Crystal lattices in chemistry. Types of crystal lattices

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Lesson type: Combined.

The main goal of the lesson: To give students specific ideas about amorphous and crystalline substances, types crystal lattices, establish the relationship between the structure and properties of substances.

Lesson objectives.

Educational: 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 properties of matter, give students an idea of ​​the law of constancy of composition.

Educational: 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.

Developmental: develop the cognitive interest of schoolchildren using problem situations; improve students’ abilities to establish the cause-and-effect dependence of the physical properties of substances on chemical bonds and the type of crystal lattice, to predict the type of crystal lattice based on the physical properties of the substance.

Equipment: Periodic table of D.I. Mendeleev, collection “Metals”, non-metals: sulfur, graphite, red phosphorus, oxygen; Presentation “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, resins, wax, chewing gum, chocolate, computer, multimedia installation, video experiment “Sublimation of benzoic acid”.

During the classes

1. Organizational moment.

The teacher welcomes students and records those who are absent.

Then he tells the topic of the lesson and the purpose of the lesson. Students write down the topic of the lesson in their notebook. (Slide 1, 2).

2. Checking homework

(2 students at the blackboard: Determine the type of chemical bond for substances with the formulas:

1) NaCl, CO 2, I 2; 2) Na, NaOH, H 2 S (write the answer on the board and include it in the survey).

3. Analysis of the situation.

Teacher: What does chemistry study? Answer: Chemistry is the science of substances, their properties and transformations of substances.

Teacher: What is a substance? Answer: Matter is what the physical body is made of. (Slide 3).

Teacher: What states of matter do you know?

Answer: There are three states of aggregation: solid, liquid and gaseous. (Slide 4).

Teacher: Give examples of substances that can exist in all three states of aggregation at different temperatures.

Answer: Water. At normal conditions water is in a liquid state, when the temperature drops below 0 0 C, water turns into a solid state - ice, and when the temperature rises to 100 0 C we get water vapor (gaseous state).

Teacher (addition): Any substance can be obtained in solid, liquid and gaseous form. In addition to water, these are metals that, under normal conditions, are in a solid state, when heated, they begin to soften, and at a certain temperature (t pl) they turn into a liquid state - they melt. With further heating, to the boiling point, the metals begin to evaporate, i.e. go into a gaseous state. Any gas can be converted into a liquid or solid state by lowering the temperature: for example, oxygen, which at a temperature (-194 0 C) turns into liquid blue color, and at a temperature (-218.8 0 C) it hardens into a snow-like mass consisting of crystals of blue color. Today in class we will look at the solid state of matter.

Teacher: Name what solid substances are on your tables.

Answer: Metals, plasticine, table salt: NaCl, graphite.

Teacher: What do you think? Which of these substances is excess?

Answer: Plasticine.

Teacher: Why?

Assumptions are made. If students find it difficult, then with the help of the teacher they come to the conclusion that plasticine, unlike metals and sodium chloride, does not have a certain melting point - it (plasticine) gradually softens and turns into a fluid state. Such, for example, is chocolate that melts in the mouth, or chewing gum, as well as glass, plastics, resins, wax (when explaining, the teacher shows the class samples of these substances). Such substances are called amorphous. (slide 5), and metals and sodium chloride are crystalline. (Slide 6).

Thus, two types of solids are distinguished : amorphous and crystalline. (slide7).

1) Amorphous substances do not have a specific melting point and the arrangement of particles in them is not strictly ordered.

Crystalline substances have a strictly defined melting point and, most importantly, are characterized correct location particles from which they are built: atoms, molecules and ions. These particles are located at strictly defined points in space, and if these nodes are connected by straight lines, then a spatial frame is formed - crystal cell.

The teacher asks problematic issues

How to explain the existence of solids with such different properties?

2) Why do crystalline substances split in certain planes upon impact, while amorphous substances do not have this property?

Listen to the students' answers and lead them to conclusion:

The properties of substances in the solid state depend on the type of crystal lattice (primarily on what particles are in its nodes), which, in turn, is determined by the type of chemical bond in a given substance.

Checking homework:

1) NaCl – ionic bond,

CO 2 – covalent polar bond

I 2 – covalent nonpolar bond

2) Na – metal bond

NaOH - ionic bond between Na + ion - (O and H covalent)

H 2 S - covalent polar

Frontal survey.

• Which bond is called ionic?
• What kind of bond is called covalent?
• Which bond is called a polar covalent bond? non-polar?
• What is electronegativity called?

Conclusion: There is a logical sequence, the relationship of phenomena in nature: Structure of the atom -> EO -> Types of chemical bonds -> Type of crystal lattice -> Properties of substances . (slide 10).

Teacher: Depending on the type of particles and the nature of the connection between them, they distinguish four types of crystal lattices: ionic, molecular, atomic and metallic. (Slide 11).

The results are presented in the following table - a sample table at the students’ desks. (see Appendix 1). (Slide 12).

Teacher: What do you think? For substances with what type of chemical bond will this type of lattice be characteristic?

Answer: Substances with ionic chemical bonds will be characterized by an ionic lattice.

Teacher: What particles will be at the lattice nodes?

Answer: Jonah.

Teacher: What particles are called ions?

Answer: Ions are particles that have a positive or negative charge.

Teacher: What are the compositions of ions?

Answer: Simple and complex.

Demonstration - model of sodium chloride (NaCl) crystal lattice.

Teacher's explanation: At the nodes of the sodium chloride crystal lattice there are sodium and chlorine ions.

In NaCl crystals there are no individual sodium chloride molecules. The entire crystal should be considered as a giant macromolecule consisting of an equal number of Na + and Cl - ions, Na n Cl n, where n is a large number.

The bonds between ions in such a crystal are very strong. Therefore, substances with an ionic lattice have a relatively high hardness. They are refractory, non-volatile, and fragile. Their melts conduct electric current (Why?) and easily dissolve in water.

Ionic compounds are binary compounds of metals (I A and II A), salts, and alkalis.

Demonstration of crystal lattices of diamond and graphite.

The students have graphite samples on the table.

Teacher: What particles will be located at the nodes of the atomic crystal lattice?

Answer: At the nodes of the atomic crystal lattice there are individual atoms.

Teacher: What chemical bond will arise between atoms?

Answer: Covalent chemical bond.

Teacher's explanations.

Indeed, at the sites of atomic crystal lattices there are individual atoms connected to each other by covalent bonds. Since atoms, like ions, can be arranged differently in space, crystals of different shapes are formed.

Atomic crystal lattice of diamond

There are no molecules in these lattices. The entire crystal should be considered as a giant molecule. An example of substances with this type of crystal lattices are allotropic modifications of carbon: diamond, graphite; as well as boron, silicon, red phosphorus, germanium. Question: What are these substances in composition? Answer: Simple in composition.

Atomic crystal lattices have not only simple, but also complex ones. For example, aluminum oxide, silicon oxide. All these substances have very high temperatures melting point (for diamond over 3500 0 C), strong and hard, non-volatile, practically insoluble in liquids.

Teacher: Guys, you have a collection of metals on your tables, let’s look at these samples.

Question: What chemical bond is characteristic of metals?

Answer: Metal. Bonding in metals between positive ions through shared electrons.

Question: What are the common physical properties Are they typical for metals?

Answer: Luster, electrical conductivity, thermal conductivity, ductility.

Question: Explain what is the reason that so many different substances have the same physical properties?

Answer: Metals have a single structure.

Demonstration of models of metal crystal lattices.

Teacher's explanation.

Substances with metallic bonds have metallic crystal lattices

At the sites of such lattices there are atoms and positive ions of metals, and valence electrons move freely in the volume of the crystal. The electrons electrostatically attract positive metal ions. This explains the stability of the lattice.

The teacher demonstrates and names the substances: iodine, sulfur.

Question: What do these substances have in common?

Answer: These substances are non-metals. Simple in composition.

Question: What is the chemical bond inside molecules?

Answer: The chemical bond inside molecules is covalent nonpolar.

Question: What physical properties are characteristic of them?

Answer: Volatile, fusible, slightly soluble in water.

Teacher: Let's compare the properties of metals and non-metals. Students answer that the properties are fundamentally different.

Question: Why are the properties of non-metals very different from the properties of metals?

Answer: Metals have metallic bonds, while non-metals have covalent, nonpolar bonds.

Teacher: Therefore, the type of lattice is different. Molecular.

Question: What particles are located at lattice points?

Answer: Molecules.

Demonstration of crystal lattices of carbon dioxide and iodine.

Teacher's explanation.

Molecular crystal lattice

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 also 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, a low melting point, are volatile, and are capable of sublimation.

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 the experiment: sublimation of benzoic acid (video experiment).

Working with a completed table.

Appendix 1. (Slide 17)

Crystal lattices, type of bond and properties of substances

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 Table of 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 they contain from four to eight electrons. These are the elements IY A, Y A, YI A, YII A, YIII A and boron.

Teacher: Let's find non-metal elements that have 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 for boron), as well as tin and lead, and all elements of secondary subgroups in a simple substance, the type of lattice is metal.

For the nonmetal elements IY A and boron in a simple substance, the crystal lattice is atomic; and the elements Y A, YI A, YII A, YIII 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 the following conclusion:

There is the following pattern: if the structure of substances is known, then their properties can be predicted, or vice versa: if the properties of substances are known, then the structure can be determined. (Slide 18).

Teacher: Look carefully at the table. What other classification of substances can you suggest?

If the students find it difficult, the teacher explains that substances can be divided into substances of molecular and non-molecular structure. (Slide 19).

Substances with a molecular structure are made up of molecules.

Substances of non-molecular structure consist of atoms and ions.

Teacher: Today we will get acquainted with one of the basic laws of chemistry. This is the law of constancy of composition, which was discovered by the French chemist J.L. Proust. The law is valid only for substances of molecular structure. Currently, the law reads like this: “Molecular chemical compounds, regardless of the method of their preparation, have a constant composition and properties.” But for substances with a non-molecular structure this law is not always true.

Theoretical and practical significance The law is that on its basis the composition of substances can be expressed using chemical formulas (for many substances of non-molecular structure chemical formula shows the composition of not a really existing, but a conditional molecule).

Conclusion: The chemical formula of a substance contains a lot of information.(Slide 21)

For example, SO 3:

1. The specific substance is sulfur dioxide, or sulfur oxide (YI).

2.Type of substance - complex; class - oxide.

3. Qualitative composition - consists of two elements: sulfur and oxygen.

4. Quantitative composition- the molecule consists of 1 sulfur atom and 3 oxygen atoms.

5.Relative molecular mass- M r (SO 3) = 32 + 3 * 16 = 80.

6. Molar mass- M(SO 3) = 80 g/mol.

7. Lots of other information.

Consolidation and application of acquired knowledge

(Slide 22, 23).

Tic-tac-toe game: cross out substances that have the same crystal lattice vertically, horizontally, and diagonally.

Reflection.

The teacher asks the question: “Guys, what new did you learn in class?”

Summing up the lesson

Teacher: Guys, let's summarize the main results of our lesson - answer the questions.

1. What classifications of substances did you learn?

2. How do you understand the term crystal lattice?

3. What types of crystal lattices do you now know?

4. What regularities in the structure and properties of substances did you learn about?

5. In what state of aggregation Do substances have crystal lattices?

6. What basic law of chemistry did you learn in class?

Homework: §22, notes.

1. Make up the formulas of the substances: calcium chloride, silicon oxide (IY), nitrogen, hydrogen sulfide.

Determine the type of crystal lattice and try to predict what the melting points of these substances should be.

2. Creative task -> make up questions for the paragraph.

The teacher thanks you for the lesson. Gives marks to students.

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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Matter, as you know, can exist in three states of aggregation: gaseous, liquid and solid (Fig. 70). For example, oxygen, which under normal conditions is a gas, at a temperature of -194 ° C 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.
Physical states of water

Solids are divided into crystalline and amorphous.

Amorphous substances do not have a clear melting point - when heated, they gradually soften and turn into a fluid state. Amorphous substances include most plastics (for example, polyethylene), wax, chocolate, plasticine, various resins and chewing gums (Fig. 71).

Rice. 71.
Amorphous substances and materials

Crystalline substances are characterized by the correct arrangement of their constituent particles at strictly defined points in space. When these points are connected by straight lines, a spatial framework is formed, called a crystal lattice. The points at which crystal particles are located are called lattice nodes.

The nodes of an imaginary crystal lattice may contain monatomic ions, atoms, and molecules. These particles perform oscillatory movements. With increasing temperature, the range of these oscillations increases, which, as a rule, leads to thermal expansion of bodies.

Depending on the type of particles located at the nodes of the crystal lattice and the nature of the connection between them, four types of crystal lattices are distinguished: ionic, atomic, molecular and metallic (Table 6).

Table 6
Position of elements in the Periodic Table of D. I. Mendeleev and types of crystal lattices of their simple substances

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

Ionic lattices are called crystal lattices whose nodes contain ions. They are formed by substances with ionic bonds, which can bind both simple ions Na +, Cl -, and complex ions, OH -. Consequently, ionic crystal lattices have salts, bases (alkalis), and some oxides. For example, a sodium chloride crystal is built from alternating positive Na + and negative Cl - ions, forming a cube-shaped lattice (Fig. 72). The bonds between ions in such a crystal are very strong. Therefore, substances with an ionic lattice have relatively high hardness and strength, they are refractory and nonvolatile.

Rice. 72.
Ionic crystal lattice (sodium chloride)

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

Rice. 73.
Atomic crystal lattice (diamond)

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

Rice. 74.
Two imperial crowns with diamonds:
a - crown British Empire; b - Great Imperial Crown of the Russian Empire

Substances with an atomic crystal lattice include crystalline boron, silicon and germanium, as well as complex substances, for example, silica, quartz, sand, rock crystal, which include silicon (IV) oxide SiO 2 (Fig. 75).

Rice. 75.
Atomic crystal lattice (silicon (IV) oxide)

Most substances with an atomic crystal lattice have very high melting points (for example, for diamond it is over 3500 °C, for silicon - 1415 °C, for silica - 1728 °C), they are strong and hard, practically insoluble.

Molecular are crystal lattices in which molecules are located at the nodes. The chemical bonds in these molecules can be both covalent polar (hydrogen chloride HCl, water H20) and covalent nonpolar (nitrogen N2, ozone 03). Despite the fact that the atoms inside the molecules are connected by very strong covalent bonds, weak intermolecular forces of attraction act between the molecules themselves. Therefore, substances with molecular crystal lattices have low hardness, low temperatures melting, volatile.

Examples of substances with molecular crystal lattices are solid water - ice, solid carbon monoxide (IV) C) 2 - “dry ice” (Fig. 76), solid hydrogen chloride HCl and hydrogen sulfide H 2 S, solid simple substances formed by mono- (noble gases: helium, neon, argon, krypton), two- (hydrogen H 2, oxygen O 2, chlorine Cl 2, nitrogen N 2, iodine 1 2), three- (ozone O 3), four- (white phosphorus P 4 ), eight-atomic (sulfur S 7) molecules. Most solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).

Rice. 76.
Molecular crystal lattice (carbon dioxide)

Substances with a metallic bond have metallic crystal lattices (Fig. 77). At the sites of such lattices there are atoms and ions (either atoms or ions, into which metal atoms easily turn, giving up their outer electrons for common use). This internal structure metals determines their characteristic physical properties: malleability, ductility, electrical and thermal conductivity, metallic luster.

Rice. 77.
Metal crystal lattice (iron)

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

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

Build a model of one of the crystal lattices.

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

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

Key words and phrases

1. Solid, liquid and gaseous states of matter.
2. Solids: amorphous and crystalline.
3. Crystal lattices: ionic, atomic, molecular and metallic.
4. Physical properties of substances with different types of crystal lattices.
5. Law of constancy of composition.

Work with computer

1. Refer to the electronic application. Study the lesson material and complete the assigned tasks.
2. Find email addresses on the Internet that can serve as additional sources that reveal the content of keywords and phrases in the paragraph. Offer your help to the teacher in preparing a new lesson - make a report on the key words and phrases of the next paragraph.

Questions and tasks

1. What state of aggregation will oxygen be in at -205 °C?
2. Remember the work of A. Belyaev “The Air Seller” and characterize the properties of solid oxygen using its description given in the book.
3. What type of substances (crystalline or amorphous) are plastics? What properties of plastics underlie their industrial applications?
4. What type of diamond crystal lattice is it? List the physical properties characteristic of diamond.
5. What type of iodine crystal lattice is it? List the physical properties characteristic of iodine.
6. Why does the melting point of metals vary over a very wide range? To prepare an answer to this question, use additional literature.
7. Why does a silicon product break into pieces upon impact, while a lead product only flattens out? In which of these cases does the chemical bond break down and in which does it not? Why?

There are two types of solids in nature, which differ markedly in their properties. These are amorphous and crystalline bodies. And amorphous bodies do not have an exact melting point; during heating, they gradually soften and then pass into a fluid state. An example of such substances is resin or ordinary plasticine. But the situation is completely different with crystalline substances. They remain in a solid state until a certain temperature, and only after reaching it do these substances melt.

It's all about the structure of such substances. In crystalline solids, the particles of which they are composed are located at certain points. And if you connect them with straight lines, you get some kind of imaginary frame, which is called a crystal lattice. And the types of crystal lattices can be very different. And according to the type of particles from which they are “constructed,” lattices are divided into four types. These are ionic, atomic, molecular and

And at the nodes, accordingly, ions are located, and there is an ionic bond between them. can be either simple (Cl-, Na+) or complex (OH-, SO2-). And these types of crystal lattices may contain some metal hydroxides and oxides, salts and other similar substances. Take, for example, ordinary sodium chloride. It alternates negative ions chlorine and positive sodium ions, which form a cubic crystal lattice. Ionic bonds in such a lattice are very stable and substances “built” according to this principle have fairly high strength and hardness.

There are also types of crystal lattices called atomic ones. Here, the nodes contain atoms between which there is a strong covalent bond. Atomic lattice do not have very many substances. These include diamond, as well as crystalline germanium, silicon and boron. There are also some complex substances that contain and have, accordingly, an atomic crystal lattice. These are rock crystal and silica. And in most cases, such substances are very strong, hard and refractory. They are also practically insoluble.

And molecular types of crystal lattices have the most different substances. These include frozen water, that is, ordinary ice, “dry ice” - solidified carbon monoxide, as well as solid hydrogen sulfide and hydrogen chloride. Molecular lattices also contain many solid organic compounds. These include sugar, glucose, naphthalene and other similar substances. And the molecules located at the nodes of such a lattice are connected to each other by polar and non-polar chemical bonds. And despite the fact that inside the molecules there are strong covalent bonds between atoms, these molecules themselves are held in the lattice due to very weak intermolecular bonds. Therefore, such substances are quite volatile, melt easily and do not have great hardness.

Well, metals have the most different types crystal lattices. And their nodes can contain both atoms and ions. In this case, atoms can easily turn into ions, giving up their electrons for “common use.” In the same way, ions, having “captured” a free electron, can become atoms. And this lattice determines such properties of metals as plasticity, malleability, thermal and electrical conductivity.

Also, the types of crystal lattices of metals, and other substances, are divided into seven main systems according to the shape of the elementary cells of the lattice. The simplest is the cubic cell. There are also rhombic, tetragonal, hexagonal, rhombohedral, monoclinic and triclinic unit cells that determine the shape of the entire crystal lattice. But in most cases, crystal lattices are more complex than those listed above. This is due to the fact that elementary particles can be located not only in the lattice nodes themselves, but also in its center or on its edges. And among metals, the most common are the following three complex crystal lattices: face-centered cubic, body-centered cubic, and hexagonal close-packed. More physical characteristics metals depend not only on the shape of their crystal lattice, but also on the interatomic distance and other parameters.

Solids usually have a crystalline structure. It is characterized by the correct arrangement of particles at strictly defined points in space. When these points are mentally connected by intersecting straight lines, a spatial frame is formed, which is called crystal lattice.

The points at which particles are located are called crystal lattice nodes. The nodes of an imaginary lattice may contain ions, atoms or molecules. They make oscillatory movements. With increasing temperature, the amplitude of oscillations increases, which manifests itself in thermal expansion tel.

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 most dense packing if the ions are represented as spheres located in the crystal. Very often, crystal lattices are depicted as shown in Fig., where only the relative positions of the particles are indicated, but not their sizes.

The number of nearest neighboring particles closely adjacent to a given particle in a crystal or in an individual 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. There is none of them. The entire crystal should be considered as a giant macromolecule consisting of an equal number of Na + and Cl - ions, Na n Cl n, where n is a large number. The bonds between ions in such a crystal are very strong. Therefore, substances with an ionic lattice have a relatively high hardness. They are refractory and low-flying.

Melting of ionic crystals leads to disruption 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 generally dissolve easily in liquids consisting of polar molecules, such as water.

Crystal lattices, in the nodes of which there are individual atoms, are called atomic. The atoms in such lattices are connected to each other by strong covalent bonds. An example is diamond, one of the modifications of carbon. Diamond is made up of carbon atoms, each of which is bonded to four neighboring atoms. Coordination number of carbon in diamond is 4 . In the diamond lattice, as in the sodium chloride lattice, there are no molecules. The entire crystal should be considered as a giant molecule. The atomic crystal lattice is characteristic of solid boron, silicon, germanium and compounds of some elements with carbon and silicon.

Crystal lattices consisting of molecules (polar and non-polar) are called molecular.

Molecules in such lattices are connected to each other by relatively weak intermolecular forces. Therefore, substances with molecular lattice They have low hardness and low melting points, are insoluble or slightly soluble in water, and 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.