Types of chemical lattices. Types of crystal lattices

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

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

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

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

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

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

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

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

Debyegram registration scheme.

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

Topics of the Unified State Examination 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 called atoms. All currently discovered atoms are collected in the periodic table.

Atom is the smallest, chemically indivisible particle of a substance that retains its 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 greater than the size of the 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, make 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 at high pressure and low temperature, nitrogen and oxygen condense and pass into the liquid phase. Liquid nitrogen is actively used in industry. Sometimes isolated plasma, and 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 of solids, depending on their structure. Basic physical properties of solids: melting point, electrical conductivity, thermal conductivity, mechanical strength, ductility, etc.

Melting temperature - 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 substance 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 the 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 of 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. These are general patterns, to 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:

Simple substances high valency (located in the middle of the periodic table): boron, carbon, silicon, etc.
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. The greater the force of 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 substances. 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:

Simple nonmetallic substances that form small, strong molecules (O 2, N 2, H 2, S 8, etc.);
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.
Monatomic noble gases (helium, neon, argon, krypton and etc.);
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, the ions are released and can move under the influence of an 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 - 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.

Chemical substances with ionic crystal lattice:

Salts (organic and inorganic), including ammonium salts (For example, ammonium chloride NH 4 Cl);
Bases;
Metal oxides;
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 by a special type of spatial structure - metal crystal lattice, which is due metal chemical bond . Metal atoms hold valence electrons rather weakly. In a crystal formed by a metal, the following processes occur simultaneously: 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).

Chemical substances 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. To roughly compare 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 - 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 crystal structure, in which the particles from which it is “built” are in a certain order, thereby creating crystal lattice. It is built from repeating identical structural units - unit cells, which communicates with neighboring cells, forming additional nodes. As a result, there are 14 different crystal lattices.

Types of crystal lattices.

Depending on the particles that stand at the lattice nodes, they are distinguished:

metal crystal lattice;
ionic crystal lattice;
molecular crystal lattice;
macromolecular (atomic) crystal lattice.

Metallic bond in crystal lattices.

Ionic crystals have increased fragility, because a shift in the crystal lattice (even a slight one) leads to the fact that like-charged ions begin to repel each other, and bonds break, cracks and splits form.

Molecular bonding of crystal lattices.

The main feature of the intermolecular bond is its “weakness” (van der Waals, hydrogen).

This is the structure of ice. Each water molecule is connected by hydrogen bonds to 4 molecules surrounding it, resulting in a tetrahedral structure.

Hydrogen bonding explains the high boiling point, melting point and low density;

Macromolecular connection of crystal lattices.

There are atoms at the nodes of a crystal lattice. These crystals are divided into 3 types:

frame;
chain;
layered structures.

Frame structure diamond is one of the hardest substances in nature. The carbon atom forms 4 identical covalent bonds, which indicates the shape of a regular tetrahedron ( sp 3 - hybridization). Each atom has a lone pair of electrons, which can also bond with neighboring atoms. As a result, a three-dimensional lattice is formed, in the nodes of which there are only carbon atoms.

It takes a lot of energy to destroy such a structure; the melting point of such compounds is high (for diamond it is 3500°C).

Layered structures speak of the presence of covalent bonds within each layer and weak van der Waals bonds between the layers.

Let's look at an example: graphite. Each carbon atom is in sp 2 - hybridization. The 4th unpaired electron forms a van der Waals bond between the layers. Therefore, the 4th layer is very mobile:

The bonds are weak, so they are easy to break, which can be observed in a pencil - “writing property” - the 4th layer remains on the paper.

Graphite is an excellent conductor of electric current (electrons are able to move along the plane of the layer).

Chain structures have oxides (for example, SO 3 ), which crystallizes in the form of shiny needles, polymers, some amorphous substances, silicates (asbestos).

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Lesson type: Combined.

The purpose 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 of crystal lattices, to 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, to give students basic ideas about the influence of the nature of chemical bonds and types of crystal lattices on the properties of matter .
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.
To develop the cognitive interest of 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 of different types (table salt, diamond and graphite, carbon dioxide and iodine, metals), samples of plastics and products made from them, glass, plasticine, computer, projector.

During the classes

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:

What types of particles do you know? Do ions, atoms and molecules have charges?
What types of chemical bonds do you know?
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 a blue liquid, and at a temperature of -218.8 ° C it solidifies into a snow-like mass consisting of blue crystals. 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 to a superlative degree - very hard, very durable. Diamond, which has an atomic crystal lattice, is the hardest substance of all natural substances. It serves as a standard of hardness, which, according to a 10-point system, is rated with the highest score of 10. (Slide 10). For this type of crystal lattice, you yourself will enter the necessary information into the table by working with the textbook yourself.

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 of metals 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 forces of attraction 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 melting point, and are 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 are the metal elements located in the Periodic Table 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 they 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.

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 melting points (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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