Molecular and non-molecular structure of substances. Structure of matter

It is not individual atoms or molecules that enter into chemical interactions, but substances. Substances are classified according to the type of bond molecular And non-molecular structure. Substances made up of molecules are called molecular substances. The bonds between molecules in such substances are very weak, much weaker than between atoms inside the molecule, and even at relatively low temperatures they break - the substance turns into a liquid and then into a gas (sublimation of iodine). The melting and boiling points of substances consisting of molecules increase with increasing molecular weight. TO molecular substances include substances with an atomic structure (C, Si, Li, Na, K, Cu, Fe, W), among them there are metals and non-metals. To substances non-molecular structure include ionic compounds. Most compounds of metals with non-metals have this structure: all salts (NaCl, K 2 SO 4), some hydrides (LiH) and oxides (CaO, MgO, FeO), bases (NaOH, KOH). Ionic (non-molecular) substances have high temperatures melting and boiling.

Solids: amorphous and crystalline

Solids are divided into crystalline and amorphous.

Amorphous substances they do not have a clear melting point - when heated, they gradually soften and turn into a fluid state. For example, plasticine and various resins are in an amorphous state.

Crystalline substances are characterized correct location those 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 formed, called a crystal lattice. The points at which crystal particles are located are called lattice nodes. 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.

Crystal lattices are called ionic, at the nodes of which there are ions. They are formed by substances with ionic bonds, which can bind both simple ions Na+, Cl -, and complex SO 4 2-, OH -. Consequently, salts and some oxides and hydroxides of metals have ionic crystal lattices. For example, a sodium chloride crystal is built from alternating positive Na + and negative Cl - ions, forming a cube-shaped lattice. The bonds between ions in such a crystal are very stable. Therefore, substances with an ionic lattice are characterized by relatively high hardness and strength, they are refractory and non-volatile.

Crystalline lattice - a) and amorphous lattice - b).

Atomic crystal lattices

Atomic are called crystal lattices, in the nodes of which there are individual atoms. In such lattices the atoms are connected to each other very strong covalent bonds. An example of substances with this type of crystal lattices is diamond, one of the allotropic modifications of carbon. Most substances with an atomic crystal lattice have very high melting points (for example, for diamond it is over 3500 ° C), they are strong and hard, and practically insoluble.

Molecular crystal lattices

Molecular called crystal lattices, in the nodes of which molecules are located. Chemical bonds in these molecules can be both polar (HCl, H 2 O) and non-polar (N 2, O 2). Despite the fact that the atoms inside the molecules are connected by very strong covalent bonds, weak forces of intermolecular attraction act between the molecules themselves. Therefore, substances with molecular crystal lattices have low hardness, low melting points, and are volatile. Most solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).

Metal crystal lattices

Substances with metal bond have metal crystal lattices. At the nodes of such lattices there are atoms and ions(either atoms or ions, into which metal atoms easily transform, giving up their outer electrons “to common use"). This internal structure metals determines their characteristic physical properties: malleability, plasticity, electrical and thermal conductivity, characteristic metallic luster.

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Lesson type: Combined.

The main goal of the lesson: To give students specific ideas about amorphous and crystalline substances, types of crystal lattices, to 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. Under 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 and solid state by lowering the temperature: for example, oxygen, which at a temperature (-194 0 C) turns into a blue liquid, and at a temperature (-218.8 0 C) solidifies 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 by the correct arrangement of the 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 crystalline substances upon impact, they split in certain planes, but 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. Melts conduct them electricity(Why?), 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 melting points (diamond has over 3500 0 C), are strong and hard, non-volatile, and 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 general physical properties are characteristic of 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: Substances are fragile, have low hardness, low temperature melting, volatile, 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 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 IY A, Y A, YI A, YII A, YIII 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 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, based on it, the composition of substances can be expressed using chemical formulas (for many substances of non-molecular structure, the chemical formula shows the composition of not a real 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 weight - 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, 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 know, all material substances can exist in three basic states: liquid, solid, and gaseous. True, there is also a state of plasma, which scientists consider no less than the fourth state of matter, but our article is not about plasma. The solid state of a substance is therefore solid because it has a special crystalline structure, the particles of which are in a certain and clearly defined order, thus creating a crystal lattice. The structure of the crystal lattice consists of repeating identical elementary cells: atoms, molecules, ions, and other elementary particles connected by various nodes.

Types of crystal lattices

Depending on the particles of the crystal lattice, there are fourteen types of it, here are the most popular of them:

• Ionic crystal lattice.
• Atomic crystal lattice.
• Molecular crystal lattice.
• crystal cell.

Ionic crystal lattice

The main feature of the structure of the crystal lattice of ions is the opposite electrical charges of the ions themselves, as a result of which an electromagnetic field is formed, which determines the properties of substances having an ionic crystal lattice. And these are refractoriness, hardness, density and the ability to conduct electric current. A typical example of an ionic crystal lattice is table salt.

Atomic crystal lattice

Substances with an atomic crystal lattice, as a rule, have strong atoms in their nodes. A covalent bond occurs when two identical atoms share fraternal electrons with each other, thus forming a common pair of electrons for neighboring atoms. Because of this, covalent bonds bind atoms tightly and evenly in a strict order - perhaps this is the most characteristic structure of the atomic crystal lattice. Chemical elements with similar bonds can boast of their hardness and high melting point. Chemical elements such as diamond, silicon, germanium, and boron have an atomic crystal lattice.

Molecular crystal lattice

The molecular type of crystal lattice is characterized by the presence of stable and closely packed molecules. They are located at the nodes of the crystal lattice. In these nodes they are held by van der Waltz forces, which are ten times weaker than the forces of ionic interaction. A striking example of a molecular crystal lattice is ice - a solid substance, which, however, has the property of turning into a liquid - the bonds between the molecules of the crystal lattice are very weak.

Metal crystal lattice

The type of bond of a metal crystal lattice is more flexible and ductile than the ionic one, although in appearance they are very similar. Distinctive feature it is the presence of positively charged cations (metal ions) at lattice sites. Between the nodes live electrons that participate in the creation electric field, these electrons are also called electric gas. The presence of such a metal crystal lattice structure explains its properties: mechanical strength, heat and electrical conductivity, fusibility.

Crystal lattices, video

And in conclusion detailed video explanations about the properties of crystal lattices.

According to Boyle's atomic-molecular theory, all substances consist of molecules that are in constant motion. But is there any specific structure in substances? Or are they simply made up of randomly moving molecules?

In fact, all substances in a solid state have a clear structure. Atoms and molecules move, but the forces of attraction and repulsion between particles are balanced, so atoms and molecules are located at a certain point in space (but continue to make small fluctuations depending on temperature). Such structures are called crystal lattices. The places in which the molecules, ions or atoms themselves are located are called nodes. And the distances between the nodes are called - periods of identity. Depending on the position of particles in space, there are several types:

1. atomic;
2. ionic;
3. molecular;
4. metal.

In liquid and gaseous states, substances do not have a clear lattice; their molecules move chaotically, which is why they have no shape. For example, oxygen, when in a gaseous state, is a colorless, odorless gas; in a liquid state (at -194 degrees) it is a bluish solution. When the temperature drops to -219 degrees, oxygen turns into a solid state and becomes red. lattice, while it turns into a snow-like mass of blue color.

Interestingly, amorphous substances do not have a clear structure, which is why they do not have strict temperature melting and boiling. When heated, resin and plasticine gradually soften and become liquid; they do not have a clear transition phase.

Atomic crystal lattice

The nodes contain atoms, as the name suggests. These substances are very strong and durable, since a covalent bond is formed between the particles. Neighboring atoms share a pair of electrons with each other (or rather, their electron clouds are layered on top of each other), and therefore they are very well connected to each other. The most obvious example is diamond, which has the greatest hardness on the Mohs scale. Interestingly, diamond, like graphite, consists of carbohydrates. Graphite is a very brittle substance (Mohs hardness 1), which is a clear example how much depends on the species.

Atomic region lattice poorly distributed in nature, it includes: quartz, boron, sand, silicon, silicon oxide (IV), germanium, rock crystal. These substances are characterized by a high melting point, strength, and these compounds are very hard and insoluble in water. Due to the very strong bonds between atoms, these chemical compounds hardly interact with others and conduct current very poorly.

Ionic crystal lattice

In this type, ions are located at each node. Accordingly, this type is characteristic of substances with an ionic bond, for example: potassium chloride, calcium sulfate, copper chloride, silver phosphate, copper hydroxide, and so on. Substances with such a particle connection scheme include;

• salt;
• metal hydroxides;
• metal oxides.

Sodium chloride has alternating positive (Na +) and negative (Cl -) ions. One chlorine ion located in a node attracts two sodium ions (due to electromagnetic field), which are located in neighboring nodes. Thus, a cube is formed in which the particles are interconnected.

The ionic lattice is characterized by strength, refractoriness, stability, hardness and non-volatility. Some substances can conduct electricity.

Molecular crystal lattice

The nodes of this structure contain molecules that are tightly packed together. Such substances are characterized by covalent polar and nonpolar bonds. It is interesting that, regardless of the covalent bond, there is a very weak attraction between the particles (due to weak van der Waals forces). That is why such substances are very fragile, have low boiling and melting points, and are also volatile. These substances include: water, organic substances (sugar, naphthalene), carbon monoxide (IV), hydrogen sulfide, noble gases, two- (hydrogen, oxygen, chlorine, nitrogen, iodine), three- (ozone), four- (phosphorus ), eight-atomic (sulfur) substances, and so on.

One of distinctive features — this is that the structural and spatial model is preserved in all phases (both solid, liquid and gaseous).

Metal crystal lattice

Due to the presence of ions at the nodes, the metal lattice may appear to be similar to an ionic lattice. In fact, these are two completely different models, with different properties.

Metal is much more flexible and ductile than ionic, it is characterized by strength, high electrical and thermal conductivity, these substances melt well and conduct electric current well. This is explained by the fact that the nodes contain positively charged metal ions (cations), which can move throughout the structure, thereby ensuring the flow of electrons. Particles move chaotically around their node (they do not have enough energy to go beyond), but as soon as electric field, electrons form a flow and rush from the positive to the negative region.

The metal crystal lattice is characteristic of metals, for example: lead, sodium, potassium, calcium, silver, iron, zinc, platinum and so on. Among other things, it is divided into several types of packaging: hexagonal, body-centered (least dense) and face-centered. The first package is typical for zinc, cobalt, magnesium, the second for barium, iron, sodium, the third for copper, aluminum and calcium.

Thus, depending on the grating type many properties depend, as well as the structure of the substance. Knowing the type, you can predict, for example, what the refractoriness or strength of an object will be.

Most solids have a crystalline structure. Crystal cell 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 heat of solution and heat of fusion, and electrical conductivity.

An important characteristic of a 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. These are a large number of 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 lattices with substances that form hydrogen bonds (H 2 O, NH 3) have the highest energy.

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 different elements connected to each other 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, as well as crystals of complex substances such as boron nitride, aluminum nitride, quartz, and 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, 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 fragile. 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 solid 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

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