Crystal lattice of sand. Types of crystal lattices

Solids exist in crystalline and amorphous states and are predominantly crystalline in structure. It is distinguished by the correct location of particles at precisely defined points, characterized by periodic repetition in the volume. If you mentally connect these points with straight lines, we get a spatial framework, which is called a crystal lattice. The concept of "crystal lattice" refers to a geometric pattern that describes the three-dimensional periodicity in the arrangement of molecules (atoms, ions) in crystalline space.

The locations of particles are called lattice nodes. There are internodal connections inside the frame. The type of particles and the nature of the connection between them: molecules, atoms, ions determine a total of four types: ionic, atomic, molecular and metallic.

If ions (particles with a negative or positive charge) are located at lattice sites, then this is an ionic crystal lattice, characterized by bonds of the same name.

These connections are very strong and stable. Therefore, substances with this type of structure have a fairly high hardness and density, are non-volatile and refractory. At low temperatures they act as dielectrics. However, when such compounds melt, the geometrically correct ionic crystal lattice (the arrangement of ions) is disrupted and the strength bonds decrease.

At a temperature close to the melting point, crystals with ionic bonds are already capable of conducting electric current. Such compounds are easily soluble in water and other liquids that consist of polar molecules.

An ionic crystal lattice is characteristic of all substances with an ionic type of bond - salts, metal hydroxides, binary compounds of metals with non-metals. has no directionality in space, because each ion is associated with several counterions at once, the strength of interaction of which depends on the distance between them (Coulomb's law). Ionic-bonded compounds have a non-molecular structure; they are solid substances with ionic lattices, high polarity, high melting and boiling points, and are electrically conductive in aqueous solutions. Compounds with ionic bonds in pure form practically never occurs.

The ionic crystal lattice is inherent in some hydroxides and oxides of typical metals, salts, i.e. substances with ionic

In addition to ionic bonds, there are metallic, molecular and covalent bonds in crystals.

Crystals that have a covalent bond are semiconductors or dielectrics. Typical examples of atomic crystals are diamond, silicon and germanium.

Diamond is a mineral, an allotropic cubic modification (form) of carbon. The crystal lattice of diamond is atomic and very complex. At the nodes of such a lattice there are atoms connected to each other by extremely strong covalent bonds. Diamond consists of individual carbon atoms, arranged one at a time in the center of a tetrahedron, the vertices of which are the four nearest atoms. Such a lattice is characterized by a face-centered cubic structure, which determines the maximum hardness of the diamond and is quite high temperature melting. There are no molecules in the diamond lattice - and the crystal can be viewed as one impressive molecule.

In addition, it is characteristic of silicon, solid boron, germanium and compounds of individual elements with silicon and carbon (silica, quartz, mica, river sand, carborundum). In general, there are relatively few representatives with an atomic lattice.

Instructions

As you can easily guess from the name itself, the metal type of lattice is found in metals. These substances are usually characterized by a high melting point, metallic luster, hardness, and are good conductors of electric current. Remember that lattice sites of this type contain either neutral atoms or positively charged ions. In the spaces 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. Positively and negatively charged ions alternate alternately at the sites of such lattices. Such substances are usually refractory and have low volatility. As you might guess, they have ion type.

The atomic type of crystal lattice is inherent in simple substances - nonmetals, which, when normal conditions are solid bodies. For example, sulfur, phosphorus,... At the sites of such lattices there are neutral atoms connected to each other by covalent chemical bonds. Such substances are characterized by refractoriness and insolubility in water. Some (for example, carbon in the form) have exceptionally high hardness.

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

Sources:

• grating type

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

You will need

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

Instructions

Place the glass tube vertically on a hard surface and drop the capillary through it several times, sealed end down. This helps compact 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 changes in the test substance as the temperature increases. Before and during heating, the thermometer should not touch the walls of the block or other very hot 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 decrease until it completely transforms into a liquid state. When performing the analysis, also look for changes 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 solid to liquid. At the end of the analysis, make a conclusion about the purity of the test substance.

Video on the topic

In crystals, chemical particles (molecules, atoms and ions) are arranged in in a certain order, under some conditions they form regular symmetrical polyhedra. There are four types crystal lattices- ionic, atomic, molecular and metallic.

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 three-dimensional formations in which the same structural element is repeated in all directions.

The correct shape of crystals is determined by their internal structure. If you replace molecules, atoms and ions in them with points instead of the centers of gravity of these particles, you get a three-dimensional regular distribution - . The repeating elements of its structure are called elementary cells, and the points are called 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 are. This type of crystal includes 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 capable of attaching new ions.

Atomic crystal lattices

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

Molecular crystals

Molecular crystal lattices are formed from molecules whose atoms are united by covalent bonds. Because of this, weak molecular forces act between molecules. Such crystals are characterized by low hardness, low melting point and high fluidity. The substances that they form, as well as their melts and solutions, do not conduct electric current well.

Metal crystal lattices

In metal crystal lattices, atoms are arranged with maximum density, their bonds are delocalized, and they extend throughout the entire crystal. Such crystals are opaque, have a metallic luster, are easily deformed, and are good conductors of electricity and heat.

This classification describes only limiting cases, most crystals inorganic substances belongs to intermediate types - molecular-covalent, covalent, etc. As an example, a graphite crystal has covalent-metallic bonds inside each layer, and molecular bonds between the layers.

Sources:

• alhimik.ru, Solids

Diamond is a mineral that belongs to one of the allotropic modifications of carbon. Distinctive feature its high hardness, which rightfully earns it the title of the hardest substance. Diamond is a fairly rare mineral, but at the same time it is the most widespread. Its exceptional hardness finds its application in mechanical engineering and industry.

Instructions

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

The carbon atom has sp3 hybridized orbitals that are 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 strongest 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.

Topics Unified State Exam codifier: Substances of molecular and non-molecular structure. Type of crystal lattice. Dependence of the properties of substances on their composition and structure.

Molecular kinetic theory

All molecules are made up of tiny particles– atoms. All currently discovered atoms are collected in the periodic table.

Atom- is the smallest, chemically indivisible particle of a substance that preserves it chemical properties. Atoms connect with each other chemical bonds. We have already looked at 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 in matter can connect.

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 apart from each other far(the distance between particles is much more sizes particles themselves), practically do not interact with each other, move in space chaotically and continuously, then we are dealing with gas .

If the particles are located close to each other, but chaotic, more interact with each other, perform intense 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 in an orderly manner, And interact more among themselves, but move only within one equilibrium position, practically without moving to others situation, then we are dealing with solid .

Most known chemical substances 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 - goes from a liquid state to hard, and at 100 o C it boils - turns into gas phase– water vapor. Moreover, 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 when high blood pressure and low temperatures, nitrogen and oxygen condense and pass into the liquid phase. Liquid nitrogen is actively used in industry. Sometimes isolated plasma, and also liquid crystals, as separate phases.

Many properties of individual substances and mixtures are explained mutual arrangement of particles in space relative to each other!

This article examines properties solids , depending on their structure. Basic physical properties solids: melting point, electrical conductivity, thermal conductivity, mechanical strength, ductility, etc.

Melting point - this is the temperature at which a substance passes from the solid phase to the liquid phase, and vice versa.

is the ability of a substance to deform without destruction.

Electrical conductivity is the ability of a substance to conduct current.

Current is the ordered movement of charged particles. Thus, current can only be carried out by substances that contain mobile charged particles. Based on their 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 substance, particles of a substance can be located chaotic, or more orderly O. If the particles of a solid are located in space chaotic, the substance is called amorphous. Examples of amorphous substances – coal, mica glass.

If the particles of a solid substance 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 we know 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; according to the geometric shape of the simplest cell of a crystal lattice - cubic, hexagonal, etc.

Depending on type of particles that form a crystal lattice , distinguish atomic, molecular, ionic and metal crystal structure .

Atomic crystal lattice

An atomic crystal lattice is formed when the nodes of the crystal are located atoms. The atoms are strongly 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 high valency, i.e. With a large number bonds with neighboring atoms (4 or more). As a rule, these are non-metals: simple substances - silicon, boron, carbon (allotropic modifications diamond, graphite), and their compounds (boron carbon, silicon oxide (IV), etc..). Since predominantly covalent chemical bonds occur between nonmetals, free electrons(like other charged particles) in substances with an atomic crystal lattice in most cases no. Therefore, such substances are usually conduct electricity very poorly, i.e. are dielectrics. This general patterns, from which there are a number of exceptions.

Communication between particles in atomic crystals: .

At the nodes of the crystal with an atomic crystal structure located atoms.

Phase state atomic crystals under normal conditions: as a rule, solids.

Substances, forming atomic crystals in the solid state:

1. Simple substances high valency (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- this is a lattice, at the nodes of which there are molecules. Holds molecules in 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 – fusible, fragile. How more power attraction between molecules, the higher the melting point of the substance. As a rule, the melting temperatures 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. A molecular crystal lattice, as a rule, is formed in solid form by acids, non-metal oxides, other binary compounds of non-metals, simple substances that form stable molecules (oxygen O 2, nitrogen N 2, water H 2 O, etc.), organic matter. As a rule, these are substances with a covalent polar (less often nonpolar) bond. Because electrons are involved in chemical bonds, substances with a molecular crystal lattice - dielectrics, do not conduct heat well.

Communication between particles in molecular crystals: m intermolecular, electrostatic or intermolecular forces of attraction.

At the nodes of the crystal with a molecular crystal structure located molecules.

Phase state molecular crystals under normal conditions: gases, liquids and solids.

Substances, forming in the solid state molecular crystals:

1. Simple nonmetallic substances that form small, strong molecules (O 2, N 2, H 2, S 8, etc.);
2. Complex substances (non-metal compounds) with polar covalent bonds (except for silicon and boron oxides, silicon and carbon compounds) - water H 2 O, sulfur oxide SO 3, etc.
3. Monatomic noble gases (helium, neon, argon, krypton 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 melting point):

— 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 crystal nodes – ions, we can talk about ionic crystal lattice . Typically, ionic crystals alternate positive ions(cations) and negative ions(anions), so the particles are held in the crystal forces of electrostatic attraction . Depending on the type of crystal and the type of ions forming the crystal, such substances can be quite durable and refractory. In the solid state, there are usually no mobile charged particles in ionic crystals. But when the crystal dissolves or melts, ions are released and can move under the influence of external electric field. Those. Only solutions or melts conduct current ionic crystals. The ionic crystal lattice is characteristic of substances with ionic chemical bond. Examples such substances - table salt NaCl, calcium carbonate– CaCO 3, etc. An 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 located ions.

Phase state ionic crystals under normal conditions: as a rule, solids.

Chemicals with ionic crystal lattice:

1. Salts (organic and inorganic), including ammonium salts (For example, ammonium chloride NH 4 Cl);
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 (refractoriness);

— solutions and melts of ionic crystals are current conductors;

— most compounds are soluble in polar solvents (water);

- solid phase state for most compounds under normal conditions.

And finally, metals are characterized special kind spatial structure – metal crystal lattice, which is due metal chemical bond . Metal atoms hold valence electrons rather weakly. In crystal formed by metal, occur simultaneously following processes: Some atoms give up electrons and become positively charged ions; these electrons move randomly in the crystal; some electrons are attracted to ions. These processes occur simultaneously and chaotically. Thus, ions arise , as in the formation of an ionic bond, and shared electrons are formed , as in the formation of a covalent bond. Free electrons move randomly and continuously throughout the entire volume of the crystal, like a gas. That's why they are sometimes called " electron gas " Due to the presence of a large number of mobile charged particles, metals conduct current and heat. The melting point of metals varies greatly. Metals are also characterized a peculiar metallic luster, malleability, i.e. the ability to change shape without destruction under strong mechanical stress, because chemical bonds are not destroyed.

Communication between particles : .

At the nodes of the crystal with metal grille located metal ions and atoms.

Phase state metals under normal conditions: usually solids(exception is mercury, a liquid under normal conditions).

Chemicals 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 usually 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 lack of a crystal lattice) allows one 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 this is, for example, carbon dioxide , for an atomic crystal lattice - diamond, for metal - copper, and for the ionic crystal lattice - table salt, sodium chloride NaCl.

Summary table on the structures of simple substances formed by chemical elements from the main subgroups of the periodic table (elements of the side subgroups are metals, therefore, have a metallic crystal lattice).

The final table of the relationship between the properties of substances and their structure:

Most solids have a crystalline structure. Crystal lattice built from repeating identical structural units, individual for each crystal. This structural unit is called the “unit cell”. In other words, the crystal lattice serves as a reflection of the spatial structure of a solid.

Crystal lattices can be classified in different ways.

I. According to the symmetry of crystals lattices are classified into cubic, tetragonal, rhombic, hexagonal.

This classification is convenient for assessing the optical properties of crystals, as well as their catalytic activity.

II. By the nature of the particles, located at lattice nodes and by type of chemical bond there is a distinction between them atomic, molecular, ionic and metal crystal lattices. The type of bond in a crystal determines the difference in hardness, solubility in water, the magnitude of the heat of solution and heat of fusion, and electrical conductivity.

Important characteristic crystal is crystal lattice energy, kJ/mol – the energy that must be expended to destroy a given crystal.

Molecular lattice

Molecular crystals consist of molecules held in certain positions of the crystal lattice by weak intermolecular bonds (van der Waals forces) or hydrogen bonds. These lattices are characteristic of substances with covalent bonds.

There are a lot of substances with a molecular lattice. This large number organic compounds(sugar, naphthalene, etc.), crystalline water (ice), solid carbon dioxide (“dry ice”), solid hydrogen halides, iodine, solid gases, including noble ones,

The energy of the crystal lattice is minimal for substances with non-polar and low-polar molecules (CH 4, CO 2, etc.).

Lattices formed by more polar molecules also have a higher crystal lattice energy. The greatest energy is possessed by lattices containing substances that form hydrogen bonds(H 2 O, NH 3).

Due to the weak interaction between molecules, these substances are volatile, fusible, have low hardness, do not conduct electric current (dielectrics) and have low thermal conductivity.

Atomic lattice

In nodes atomic crystal lattice there are atoms of one or various elements, interconnected by covalent bonds along all three axes. Such crystals which are also called covalent, are relatively few in number.

Examples of crystals of this type include diamond, silicon, germanium, tin, and also crystals complex substances, such as boron nitride, aluminum nitride, quartz, silicon carbide. All these substances have a diamond-like lattice.

The energy of the crystal lattice in such substances practically coincides with the energy of the chemical bond (200 – 500 kJ/mol). This determines their physical properties: high hardness, melting point and boiling point.

The electrically conductive properties of these crystals are varied: diamond, quartz, boron nitride are dielectrics; silicon, germanium – semiconductors; Metallic gray tin conducts electricity well.

In crystals with an atomic crystal lattice, it is impossible to distinguish a separate structural unit. The entire single crystal is one giant molecule.

Ionic lattice

In nodes ionic lattice positive and negative ions alternate, between which electrostatic forces act. Ionic crystals form compounds with ionic bonds, for example, sodium chloride NaCl, potassium fluoride and KF, etc. Ionic compounds may also include complex ions, for example, NO 3 -, SO 4 2 -.

Ionic crystals are also a giant molecule in which each ion is significantly influenced by all other ions.

The energy of the ionic crystal lattice can reach significant values. So, E (NaCl) = 770 kJ/mol, and E (BeO) = 4530 kJ/mol.

Ionic crystals have high melting and boiling points and high strength, but are brittle. Many of them conduct electricity poorly when room temperature(about twenty orders of magnitude lower than that of metals), but with increasing temperature an increase in electrical conductivity is observed.

Metal grate

Metal crystals give examples of the simplest crystal structures.

Metal ions in the lattice of a metal crystal can be approximately considered in the form of spheres. IN hard metals these balls are packed with maximum density, as indicated by the significant density of most metals (from 0.97 g/cm 3 for sodium, 8.92 g/cm 3 for copper to 19.30 g/cm 3 for tungsten and gold). The most dense packing of balls in one layer is a hexagonal packing, in which each ball is surrounded by six other balls (in the same plane). The centers of any three adjacent balls form an equilateral triangle.

Properties of metals such as high ductility and malleability indicate a lack of rigidity in metal gratings: their planes move quite easily relative to each other.

Valence electrons participate in the formation of bonds with all atoms and move freely throughout the entire volume of a piece of metal. This is indicated high values electrical conductivity and thermal conductivity.

In terms of crystal lattice energy, metals occupy an intermediate position between molecular and covalent crystals. The energy of the crystal lattice is:

Thus, the physical properties of solids depend significantly on the type of chemical bond and structure.

Structure and properties of solids

Characteristics	Crystals
Metal	Ionic	Molecular	Atomic
Examples	K, Al, Cr, Fe	NaCl, KNO3	I 2, naphthalene	diamond, quartz
Structural particles	Positive ions and mobile electrons	Cations and anions	Molecules	Atoms
Type of chemical bond	Metal	Ionic	In molecules – covalent; between molecules - van der Waals forces and hydrogen bonds	Between atoms - covalent
t melting	High	High	Low	Very high
boiling point	High	High	Low	Very high
Mechanical properties	Hard, malleable, viscous	Hard, brittle	Soft	Very hard
Electrical conductivity	Good guides	In solid form - dielectrics; in a melt or solution - conductors	Dielectrics	Dielectrics (except graphite)
Solubility
in the water	Insoluble	Soluble	Insoluble	Insoluble
in non-polar solvents	Insoluble	Insoluble	Soluble	Insoluble

(All definitions, formulas, graphs and equations of reactions are given on record.)

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Lesson type: Combined.

Objective of the lesson: To create conditions for the development of students’ ability to establish the cause-and-effect dependence of the physical properties of substances on the type of chemical bond and the type of crystal lattice, to predict the type of crystal lattice based on the physical properties of the substance.

Lesson objectives:

• To form concepts about the crystalline and amorphous state of solids, to familiarize students with various types crystal lattices, establish the dependence of the physical properties of a crystal on the nature of the chemical bond in the crystal and the type of crystal lattice, give students a basic understanding of the influence of the nature of the chemical bond and the types of crystal lattices on the properties of the substance.
• Continue to form the worldview of students, consider the mutual influence of the components of whole-structural particles of substances, as a result of which new properties appear, develop the ability to organize their educational work, and observe the rules of working in a team.
• Develop cognitive interest schoolchildren using problem situations;

Equipment: Periodic system D.I. Mendeleev, collection “Metals”, non-metals: sulfur, graphite, red phosphorus, crystalline silicon, iodine; Presentation “Types of crystal lattices”, models of crystal lattices different types(table salt, diamond and graphite, carbon dioxide and iodine, metals), samples of plastics and products made from them, glass, plasticine, computer, projector.

Lesson progress

1. Organizational moment.

The teacher welcomes students and records those who are absent.

2. Testing knowledge on the topics “Chemical bonding.” Oxidation state.”

Independent work (15 minutes)

3. Studying new material.

The teacher announces the topic of the lesson and the purpose of the lesson. (Slide 1,2)

Students write down the date and topic of the lesson in their notebooks.

Updating knowledge.

The teacher asks questions to the class:

1. What types of particles do you know? Do ions, atoms and molecules have charges?
2. What types of chemical bonds do you know?
3. What aggregative states of substances do you know?

Teacher:“Any substance can be a gas, a liquid or a solid. For example, water. Under normal conditions it is a liquid, but it can be steam and ice. Or oxygen under normal conditions is a gas, at a temperature of -1940 C it turns into liquid blue color, and at a temperature of -218.8°C it hardens into a snow-like mass consisting of crystals blue. In this lesson we will look at the solid state of substances: amorphous and crystalline.” (Slide 3)

Teacher: amorphous substances do not have a clear melting point - when heated, they gradually soften and turn into a fluid state. Amorphous substances include, for example, chocolate, which melts in both hands and mouth; chewing gum, plasticine, wax, plastics (examples of such substances are shown). (Slide 7)

Crystalline substances have a clear melting point and, most importantly, are characterized by the correct arrangement of particles at strictly defined points in space. (Slides 5,6) When these points are connected with straight lines, a spatial framework is formed, called a crystal lattice. The points at which crystal particles are located are called lattice nodes.

Students write down the definition in their notebooks: “A crystal lattice is a collection of points in space in which the particles that form a crystal are located. The points at which crystal particles are located are called lattice nodes.”

Depending on what types of particles are located at the nodes of this lattice, there are 4 types of lattices. (Slide 8) If there are ions at the nodes of a crystal lattice, then such a lattice is called ionic.

The teacher asks students questions:

– What will be the name of crystal lattices, in the nodes of which there are atoms and molecules?

But there are crystal lattices, at the nodes of which there are both atoms and ions. Such gratings are called metal gratings.

Now we will fill out the table: “Crystal lattices, type of bond and properties of substances.” As we fill out the table, we will establish the relationship between the type of lattice, the type of connection between particles and the physical properties of solids.

Let's consider the 1st type of crystal lattice, which is called ionic. (Slide 9)

– What is the chemical bond in these substances?

Look at the ionic crystal lattice (a model of such a lattice is shown). Its nodes contain positively and negatively charged ions. For example, a sodium chloride crystal is made up of positive sodium ions and negative chloride ions, forming a cube-shaped lattice. Substances with ionic crystal lattice include salts, oxides and hydroxides of typical metals. Substances with an ionic crystal lattice have high hardness and strength, they are refractory and non-volatile.

Teacher: The physical properties of substances with an atomic crystal lattice are the same as those of substances with an ionic crystal lattice, but often in superlatives– very hard, very durable. Diamond, whose atomic crystal lattice is the hardest substance of all natural substances. It serves as a standard for hardness, which is assessed using a 10-point system. highest score 10.(Slide 10). According to this type of crystal lattice, you yourself will introduce necessary information into the table after working independently with the textbook.

Teacher: Let's consider the 3rd type of crystal lattice, which is called metallic. (Slides 11,12) At the nodes of such a lattice there are atoms and ions, between which electrons move freely, connecting them into a single whole.

This internal structure metals and determines their characteristic physical properties.

Teacher: What physical properties of metals do you know? (malleability, plasticity, electrical and thermal conductivity, metallic luster).

Teacher: What groups are all substances divided into according to their structure? (Slide 12)

Let's consider the type of crystal lattice possessed by such well-known substances as water, carbon dioxide, oxygen, nitrogen and others. It's called molecular. (Slide14)

– What particles are located at the nodes of this lattice?

The chemical bond in molecules that are located at lattice sites can be either polar covalent or nonpolar covalent. Despite the fact that the atoms inside the molecule are connected by very strong covalent bonds, weak intermolecular attractive forces act between the molecules themselves. Therefore, substances with a molecular crystal lattice have low hardness, low melting points and are volatile. When gaseous or liquid substances turn into solids under special conditions, then they develop a molecular crystal lattice. Examples of such substances can be solid water - ice, solid carbon dioxide - dry ice. This lattice has naphthalene, which is used to protect woolen products from moths.

– What properties of the molecular crystal lattice determine the use of naphthalene? (volatility). As we see, not only solids can have a molecular crystal lattice. simple substances: noble gases, H 2 , O 2 , N 2 , I 2 , O 3 , white phosphorus P 4, but and complex: solid water, solid hydrogen chloride and hydrogen sulfide. Most solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).

The lattice sites contain nonpolar or polar molecules. Despite the fact that the atoms inside the molecules are connected by strong covalent bonds, weak intermolecular forces act between the molecules themselves.

Conclusion: The substances are fragile, have low hardness, low temperature melting, volatile.

Question: Which process is called sublimation or sublimation?

Answer: The transition of a substance from a solid state of aggregation directly to a gaseous state, bypassing the liquid state, is called sublimation or sublimation.

Demonstration of experiment: sublimation of iodine

Then students take turns naming the information they wrote down in the table.

Crystal lattices, type of bond and properties of substances.

Grille type	Types of particles at lattice sites	Type of communication between particles	Examples of substances	Physical properties of substances
Ionic	Ions	Ionic – strong bond	Salts, halides (IA, IIA), oxides and hydroxides of typical metals	Solid, strong, non-volatile, brittle, refractory, many soluble in water, melts conduct electric current
Nuclear	Atoms	1. Covalent non-polar – the bond is very strong 2. Covalent polar – the bond is very strong	Simple substances A: diamond (C), graphite (C), boron (B), silicon (Si). Complex substances : aluminum oxide (Al 2 O 3), silicon oxide (IV) – SiO 2	Very hard, very refractory, durable, non-volatile, insoluble in water
Molecular	Molecules	There are weak forces between molecules intermolecular attraction, but inside the molecules there is a strong covalent bond	Solids under special conditions that are gases or liquids under normal conditions (O 2, H 2, Cl 2, N 2, Br 2, H 2 O, CO 2, HCl); sulfur, white phosphorus, iodine; organic matter	Fragile, volatile, fusible, capable of sublimation, have low hardness
Metal	Atom ions	Metal - different strengths	Metals and alloys	Malleable, shiny, ductile, thermally and electrically conductive

Teacher: What conclusion can we draw from the work done on the table?

Conclusion 1: The physical properties of substances depend on the type of crystal lattice. Composition of the substance → Type of chemical bond → Type of crystal lattice → Properties of substances . (Slide 18).

Question: Which type of crystal lattice from those discussed above is not found in simple substances?

Answer: Ionic crystal lattices.

Question: What crystal lattices are characteristic of simple substances?

Answer: For simple substances - metals - a metal crystal lattice; for non-metals – atomic or molecular.

Working with the Periodic System D.I. Mendeleev.

Question: Where in Periodic table are metal elements found and why? Non-metal elements and why?

Answer : If you draw a diagonal from boron to astatine, then in the lower left corner of this diagonal there will be metal elements, because at the last energy level they contain from one to three electrons. These are elements I A, II A, III A (except boron), as well as tin and lead, antimony and all elements of secondary subgroups.

Non-metal elements are located in the upper right corner of this diagonal, because at the last energy level contain from four to eight electrons. These are the elements IV A, V A, VI A, VII A, VIII A and boron.

Teacher: Let's find non-metal elements whose simple substances have an atomic crystal lattice (Answer: C, B, Si) and molecular ( Answer: N, S, O , halogens and noble gases )

Teacher: Formulate a conclusion on how you can determine the type of crystal lattice of a simple substance depending on the position of the elements in D.I. Mendeleev’s Periodic Table.

Answer: For metal elements that are in I A, II A, IIIA (except boron), as well as tin and lead, and all elements of secondary subgroups in a simple substance, the type of lattice is metal.

For non-metal elements IV A and boron in a simple substance, the crystal lattice is atomic; and the elements V A, VI A, VII A, VIII A in simple substances have a molecular crystal lattice.

We continue to work with the completed table.

Teacher: Look carefully at the table. What pattern can be observed?

We listen carefully to the students’ answers, and then together with the class we draw a conclusion. Conclusion 2 (slide 17)

4. Fixing the material.

Test (self-control):

Substances that have a molecular crystal lattice, as a rule:
a) Refractory and highly soluble in water
b) Fusible and volatile
c) Solid and electrically conductive
d) Thermally conductive and plastic

The concept of “molecule” is not applicable to the structural unit of a substance:
a) Water
b) Oxygen
c) Diamond
d) Ozone

The atomic crystal lattice is characteristic of:
a) Aluminum and graphite
b) Sulfur and iodine
c) Silicon oxide and sodium chloride
d) Diamond and boron

If a substance is highly soluble in water, has a high melting point, and is electrically conductive, then its crystal lattice is:
a) Molecular
b) Nuclear
c) Ionic
d) Metal

5. Reflection.

6. Homework.

Characterize 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 → Interaction forces between the particles of the crystal → Physical properties due to the crystal lattice → Aggregate state of the substance under normal conditions → Examples.

Using the formulas of the given substances: SiC, CS 2, NaBr, C 2 H 2 - determine the type of crystal lattice (ionic, molecular) of each compound and, based on this, describe the expected physical properties of each of the four substances.