In accordance with the basic principle that matter always seeks to occupy the energetically most favorable condition, individual atoms have a more or less pronounced tendency to create an atomic connection. The difference of the energy of a separate EA atom and an atom in a solid compound, in particular in a crystal, Ek is called the EV binding energy. This bond energy EV \u003d EA-EK is equal to the energy spent on the release of a separate atom from its connection. It depends on the corresponding type of communication, which creates an atomic connection.
In the forces providing the grip of the crystal, we are talking about attraction between negatively charged electrons and positively charged atomic nuclei. These attraction forces are formed from the desire of atoms to achieve saturation of quantum states in the corresponding outer shell, i.e. Adopt inert gas configuration. On the 2nd, 3rd, 4th shell, this happens in the case of fully occupied S- and P-states (S2 and P6), i.e. When this, respectively, the outer shell with eight electrons.
Attraction forces are opposed to the repulsion force between the same name of the chores and between electrons. From the equilibrium of the attraction and repulsion forces forces, the distance between atoms in a crystalline compound, determined by the quantum states of external electrons and the type of communication (Fig. 5.6.1). For the distance R0, the strength of attraction and repulsion is compensated (equalized). The crystalline compound is in equilibrium.

Thus, it can be understood that the structure of external electronic shells leads to various types of communication between individual atoms. The type of communication is determined by the characteristic properties of the atomic connection. If it is necessary to give the greatest attention of the metallic connection, then other types of solid bodies should be considered to understand the structure and properties of solids. Depending on the magnitude of the binding energy, the following types differ (Fig. 5.6.2):
1. The connection of Van der Waals (see Fig. 5.6.2, a).
This type of communication is available in solid inert gases and molecular crystals. It has a very low communication energy. Since the inert gases have complete (occupied) quantum states on the outer shell, then the desire of such atoms to unite into a strong compound can be explained by the fact that the distribution of charges is not symmetric spherically, but has a di-full moment. Positive and negative poles cause weak compounds (clutches) of these solids, which crystallized with the tight packaging of the balls-atoms.
2. Metal communication (See Fig. 5.6.2, b).
In metals there is a relatively thin filled outer electronic shell. External electrons of atoms are given and no longer belong to certain atoms. In some metals, for example, Fe and B, on nearby internal electron shells, not fully occupied quantum states contribute to communication. Ion Metal Frames "float" in an electronic gas that acts as a "hitch". Thanks to freely moving electrons, good electrical conductivity is created. Since all atoms in metals occupy equivalent positions, at the action of external forces, atoms can be shifted relative to each other, and they always find equal places in the neighborhood. This can explain the good plasticity of metals. At the same time, from the nature of communication there is a tendency of metals to the tight packaging of the balls-atoms.
3. Homeopolar (covalent) communication (see Fig. 5.6.2, B).
Here we are talking about valence. With the help of directional valence forces, homogeneous atoms are connected. Communication energy at the same time is relatively large. In the desire for a filled outer shell, the atoms are connected so that the missing electrons are replaced in such a way that two or more electrons are treated simultaneously to two or more atoms. Chlorine with seven electrons, for example, has an unoccupied energy condition in the outer shell. Due to the compound of two chlorine atoms, these two electrons are divided in such a way that in the CL2 molecule for each atom there is a fully occupied shell. Because of this, energy is reduced in the molecule of a separate atom.
If there are two electrons for complete substitution of the energy state on the outer shell, the covalent bond is stable, for example, Sb3 antimony. In carbon on the outer shell there are no four electrons, so that carbon atom with four closest neighbors divides missing electrons. Thus, in diamond, the configuration of five atoms is stable. The number of closest neighbors, i.e. The coordination number is calculated in this way from 8-n, and n is the number of electrons in the outer shell. Thus, a covalent bond is possible only at elements with N ≤ 4. With N ≥ 4, the number of electrons for this type of clutch is not enough. Covalent ties crystals Very solid (diamond) and detect in pure form Very minor conductivity.
4. Heteropolar (ionic) communication (see Fig. 5.6.2, d).

This type of communication has very high energy. According to this type, elements with almost completely engaged external electronic shells with elements with almost unoccupied external shells are connected. To form closed shells, one element gives an electron, another element takes them.
So, the NaCl crystal is formed due to the fact that Na gives its electron on the outer shell, and CL, which does not have an electron, accepts it. Due to this, Na + with a positive extension of charge becomes a cation, CL- with a negative charge - anion. Communication through the electrostatic interaction of oppositely charged ions. In an ion crystal, the ions are located in such a way that the Coulomb attraction of variance charges is stronger than the Coulomb repulsion of the same ions. Characteristic crystal structures for ionic crystals are the structure of sodium chloride and cesium chloride. Since the deformation of communication should be impaired, these crystals, like covalent, are solid and fragile. Solid bodies with ion bonds have electrolytic conductivity.
In metals, along with metallic clutch, ionic and covalent bond. These types of communication are detected mainly in the intermetallic phases. At the same time, these types of communication in most cases are found not a pure state, but in mixed forms. Intermetallic; The phases as opposed to purely metallic are very hard, fragile and retain their strength properties to high temperatures. Thus, the intermetallic phases are suitable in order to make metals with solid, wear and heat-resistant.
Important forms of intermetallic phases are carbides.
In addition to the considered types of communication, you need to call another hydrogen bridge. This connection is mainly an ionic nature. The hydrogen atom loses its electron and, precipitating, creates a bridge between strongly negative atoms, such as F, N and O.

§one. As electrons "kisov" covalent bond

Molecules consist of atoms interconnected.
But as connected - adhesive, glued, composed by one chain? And who is the mechanic, a joiner or a blacksmith, who connects the atoms together?
You already know that in antiquity it was considered in the order of things that atoms are combined with hooks. From here not far to buttons with loops.
If you drop the jokes, we will have to admit that the question is not easy: because the shell of each of the atoms connected in the molecule consists of electrons charged the same on the sign, so when trying to bring the electronic clouds to bring the electronic clouds, strong repulsion will inevitably occur.
But atoms are still connect! Moreover, with the help of those the most electrons that seem to be counteracting the connection.

That's how it happens ...
Recall that the electrons in the atom we denoted in different ways - an arrow pointing upwards and an arrow directed down:

And ↓

and located between the cores of the two atoms. Both positively charged nuclei of atoms will be attracted to a negative electronic pair, and therefore, both to each other:

So it is formed from two separate atoms the simplest dimensional molecule. For example, from two atoms hydrogen N. It turns out molecule H 2.:

Anything remains: to understand why this suddenly two electrons swung to unite in a pair?

Ancient Greek philosophers had a unambiguous answer to this question. They believed that, the events in the world of atoms rule, like people, two feelings - love and enough.
So mutual repulsion is enough, and the connection of two atoms is friendship, love And, in the end, happy marriage.

Naive representations of antiquity Nowadays, it is necessary to support any real, physical explanations. But we will not assume that two electrons are two shooters - cling to each other with their plumage? The point is completely different!

Each electron, in addition to the electric charge, has a magnetic moment and behaves like microscopic magnet. Two electrons with multidirectional arrows is two such micromagnet With oppositely oriented poles. Here they are attracted to each other:

Anyway, the pair of electrons is formed. But that this happens, it is necessary that the atoms get to each other, and their electronic clouds are partially combined. Chemists call this situation in the atomic "economy" overlapping atomic orbitals.

Take the same example of the formation of hydrogen molecule from atoms. Two spherical (spherical) orbital, two electronic clouds overlap and enter one to another, like this:

At the same time it is formed covalent communication.

Covalent is called such a chemical bond, which is formed using a pair of electrons.

If you transfer our picture to the language of quantum cells, it will look like this:

Chemists say that chemical bond in this case was formed by exchange(otherwise - by "equivalent") mechanism".

Exactly the same hydrogen molecule may be formed differently, if you interact with each other cation hydrogen N. + (He has no electron, but only empty atomic orbital) I. anion hydrogen N. - which has a pair of electrons:

H + + H - \u003d H 2

On the energy diagram it looks like this.

Chemistry is amazing and, confess, tangled science. For some reason, it is associated with bright experiments, multi-colored test tubes, dense steam clouds. But few people think about whether this "magic" comes from. In fact, no reaction passes without the formation of compounds between the atoms of the reagents. Moreover, these "jumpers" are sometimes found in simple elements. They affect the ability of substances to enter into the reaction and explain some of their physical properties.

What kind of types chemical ties And how do they affect the connections?

Theory

You need to start with the simplest. Chemical bond is the interaction in which the atoms of substances are connected and form more complex substances. It is mistaken to believe that this is typical of only compounds like salts, acids and bases - even simple substances that are molecules of two atoms, have these "jumpers", if so it is possible to change the connection. By the way, it is important to remember that only atoms having different charges can unite (these are the foundations of physics: the same charged particles are repelled, and the opposite - are attracted), so that complex substances There is always a cation (ion with a positive charge) and anion (negative particle), and the connection itself will always be neutral.

Now let's try to figure out how the formation of a chemical connection occurs.

Education mechanism

Any substance has a certain amount of electrons distributed by energy layers. The most vulnerable is the outer layer, on which the smallest number of these particles is usually located. You can learn their number by looking at the number of the group (line with numbers from one to eight at the top of the Mendeleev table), in which the chemical element is located, and the amount of energy layers is equal to the period number (from one to seven, the vertical string to the left of the elements).

Ideally, there are eight electrons on the external energy layer. If they are missing, the atom tries to drag them in another particle. It is in the process of selecting the electrons necessary to complete the external energy layer of electrons formed by chemical connections of substances. Their number may vary and depends on the number of valence, or unpaired, particles (to find out how many of them in the atom, it is necessary to make it an electronic formula). The number of electrons that do not have a couple will be equal to the number of ties formed.

A little more about types

Types of chemical bonds formed during reactions or simply in a molecule of some substance are entirely dependent on the element itself. There are three types of "jumpers" between atoms: ion, metallic and covalent. The latter, in turn, is divided into polar and non-polar.

In order to understand which bonds are associated atoms, use a kind of rule: if elements are in the right and left parts of the table (that is, they are metal and non-metallol, such as NaCl), then their connection is an excellent example of ion connection. Two non-metals form (HCl), and two atoms of a substance, connecting into one molecule, is a covalent non-polar (CL 2, O 2). The above types of chemical bonds are not suitable for substances consisting of metals - it is found exclusively

Covalent interaction

As mentioned earlier, the types of chemical bonds have a certain effect on substances. So, for example, a covalent "jumper" is very unstable, due to which the compounds with it are easily destroyed at the slightest external effect, heating for example. True, concerns it only molecular substances. Those that have nemolecular structure, practically indestructible (the perfect example is a diamond crystal - a compound of carbon atoms).

Let's return to the polar and non-polar with non-polar, everything is simple - the electrons, between which the "jumper" is formed, are at an equal distance from atoms. But in the second case, they are shifted to one of the elements. The winner in the "Treatment" will be the substance, electronegability (the ability to attract electrons) of which is higher. It is determined by special tables, and the greater the difference of this value in two elements, the more polar communication between them. True, the only thing for which the knowledge of the electronegability of the elements can be useful is the definition of the cation (a positive charge - a substance that this value will be less) and anion (negative particle with a better ability to attract electrons).

Ion communication

Not all types of chemical bonds are suitable for the metal and nonmetal. As mentioned above, if the difference in the electronegativity of the elements is huge (namely, it happens when they are located in the opposite parts of the table), it is formed between them ion communication. In this case, the valence electrons move from an atom with less electronegacity to the atom with greater, forming anion and cation. The most striking example of this connection is the compound of halogen and metal, for example AlCl 2 or HF.

Metal communication

Metals are still easier. They are alien to the types of chemical relations, because they have their own. It can be combined as atoms of one substance (Li 2) and different (AlCr 2), in the latter case alloys are formed. If speak about physical properties, Metals combine plasticity and durability in themselves, that is, they are not destroyed at the slightest exposure, but simply change the form.

Intermolecular communication

By the way, chemical bonds in molecules also exist. They are also called intermolecular. The most common type - hydrogen communicationsIn which the hydrogen atom binds the electrons by the element with high electronegathy (in the water molecule, for example).

ATTENTION, only today!

Degree of oxidation

About visuality of conditional charge

Each teacher knows how much means the first year of studying chemistry. Will it be clear, interesting, important in life and when choosing a profession? Much depends on the teacher's skill is available and visually answer the "simple" questions of students.

One of these questions: "Where do the formulas come from?" - requires knowledge of the concept of "oxidation".

The wording of the concept of "degree of oxidation" as "the conditional charge of atoms of chemical elements in a compound calculated on the basis of the assumption that all compounds (and ionic, and covalently polar) consist only of ions" (see: Gabrielyan O.S.Chemistry-8. M.: Drop, 2002,
from. 61) Available to a few students who understand the nature of the formation of a chemical bond between atoms. Most remember this definition is difficult, it needs to sharpen. And for what?

Definition - a step in knowledge and becomes a tool for work when it is not urged, but I remember because it is clear.

At the beginning of the study of the new subject, it is important to clearly illustrate abstract concepts, which are especially many in the course of the chemistry of the 8th grade. It is this approach that I want to offer, and to form the concept of "degree of oxidation" until the study of the types of chemical bonds and as a basis for understanding the mechanism of its education.

From the first lessons, eighth graders learn to apply periodic system Chemical elements as a reference table for compiling the formation of atoms and determine their properties in the number of valence electrons. Starting to the formation of the concept of "degree of oxidation", I spend two lessons.

Lesson 1.
Why Nemmetalov atoms
Are you connected to each other?

Let's be fantasized. How would the world look like, if the atoms were not connected, there would be molecules, crystals and larger formations? The answer is striking: the world would be invisible. The world of physical bodies, animated and inanimate, just no!

Next, we discuss whether all the atoms of chemical elements are connected. Is there any single atoms? It turns out that there are atoms of noble (inert) gases. Compare electronic structure The atoms of noble gases, find out the peculiarity of completed and sustainable external energy levels:

Expression "External Energy Levels Completed and Stable" means that these levels contain the maximum number of electrons (at the Helium Atom - 2 e., at the atoms of other noble gases - 8 e.).

How to explain the stability of an external eight-electron level? In the periodic system, eight groups of elements, it means that the maximum number of valence electrons is eight. The noble gases atoms are single because they have the maximum number of electrons in the external energy level. They do not form any molecules as CL 2 and P 4 nor crystal latticeslike graphite and diamond. Then it can be assumed that the atoms of the remaining chemical elements seek to accept the shell of noble gas - eight electrons in the external energy level - connecting to each other.

We will verify this assumption on the example of the formation of the water molecule (formula H 2 O is known to students, such as the fact that water is the main substance of the planet and life). Why water formula H 2 o?

Using atomic schemes, students are guessing why it is advantageous to compound two atoms H and one atom about in the molecule. As a result of the displacement of single electrons from two hydrogen atoms, eight electrons are placed at an oxygen atom at an oxygen atom. Students offer different methods Mutual arrangement of atoms. We choose a symmetrical option, emphasizing that nature lives according to the laws of beauty and harmony:

The compound of atoms leads to the loss of their electronutrality, although the molecule is generally electronically:

The emerging charge is defined as conditional, because It is "hidden" inside the electrophetral molecule.

We form the concept of "electronegacity": an oxygen atom has a conditional negative charge -2, because He dismissed two electrons from hydrogen atoms. So, oxygen electronegable hydrogen.

We write: electricity (EO) is the property of atoms to shift valence electrons from other atoms. We work with a number of electronegability of non-metals. Using the periodic system, explain the highest electronenence fluorine.

Combining all of the above, we formulate and write down the determination of the degree of oxidation.

The degree of oxidation is a conditional charge of atoms in a compound equal to the number of electrons shifted to atoms with greater electronegitability.

It is possible to explain the term "oxidation" as the return of electrons atoms of the more electronegative element, emphasizing that when the atoms of different non-metals are connected, only the electron displacement to more electrone-negative non-metal. Thus, electronegativity is the property of non-metal atoms, which is reflected in the title "A number of electronegability of non-metals".

According to the law of constancy composition of substances, Opened French scientist Joseph Louis Proust in 1799-1806, each chemically clean substance, regardless of the location and method of receipt, has the same constant composition. So, if there is water on Mars, then it will be the same "Ash-two-O"!

As a fixing of the material, we check the "correctness" of the carbon dioxide formula, to the formula of the formula of the CO 2 molecule:

Atoms with different electronegitility are connected: carbon (EO \u003d 2.5) and oxygen (EO \u003d 3.5). Valence electrons (4 e.) The carbon atom is shifted to two oxygen atoms (2 e. - To one atom about and 2 e.- To another atom about). Consequently, the degree of carbon oxidation is +4, and the degree of oxidation of oxygen -2.

Connecting, the atoms are completed, make their external energy level stable (complement it to 8 e.). That is why the atoms of all elements besides noble gases are connected to each other. The atoms of noble gases are single, their formulas are written by the sign of the chemical element: not, NE, Ar and so on.

The degree of oxidation of the atoms of noble gases, as well as all atoms in the free state, is zero:

This is understandable, because Atoms are electronic.

The degree of oxidation of atoms in molecules of simple substances is also zero:

When connecting atoms of one element, no electron displacement occurs, because Their electronegability is the same.

I use the reception of the paradox: how to complement your external energy level up to eight electrons atoms of non-metals in the composition of dimensional gases molecules, for example, chlorine? Schematically present the question like this:

Shifts of valence electrons ( e.) does not happen, because Electricity of both chlorine atoms are the same.

This question puts students in a dead end.

As a tip, it is proposed to consider a simpler example - the formation of a diatomic hydrogen molecule.

Students quickly recognize: the displacement of the electrons is impossible, atoms can combine their electrons. The scheme of this process is as follows:

Valence electrons become common, connecting atoms into a molecule, while the external energy level of both hydrogen atoms becomes complete.

I propose to portray valence electrons points. Then the total pair of electrons should be placed on the axis of symmetry between atoms, because When connecting atoms of one chemical element of electron displacement does not occur. Consequently, the degree of oxidation of hydrogen atoms in the molecule is zero:

So the basis is laid for studying in the further covalent bond.

We return to the formation of the chlorine ductomic molecule. Some of the students guessed to propose the following scheme of compounds of chlorine atoms in a molecule:

I draw the attention of students that the total pair of electrons connecting the chlorine atoms into the molecule, form only unpaired valence electrons.

So students can do their discoveries, the joy of which not only remember for a long time, but also develops creative abilities, the person in general.

Students have a task: to depict the formation schemes of common electronic pairs in fluorine molecules F 2, HCL chloride, oxygen O 2 and determine the degrees of oxidation in them atoms.

In your homework, you need to move away from the template. So, in the preparation of the formation scheme of the oxygen molecule, students should be depicted not alone, but two common pairs of electrons on the axis of symmetry between atoms:

In the formation scheme of the chloride molecule, show the displacement of the overall pair of electrons to a more electronegative chlorine atom:

In compounding the HCl of the degree of oxidation of atoms: H - +1 and CL - -1.

Thus, determining the degree of oxidation as a conditional charge of atoms in a molecule, equal to the number of electrons shifted to atoms with greater electronegitability, makes it possible not only to formulate this concept clearly and accessible, but also make it the basis for understanding the nature of chemical bond.

Working on the principle of "first to understand, and then remember", applying the reception of the paradox and creating problematic situations in the lessons, you can get not only good learning results, but also to achieve an understanding of even the most complex abstract concepts and definitions.

Lesson 2.
Compound of metals atoms
with non-metals

For checking homework I propose to students compare two versions of a visual image of the compound of atoms into the molecule.

Options for image formation molecules

M o l k u l a f t o r a f 2

Option 1.

Atoms of one chemical element are connected.

Electric monastery atoms is the same.

Displacements of valence electrons does not occur.

How the fluorine Fluent molecule is formed with n o.

Option 2.
Pairing valence electrons of the same atoms

We depict valence electrons of fluorine atoms:

Unpaired the valence electrons of fluorine atoms formed a common pair of electrons depicted in the molecule scheme on the axis of symmetry. Since the shifts of valence electrons does not occur, the degree of oxidation of fluorine atoms in the molecule F 2 is zero.

The result of the compound of fluorine atoms into the molecule with the help of a common pair of electrons was the completed external eight-electron level of both fluorine atoms.

Similarly, the formation of oxygen molecule O 2 is considered.

M o l k u l a k i l o r about d and o 2

Option 1.
Using atoms structure

Option 2.
Fishing of valence electrons of the same atoms

M o l c u l a x l o r o v o d o r o d a HCl

Option 1.
Using atoms structure

A more electronegative chlorine atom has shifted one valence electron from the hydrogen atom. Conditional charges occurred on atoms: the degree of oxidation of the hydrogen atom is +1, the degree of oxidation of the chlorine -1 atom.

As a result of the compound of atoms in the HCl molecule, the hydrogen atom "lost" (according to the scheme) its valence electron, and the chlorine atom completed its external energy level to eight electrons.

Option 2.
Pairing valence electrons different atoms

Unpaired valence electrons of hydrogen and chlorine atoms formed a common pair of electrons shifted to a more electronegative chlorine atom. As a result, conditional charges were formed at the atoms: the degree of oxidation of the hydrogen atom is +1, the degree of oxidation of the chlorine -1 atom.

When connecting atoms into a molecule using a common pair of electrons, their external energy levels become completed. At the hydrogen atom, the external level becomes two-electron, but shifted to a more electronegative chlorine atom, and at the chlorine atom - stable eight-electron.

Let us dwell on the last example - the formation of the HCl molecule. Which scheme is more accurate and why? Students notice a significant difference. The use of atomic circuits during the formation of a HCl molecule involves the displacement of the valence electron from the hydrogen atom to a more electronegative chlorine atom.

I remind you that electronegativity (the property of atoms to shift valence electrons from other atoms) to varying degrees inherent in all elements.

Students come to the conclusion that the use of atomic circuits in the formation of HCl does not make it possible to show the displacement of electrons to a more electronegative element. The image of the valence electrons points more accurately explains the formation of the hydraulic rod molecule. When binding atoms H and CL, a bias is associated (in the diagram - deviation from the symmetry axis) of the valence electron of the hydrogen atom to a more electronegative chlorine atom. As a result, both atoms acquire a certain degree of oxidation. Unpaired valence electrons not only formed a common pair of electrons connected atoms into a molecule, but also completed the external energy levels of both atoms. The formation schemes of the molecules F 2 and 2 of the atoms are also more clear when the valence electrons is drawn by points.

According to the example of the previous lesson with its main question "Where do the formulas come from?" Students are invited to answer the question: "Why does NaCl formula salt?"

About b r a z o in a n and e x l o r and d and n and t p and i naCl

Students make up the following scheme:

I speak: sodium - element Ia subgroup, has one valence electron, therefore, it is a metal; Chlorine - element of VIIA subgroup, has seven valence electrons, therefore, it is non-metal; In sodium chloride, the yield of the sodium atom will be shifted to the chlorine atom.

I ask the guys: Is everything true in this scheme? What is the result of the connection of sodium and chlorine atoms in the NaCl molecule?

Students respond: the result of the compound of atoms in the NaCl molecule was the formation of a stable eight-electron outer level of the chlorine atom and the two-electron appearance of the sodium atom. Paradox: Two valence electrons at the external third energy level atom of sodium for nothing! (We work with a sodium atom scheme.)

It means that the sodium atom is "unprofitable" to connect with the chlorine atom, and NaCl compounds should not be in nature. However, students are known from the courses of geography and biology on the prevalence of cook salt on the planet and its role in the lives of living organisms.

How to find a way out of the current paradoxical situation?

We work with schemes of sodium and chlorine atoms, and students guess that the sodium atom does not be favorably disintegrated, and to give his valence electron at the chlorine atom. Then the sodium atom will be completed the second outside - the antishemis - energy level. At the chlorine atom, the external energy level will also be eight-electron:

We conclude: the atoms of a metal having a small number of valence electrons, it is advantageous to give, and not shift its valence electrons to non-metal atoms. Consequently, metal atoms do not possess electronegitability.

I propose to introduce an "sign of the capture" of someone else's valence electron by the nonmetal atom - a square bracket.

In the image of the valence electrons, the points of the diagram of the compound of metal and nonmetal atoms will look like this:

I draw the attention of students that when the valence electron is transferred from the metal atom (sodium) to the Nemetalla (chlorine) atoms, the atoms turn into ions.

Ions - charged particles in which atoms are converted as a result of transmission or addition of electrons.

The signs and values \u200b\u200bof the charges of ions and degrees of oxidation coincide, and the difference in the design is as follows:

1 –1
Na, Cl - for degrees of oxidation,

Na +, Cl - - for the charges of ions.

ABOUT B R A Z O V A N E F T O R I D A K A L C AND I CAF 2

Calcium - element IIA subgroup, it has two valence electrons, it is a metal. The calcium atom gives its own valence electrons at a fluorine - non-metallo, the electronest element itself.

In the scheme, we have unpaired valence electrons of atoms so that they "saw" each other and were able to form electronic couples:

The binding of calcium and fluorine atoms into the CAF 2 connection is energetically beneficial. As a result, both atoms have an eight-electron energy level: the fluorine is an external energy level, and calcium is the anticipatry. A schematic representation of electron transfer in atoms (useful when studying redox reactions):

I draw the attention of students that, like the attraction of negatively charged electrons to a positively charged atom core, oppositely charged ions are held by the power of electrostatic attraction.

Ionic compounds are solids with high temperatures melting. From life, students are known: you can noise the cook salt for a few hours. Flame temperature gas burner (~ 500 ° C) is not enough to melt salt
(t. PL (NaCl) \u003d 800 ° C). From here we conclude: the relationship between charged particles (ions) - ion connection is very durable.

We generalize: when the metal atoms are connected (M) with non-metal atoms (it), no displacement occurs, but the return of valence electrons atoms of metal atoms of non-metal.

At the same time, electron-ethyl atoms are converted into charged particles - ions, the charge of which coincides with the number of given (in the metal) and attached (in non-metal) electrons.

Thus, on the first of two lessons, the concept of "degree of oxidation" is formed, and the formation of the ionic compound is explained in the second. New concepts will serve as a good basis for further study of the theoretical material, namely: mechanisms for the formation of chemical bond, the dependence of the properties of substances from their composition and structure, consideration of oxidative reaction reactions.

In conclusion, I want to compare two methodological techniques: receiving the paradox and receiving the creation of problem situations in the lesson.

The paradoxical situation is created logically during the study of a new material. Her main plus is strong emotions, surprising students. Surprise - a powerful impetus to thinking at all. It "includes" involuntary attention, activates thinking, makes it explore and find ways to solve the question.

Colleagues, probably, will return: the creation of a problem situation in the lesson leads to the same. Provides, but not always! As a rule, a problematic issue is formulated by a teacher before learning a new material and stimulates not all students to work. Many remains incomprehensible, where this problem came from and why, in fact, it needs to be solved. The reception of the paradox is created during the study of a new material, encourages students to formulate the problem themselves, and therefore understand the origins of its occurrence and the need to solve.

I dare to assert that the reception of the paradox is the most successful way to revitalize the activities of students in the lessons, the development of research skills and creative abilities.