Everyone has an atomic crystal lattice. Solids: crystalline and amorphous

Engineering systems 20.09.2019

Engineering systems

Instruction

As you can easily guess from the name itself, the metallic type of lattice is found in metals. These substances are characterized, as a rule, by a high melting point, metallic luster, hardness, and are good conductors of electric current. Remember that at the sites of this type of lattice there are either neutral atoms or positively charged ions. In the gaps between the nodes there are electrons, the migration of which ensures the high electrical conductivity of such substances.

Ionic type of crystal lattice. It should be remembered that it is also inherent in salts. Characteristic - crystals of the well-known table salt, sodium chloride. At the nodes of such lattices, positively and negatively charged ions alternate alternately. Such substances, as a rule, are refractory, with low volatility. As you might guess, they are of the ionic type.

Atomic type crystal lattice is inherent in simple substances - non-metals, which, when normal conditions represent solid bodies. For example, sulfur, phosphorus,. At the sites of such lattices there are neutral atoms bound to each other by a covalent chemical bond. Such substances are characterized by infusibility, insolubility in water. Some (for example, carbon in the form) - exceptionally high hardness.

Finally, the last type of lattice is molecular. It occurs in substances that are under normal conditions in liquid or gaseous form. As again, it can be easily understood from, at the nodes of such lattices there are molecules. They can be either non-polar (for simple gases such as Cl2, O2) or polar (the most famous example– H2O water). Substances with this type of lattice do not conduct current, are volatile, and have low melting points.

Sources:

lattice type

Temperature melting the solid is measured to determine its degree of purity. Impurities in a pure substance usually lower the temperature melting or increase the interval in which the compound melts. The capillary method is the classic method for monitoring impurities.

You will need

- test substance;
- glass capillary sealed at one end (diameter 1 mm);
- a glass tube with a diameter of 6-8 mm and a length of at least 50 cm;
- heated block.

Instruction

Stand the glass tube vertically on a hard surface and drop the capillary through it several times with the sealed end down. This contributes to the compaction of the substance. To determine the temperature, the column of the substance in the capillary should be about 2-5 mm.

Place the capillary thermometer in the heated block and observe the change in the test substance as the temperature rises. The thermometer before and during heating should not touch the walls of the block and other strongly heated surfaces, otherwise it may burst.

Note the temperature at which the first drops appear in the capillary (beginning melting), and the temperature at which the last substances disappear (end melting). In this interval, the substance begins to subside until the complete transition to the liquid state. When analyzing, also pay attention to the change or decomposition of the substance.

Repeat measurements 1-2 more times. Present the results of each measurement in the form of the corresponding temperature interval during which the substance passes from a solid to a liquid state. At the end of the analysis, make a conclusion about the purity of the test substance.

crystals

The crystalline state is characterized by the presence of long-range order in the arrangement of particles, as well as the symmetry of the crystal lattice. Solid crystals are called three-dimensional formations in which the same structural element is repeated in all directions.

correct form crystals is due to their internal structure. If we replace molecules, atoms and ions in them with points instead of the centers of gravity of these particles, we get a three-dimensional regular distribution - . The repeating elements of its structure are called elementary cells, and the points are called the nodes of the crystal lattice. There are several types of crystals depending on the particles that form them, as well as on the nature chemical bond between them.

Ionic crystal lattices

Ionic crystals form anions and cations, between which there is. To this type crystals include salts of most metals. Each cation is attracted to the anion and repelled by other cations, so it is impossible to isolate single molecules in an ionic crystal. The crystal can be considered as one huge one, and its size is not limited, it is able to attach new ions.

Atomic crystal lattices

In atomic crystals, individual atoms are united by covalent bonds. Like ionic crystals, they can also be viewed as huge molecules. At the same time, atomic crystals are very hard and durable, they do not conduct electricity and heat well. They are practically insoluble, they are characterized by low reactivity. Substances with atomic lattices melt at very high temperatures.

molecular crystals

Molecular crystal lattices are formed from molecules, the atoms of which are united by covalent bonds. Because of this, weak molecular forces act between the molecules. Such crystals are characterized by low hardness, low melting point and high fluidity. The substances they form, as well as their melts and solutions, are poor conductors. electricity.

Metallic crystal lattices

In the crystal lattices of metals, atoms are located with a maximum density, their bonds are delocalized, they extend to the entire crystal. Such crystals are opaque, have a metallic luster, are easily deformed, and conduct electricity and heat well.

This classification describes only limiting cases, most crystals do not organic matter belongs to intermediate types - molecular-covalent, covalent-, etc. An example is a graphite crystal, inside each layer it has covalent-metal bonds, and between layers - molecular.

Sources:

alchemik.ru, Solids

Diamond is a mineral belonging to one of the allotropic modifications of carbon. Its distinctive feature is its high hardness, which rightfully earns it the title of the hardest substance. Diamond is enough rare mineral, but also the most widely used. Its exceptional hardness finds its application in mechanical engineering and industry.

Instruction

Diamond has an atomic crystal lattice. The carbon atoms that form the basis of the molecule are arranged in the form of a tetrahedron, due to which the diamond has such high strength. All atoms are connected by strong covalent bonds, which are formed based on the electronic structure of the molecule.

The carbon atom has sp3 hybridization of orbitals, which are located at an angle of 109 degrees and 28 minutes. The overlap of hybrid orbitals occurs in a straight line in the horizontal plane.

Thus, when the orbitals overlap at such an angle, a centered one is formed, which belongs to the cubic system, so we can say that diamond has a cubic structure. This structure is considered one of the most durable in nature. All tetrahedra form a three-dimensional network of layers of six-membered rings of atoms. Such a stable network of covalent bonds and their three-dimensional distribution leads to additional strength of the crystal lattice.

A substance, as you know, can exist in three states of aggregation: gaseous, liquid and solid (Fig. 70). For example, oxygen, which normal conditions It is a gas, 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.

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 correct location 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 to 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

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

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

Work with computer

Refer to the electronic application. Study the material of the lesson and complete the suggested tasks.
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Questions and tasks

In what state of aggregation will oxygen be at -205 ° C?
Remember the work of A. Belyaev "The seller of air" and characterize the properties of solid oxygen using its description given in the book.
What type of substance (crystalline or amorphous) are plastics? What properties of plastics underlie their industrial applications?
What type of diamond crystal lattice is it? List the physical properties of a diamond.
What type of crystal lattice is iodine? List the physical properties of iodine.
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.

Stable for substances at low temperatures 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, minicomputers, 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.

Between the position of the element in periodic system and the crystal lattice of its corresponding simple substance there is a close relationship.

The simple substances of the remaining elements have a metallic crystal lattice.

FIXING

Study the lecture material, answer the following questions in writing in your 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 widely 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

Solids usually have crystal 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 a 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 mutual arrangement particles, but not their sizes.

The number of nearest neighboring particles that are 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 6. So, in a sodium chloride crystal, it is impossible to isolate individual salt molecules. They are not here. The whole crystal should be considered as a giant macromolecule consisting of an equal number of Na + and Cl - ions, Na n Cl n , where n - big 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. Number 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 lattice.