The interaction of atoms of non-metal elements with each other is brief. "Interaction of atoms of non-metal elements with each other" (grade 8). Interaction with simple substances

We have already considered how atoms of metal elements interact with atoms of non-metal elements: some donate their outer electrons and turn into positive ions, while others accept electrons and turn into negative ions. Ions are attracted to each other, forming ionic compounds.

And how is the connection between the atoms of non-metal elements, which have a similar tendency to attach electrons, carried out? Let us first consider how the bond between atoms of the same chemical element is carried out, for example, in substances that have diatomic molecules: nitrogen N 2, hydrogen H 2, chlorine C1 2.

Please note that indices are also used to reflect the composition of these substances using chemical signs.

Two identical atoms of a non-metal element can combine into a molecule in only one way: by socializing their outer electrons, that is, by making them common to both atoms.

Consider, for example, the formation of a fluorine molecule F 2 .

Fluorine atoms - an element of the main subgroup of group VII (VIIA group) of the Periodic Table of Chemical Elements of D. I. Mendeleev - have seven electrons on the external energy level, and each atom lacks only one electron until it is completed. The outer electrons of the fluorine atom form three electron pairs and one unpaired electron:

If two atoms approach each other and each of them has one external unpaired electron, then these electrons “combine” and become common for both atoms, which thereby form a completed external eight-electron level.

The formation of a fluorine molecule is shown in the diagram:

If we designate a common electron pair with a dash, then the record is called a structural formula, for example, the structural formula of a fluorine molecule

Similarly to the fluorine molecule, a diatomic hydrogen molecule H 2 is also formed:

It should be taken into account that the two-electron level, similar to the completed level of the helium atom, will be completed for the hydrogen atom.

Structural formula of a hydrogen molecule

Let us refine our understanding of the covalent bond by the example of the formation of a hydrogen molecule, using the concept of an electron cloud (see § 9). When two hydrogen atoms approach each other, each having one s-electron cloud of a spherical shape, the electron clouds overlap. In this case, an area (place) arises where the density of the negative charge is the highest and therefore has an increased negative charge. Positively charged nuclei are attracted to it (this is known from the physics course), and a molecule is formed. Thus, the chemical bond is the result of the action of electrical forces. Let's represent the above in the form of a diagram:

It should be noted that the formation of a covalent bond, as well as the formation of an ionic bond, is based on the interaction of opposite charges.

In conclusion, let us consider the algorithm of reasoning necessary to write down the scheme for the formation of a covalent bond, for example, for the nitrogen molecule N 2 .

1. Nitrogen is an element of the main subgroup of the V group (VA group). Its atoms have five electrons at the outer level. To determine the number of unpaired electrons, we use the formula:

8 - N = number of unpaired electrons,

where N is the group number of the chemical element.

Therefore, nitrogen atoms will have (8-5 = 3) three unpaired electrons.

2. Let's write down the signs of chemical elements with the designation of external electrons so that unpaired electrons face the neighboring sign:

3. Let's write down the electronic and structural formulas of the resulting molecule:

If the atoms are interconnected by one common electron pair, then such a covalent bond is called single, if two - double, if three - triple.

The more common electron pairs the atoms in a molecule have, the stronger they are bound to each other and the smaller the distance between the nuclei of atoms, which is called the bond length. In fluorine molecules, the bond is single, and the bond length between the nuclei of atoms is 0.14 nanometers (1 nm = 10 -9 m, or 0.000000001 m). In nitrogen molecules, the bond is triple, and its length is 0.11 nm. It takes about seven times more energy to break a nitrogen molecule into individual atoms than it takes to break single bonds in a fluorine molecule.

Keywords and phrases

1. Atomic, or covalent, chemical bond.
2. Single, double and triple covalent chemical bonds.
3. Link length.
4. Electronic and structural formulas.

Work with computer

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

Questions and tasks

1. All elements of the main subgroup of group VII (VIIA group) of the Periodic Table of D. I. Mendeleev (fluorine subgroups) form simple substances consisting of diatomic molecules. Write down the electronic scheme of formation and the structural formula of such molecules, using a common chemical sign for the entire subgroup G (halogen).
2. Write down the schemes for the formation of chemical bonds for substances whose composition is displayed by the formulas KC1 and C1 2.
3. How many unpaired electrons do sulfur atoms have? What bond will be in S 2 molecules? Write down the scheme for the formation of a chemical bond in S 2 molecules.
4. Arrange in order of increasing strength of the chemical bond substances with the formulas S 2, Cl 2, N 2 and justify the correctness of your decision. How will the bond length change in the molecules of the series you compiled?
5. Divide the substances into two groups according to the type of chemical bond: N 2, Li 2 O, KC1, O 2, CaF 2, H 2.

I. Classification of chemical bonds

1. According to the mechanism of chemical bond formation

a) exchange when both atoms that form a bond provide unpaired electrons for it.

For example, the formation of hydrogen molecules H2 and chlorine Cl2:

b) donor - acceptor , when one of the atoms provides a ready pair of electrons (donor) to form a bond, and the second atom provides an empty free orbital.

For example, the formation of the ammonium ion (NH4)+ (charged particle):

2. According to the way the electron orbitals overlap

a) σ - connection (sigma), when the overlap maximum lies on the line connecting the centers of atoms.

For example,

H2 σ(s-s)

Cl2 σ(p-p)

HCl σ(s-p)

b) π - connections (pi), if the overlap maximum does not lie on the line connecting the centers of atoms.

3. According to the method of achieving the completed electron shell

Each atom tends to complete its outer electron shell, and there can be several ways to achieve such a state.

II. The essence of a covalent bond

covalent bond - this is a bond that occurs between atoms due to the formation of common electron pairs (For example, H2, HCl, H2O, O2).

According to the degree of displacement of common electron pairs to one of the atoms bound by them, a covalent bond can be polar and non-polar.

III. Covalent non-polar chemical bond

Covalent non-polar bond (CNS) - form atoms of the same chemical element - a non-metal(For example, H2, O2, O3).

Communication mechanism

Each atom of a nonmetal donates its outer unpaired electrons to another atom. Shared electron pairs are formed. An electron pair belongs equally to both atoms.

Consider the mechanism of formation of the chlorine molecule: Cl2- kns.

Electronic scheme for the formation of the Cl2 molecule:

Structural formula of the Cl2 molecule:

Cl - Cl, σ(p - p) - single bond

Demonstration of the formation of a hydrogen molecule

Consider the mechanism of formation of an oxygen molecule: O2 - kns.

Electronic scheme for the formation of the O2 molecule:

Structural formula of the O2 molecule:

O = O

π

In a molecule, a multiple, double bond:

One σ (p - p)

and one π (p - p)

Demonstration of the formation of oxygen and nitrogen molecules

IV. Tasks for fixing

Task number 1. Determine the types of chemical bonds in the molecules of the following substances:

H2S, KCl, O2, Na2S, Na2O, N2, NH3, CH4, BaF2, LiCl, O3, CO2, SO3, CCl4, F2.

Task number 2. Write the mechanism of formation of H2S, KCl, O2, Na2S, Na2O, N2, NH3, CH4, BaF2, LiCl, CCl4, F2 molecules. In the case of a covalent bond, determine the type of overlap of electron clouds (π or σ), as well as the formation mechanism (exchange or donor-acceptor)

Topic: Covalent non-polar bond

Tasks:

To form an idea of ​​a covalent bond, in particular a covalent non-polar bond;

Show the mechanism of formation of a covalent non-polar bond;

Continue developing the skills to analyze, draw conclusions;

Cultivate a culture of communication.

Motivation and goal setting:

Why does nitrogen or hydrogen exist as diatomic molecules? During the conversation, we carry out joint goal-setting and determine the topic of the lesson.

Learning new material:

Let's look at how a chemical bond is formed in a molecule.Cl 2.

The chlorine atom is inVIIAgroup of the Periodic Table, which means that it has seven electrons in the outer energy level and it lacks only one electron to complete it. Six electrons of the outer level form pairs, and one is unpaired. Two chlorine atoms, which have one unpaired electron each, approach, these electrons “combine” and become common for both atoms, while the level becomes complete - eight electrons. A common pair of electrons can be denoted simply by a dash.

Therefore, a covalent bond, or atomic bond, is a chemical bond resulting from the formation of common electron pairs.

This chemical bond is formed between atoms of the same non-metal, while the common electron pairs that have formed belong to both atoms equally and none of them will have either an excess or a lack of a negative charge, therefore this covalent bond is called non-polar.

Similarly, an H molecule is formed 2. However, the hydrogen atom is inIAgroup, so each hydrogen atom has only one electron, and before the completion of the external energy level, it lacks only one electron (recall that for hydrogen and helium atoms, the level is considered complete if it has 2 electrons). Each hydrogen atom has one electron, and these unpaired electrons combine to form a common electron pair, which can also be denoted as a dash.

In addition, when two hydrogen atoms approach, each of which has one s-electron cloud of a spherical shape, these electron clouds overlap. In this case, a region is formed where the negative charge density is high, positively charged nuclei are attracted to it, and a molecule is formed.

Let's consider the mechanism of formation of a more complex molecule O 2 .

The oxygen is inVIAgroup, so it has 6 electrons in the outer level. And in order to determine the number of unpaired electrons, you can use the formula 8 -N, whereN– group number. Therefore, each oxygen atom will have 2 unpaired electrons, which will participate in the formation of a chemical bond. These two unpaired electrons combine with two other unpaired electrons of another atom and two common electron pairs are formed, which can be conventionally depicted as two dashes.

Since the bond in an oxygen molecule consists of two electron pairs, it is also called a double bond, it will be stronger than a single bond, as in a hydrogen molecule. But you need to understand that the stronger the bond between atoms in a molecule, the smaller the distance between the nuclei of atoms. This distance is called the bond length. A triple bond is even shorter than a double bond, but much stronger. For example, in a nitrogen molecule, a triple bond, in order to divide the molecule into two atoms, it is necessary to expend seven times more energy than to break a single bond in a chlorine molecule.

Generalization and systematization of knowledge:

What chemical bond is called a covalent bond?

Between the atoms of which elements a covalent non-polar bond is formed?

What is the essence of the formation of a covalent bond?

How is a single bond different from a double or triple bond?

What does the bond length show and what does it depend on?

Consolidation and control of knowledge:

Make schemes for the formation of molecules of substances: a) bromine; b) fluorine; c) nitrogen.

Eliminate the excess from each row:

a) CO 2 , NH 3 , P 4 , P 2 O 5 ;

b)Cl 2 , S, N 2 , CO 2 .

Answer:

a)P 4 ; b)Cl 2 , S, N 2 . These are substances with a covalent non-polar bond.

Select substances with a covalent non-polar bond:

P 4 , H 2 S, NH 3 , P 2 O 3 , S, N 2 , O 2 , H 2 O, HCl, H 2 .

Answer: substances with a covalent non-polar bond are formed by the same atoms of non-metals, so these will beP 4 , S, N 2 , O 2 , H 2 .

Reflection and summing up:

How do you think the lesson material was learned? a) excellent; b) good; c) satisfactory; d) not learned.

Can you now answer the question we asked at the beginning of the lesson?

Homework:

Ilevel: §11, ex. thirteen;

IIlevel: also + ex. 4, 5.