymers of carbon. However, it has now become known that these are also crystalline substances.
☼ By the way, shiny black particles were found in the soot, which they called "mirror carbon". Mirror carbon is chemically inert, heat-resistant, impervious to gases and liquids, has smooth surface and absolute compatibility with living tissues.
☼ The name of graphite comes from the Italian "graffito" - I write, I draw. Graphite is a dark-gray crystals with a slight metallic sheen, has a layered lattice. Separate layers of atoms in a graphite crystal, relatively weakly bonded to each other, are easily separated from each other.
TYPES OF CRYSTAL LATTICES
Properties of substances with different crystal lattices (table)
If the crystal growth rate is low upon cooling, a glassy state (amorphous) is formed.
The relationship between the position of an element in the Periodic system and the crystal lattice of its simple substance.
There is a close relationship between the position of an element in the periodic table and the crystal lattice of its corresponding elementary substance.
The simple substances of the remaining elements have a metallic crystal lattice.
FIXING
Study the material of the lecture, answer the next questions writing in a notebook:
- What is a crystal lattice?
- What types of crystal lattices exist?
- Describe each type of crystal lattice according to the plan:
What is in the nodes of the crystal lattice, structural unit → Type of chemical bond between the particles of the node → Forces of interaction between the particles of the crystal → Physical properties due to the crystal lattice → Aggregate state of matter under normal conditions → Examples
Complete the tasks on this topic:
- What type of crystal lattice do the following substances commonly used in everyday life have: water, acetic acid (CH3 COOH), sugar (C12 H22 O11 ), potash fertilizer (KCl), river sand (SiO2 ) - melting point 1710 0C, ammonia (NH3 ) , salt? Make a generalized conclusion: what properties of a substance can determine the type of its crystal lattice?
According to the formulas of the given substances: SiC, CS2, NaBr, C2 H2 - determine the type of crystal lattice (ionic, molecular) of each compound and, based on this, describe the physical properties of each of the four substances.
Trainer number 1. "Crystal Grids"
Trainer number 2. "Test tasks"
Test (self-control):
1) Substances having a molecular crystal lattice, as a rule:
a). refractory and highly soluble in water
b). fusible and volatile
in). Solid and electrically conductive
G). Thermally conductive and plastic
2) The concept of "molecule" is not applicable in relation to the structural unit of a substance:
b). oxygen
in). diamond
3) The atomic crystal lattice is characteristic for:
a). aluminum and graphite
b). sulfur and iodine
in). silicon oxide and sodium chloride
G). diamond and boron
4) If a substance is highly soluble in water, has a high melting point, is electrically conductive, then its crystal lattice:
BUT). molecular
b). nuclear
in). ionic
G). metallic