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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 blue crystals. 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 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).
Ionic crystal lattices
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.
Atomic crystal lattices
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 located 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.
Metal crystal lattices
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.
Molecular crystal lattices
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
| Grille type | Types of particles at lattice sites |
Type of connection 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 nonpolar - 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 (IY)-SiO 2 |
Very hard, very refractory, durable, non-volatile, insoluble in water |
| Molecular | Molecules | Between molecules there are weak forces of intermolecular attraction, but inside the molecules there is a strong covalent bond | Solids under special conditions that under normal conditions are gases or liquids (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 of different strengths | Metals and alloys | Malleable, shiny, ductile, thermally and electrically conductive |
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.
Law of Constancy of Composition
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.
The theoretical and practical significance of the law is that on its basis 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.
Page 1
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, 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.
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.
What exists in nature is formed by a large number of identical particles that are connected to each other. All substances exist in three states of aggregation: gaseous, liquid and solid. When thermal movement is difficult (at low temperatures), as well as in solids, the particles are strictly oriented in space, which is manifested in their precise structural organization.
The crystal lattice of a substance is a structure with a geometrically ordered arrangement of particles (atoms, molecules or ions) at certain points in space. In various lattices, a distinction is made between the internodal space and the nodes themselves - the points at which the particles themselves are located.
There are four types of crystal lattice: metallic, molecular, atomic, ionic. The types of lattices are determined in accordance with the type of particles located at their nodes, as well as the nature of the connections between them.
A crystal lattice is called molecular if molecules are located at its nodes. They are connected by intermolecular relatively weak forces, called van der Waals forces, but the atoms themselves inside the molecule are connected by a significantly stronger or non-polar force). The molecular crystal lattice is characteristic of chlorine, solid hydrogen, and other substances that are gaseous at ordinary temperatures.
The crystals that form the noble gases also have molecular lattices consisting of monatomic molecules. Most organic solids have this structure. The number of which has a molecular structure is very small. These are, for example, solid hydrogen halides, natural sulfur, ice, simple solids and some others.
When heated, relatively weak intermolecular bonds are destroyed quite easily, therefore substances with such lattices have very low melting points and low hardness, they are insoluble or slightly soluble in water, their solutions practically do not conduct electric current, and are characterized by significant volatility. The minimum boiling and melting points are for substances made from non-polar molecules.
A crystal lattice is called metallic, the nodes of which are formed by atoms and positive ions (cations) of the metal with free valence electrons (detached from the atoms during the formation of ions), randomly moving in the volume of the crystal. However, these electrons are essentially semi-free, since they can move freely only within the framework that is limited by a given crystal lattice.
Electrostatic electrons and positive metal ions are mutually attracted, which explains the stability of the metal crystal lattice. The collection of free moving electrons is called electron gas - it provides good electrical and When an electrical voltage appears, electrons rush to the positive particle, participating in the creation of electric current and interacting with ions.
The metallic crystal lattice is characteristic mainly of elemental metals, as well as of compounds of different metals with each other. The main properties that are inherent in metal crystals (mechanical strength, volatility, fluctuate quite strongly. However, such physical properties as plasticity, malleability, high electrical and thermal conductivity, and a characteristic metallic luster are characteristic only exclusively of crystals with a metal lattice.
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 alternate, between which electrostatic forces act. Ionic crystals form compounds with ionic bonds, for example, sodium chloride NaCl, potassium fluoride and KF, etc. Ionic compounds may also include complex ions, for example, NO 3 -, SO 4 2 -.
Ionic crystals are also a giant molecule in which each ion is significantly influenced by all other ions.
The energy of the ionic crystal lattice can reach significant values. So, E (NaCl) = 770 kJ/mol, and E (BeO) = 4530 kJ/mol.
Ionic crystals have high melting and boiling points and high strength, but are brittle. Many of them conduct electricity poorly at room temperature (about twenty orders of magnitude lower than 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 by high values of electrical conductivity and thermal conductivity.
In terms of crystal lattice energy, metals occupy an intermediate position between molecular and covalent crystals. The energy of the crystal lattice is:
Thus, the physical properties of solids depend significantly on the type of chemical bond and structure.
Structure and properties of solids
| Characteristics | Crystals | |||
| Metal | Ionic | Molecular | Atomic | |
| Examples | K, Al, Cr, Fe | NaCl, KNO3 | I 2, naphthalene | diamond, quartz |
| Structural particles | Positive ions and mobile electrons | Cations and anions | Molecules | Atoms |
| Type of chemical bond | Metal | Ionic | In molecules – covalent; between molecules - van der Waals forces and hydrogen bonds | Between atoms - covalent |
| t melting | High | High | Low | Very high |
| boiling point | High | High | Low | Very high |
| Mechanical properties | Hard, malleable, viscous | Hard, brittle | Soft | Very hard |
| Electrical conductivity | Good guides | In solid form - dielectrics; in a melt or solution - conductors | Dielectrics | Dielectrics (except graphite) |
| Solubility | ||||
| in water | Insoluble | Soluble | Insoluble | Insoluble |
| in non-polar solvents | Insoluble | Insoluble | Soluble | Insoluble |
(All definitions, formulas, graphs and equations of reactions are given on record.)
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:
- atomic;
- ionic;
- molecular;
- 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 melting and boiling points. 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 of how much depends on the type.
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 the electromagnetic field) that 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 the distinguishing features is 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. The particles move chaotically around their node (they do not have enough energy to go beyond), but as soon as an electric field appears, electrons form a stream 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.