What are the types of communication in chemistry. Chemical bond characteristics

The chemical bond arises due to the interaction of electric fields created by electrons and atomic nuclei, i.e. the chemical bond is electrical in nature.

Under chemical bond understand the result of the interaction of 2 or more atoms leading to the formation of a stable polyatomic system. A condition for the formation of a chemical bond is a decrease in the energy of interacting atoms, i.e. the molecular state of matter is energetically more favorable than the atomic state. When a chemical bond is formed, atoms tend to obtain a complete electron shell.

Distinguish: covalent, ionic, metallic, hydrogen and intermolecular.

Covalent bond- the most general form chemical bond arising from the socialization of an electron pair through exchange mechanism -, when each of the interacting atoms supplies one electron, or donor-acceptor mechanism, if an electron pair is transferred for general use by one atom (donor - N, O, Cl, F) to another atom (acceptor - atoms of d-elements).

Chemical bond characteristics.

1 - multiplicity of bonds - only 1 sigma bond is possible between 2 atoms, but along with it, there can be pi and delta bonds between the same atoms, which leads to the formation of multiple bonds. The multiplicity is determined by the number of common electron pairs.

2 - bond length - internuclear distance in a molecule, the greater the multiplicity, the shorter its length.

3 - bond strength is the amount of energy required to break it

4 - the saturation of the covalent bond is manifested in the fact that one atomic orbital can take part in the formation of only one c.s. This property determines the stoichiometry of molecular compounds.

5 - directionality of the c.with. depending on the shape and direction of the electron clouds in space, when they overlap, compounds with the linear and angular shape of molecules can be formed.

Ionic bond – formed between atoms that are very different in electronegativity. These are compounds of the main subgroups 1 and 2 of groups with elements of the main subgroups of 6 and 7 groups. Ionic is a chemical bond that occurs as a result of mutual electrostatic attraction of oppositely charged ions.

The mechanism of the formation of ionic bonds: a) the formation of ions of interacting atoms; b) the formation of a molecule due to the attraction of ions.

Non-directionality and unsaturation of the ionic bond

The force fields of the ions are evenly distributed in all directions; therefore, each ion can attract ions of the opposite sign to itself in any direction. This is the non-directionality of the ionic bond. The interaction of 2x ions of opposite sign does not lead to a complete mutual compensation of their force fields. Therefore, they retain the ability to attract ions in other directions, i.e. the ionic bond is characterized by unsaturation. Therefore, each ion in an ionic compound attracts such a number of ions of the opposite sign to form a crystal lattice of the ionic type. There are no molecules in an ionic crystal. Each ion is surrounded by a certain number of ions of a different sign (ion coordination number).

Metallic bond- chem. Bonding in metals. Metals have an excess of valence orbitals and a lack of electrons. When atoms approach each other, their valence orbitals overlap due to which electrons move freely from one orbital to another, and a bond is established between all metal atoms. The bond that is carried out by relatively free electrons between metal ions in the crystal lattice is called a metal bond. The bond is highly delocalized and lacks directionality and saturation, because valence electrons are evenly distributed throughout the crystal. The presence of free electrons determines the existence general properties metals: opacity, metallic luster, high electrical and thermal conductivity, malleability and ductility.

Hydrogen bond- the bond between the H atom and a strongly negative element (F, Cl, N, O, S). Hydrogen bonds can be intra- and intermolecular. BC is weaker than the covalent bond. The emergence of the sun is explained by the action of electrostatic forces. The H atom has a small radius and upon displacement or recoil of a single electron H acquires a strong positive charge, which acts on electronegativity.

Covalent bond - it is a bond between two atoms due to the formation of a common electron pair.

Covalent non-polar bond– this bond between atoms with equal

electronegativity. For example: H 2, O 2, N 2, Cl 2, etc. The dipole moment of such bonds is zero.

Covalent polar bond – this bond between atoms with different electronegativity. The overlapping zone of electron clouds is shifted towards the more electronegative atom.

For example, H – Cl (H b + → Cl b–).

A covalent bond has the following properties:

- saturation - the ability of an atom to form the number of chemical bonds corresponding to its valence;

- directivity - the overlap of electron clouds occurs in the direction providing the maximum overlap density.

Ionic bond– it is a bond between oppositely charged ions. It can be viewed as an extreme case of a covalent polar bond. Such a connection arises when there is a large difference in the electronegativities of atoms,

forming a chemical bond. For example, in the NaF molecule, the difference

electronegativities is 4.0 – 0.93 = 3.07, which leads to an almost complete transition of an electron from sodium to fluorine:

The interaction of ions of opposite sign does not depend on the direction, and the Coulomb forces do not possess the property of saturation. Because of this, the ionic bond does not have directionality and saturation.

Metallic bond– this is the connection of positively charged metal ions with free electrons.

Most metals have a number of properties that are general in nature and differ from those of other substances. These properties are relatively high melting points, ability to reflect light, high thermal and electrical conductivity. This is a consequence of the formation between metal atoms of a special type of bond - a metal bond.

In metal atoms, valence electrons are weakly bound to their nuclei and can easily be detached from them. As a result, positively charged metal ions and "free" electrons appear in the crystal lattice of the metal, the electrostatic interaction of which provides a chemical bond.

Hydrogen bond– it is a bond through a hydrogen atom bonded to a highly electronegative element.

The hydrogen atom associated with a highly electronegative element (fluorine, oxygen, nitrogen, etc.) gives up almost completely an electron from the valence orbital. The resulting free orbital can interact with the lone pair of electrons of another electronegative atom, resulting in a hydrogen bond. Using the example of water molecules and acetic acid hydrogen bond is shown by dashed lines:

This bond is much weaker than other chemical bonds (the energy of its formation is 10–40 kJ / mol). Hydrogen bonds can arise between different molecules and inside the molecule.

The hydrogen bond plays an extremely important role in such inorganic substances, like water, hydrofluoric acid, ammonia, etc., as well as in biological macromolecules.

Crystals.

There are four types of chemical bonds: ionic, covalent, metallic and hydrogen.

Ionic chemical bond

Ionic chemical bond is a bond formed due to the electrostatic attraction of cations to anions.

As you know, the most stable is the electronic configuration of atoms, in which there will be 8 electrons on the external electronic level, like the atoms of noble gases (or for the first energy level - 2). During chemical interactions, atoms tend to acquire just such a stable electronic configuration and often achieve this either as a result of the addition of valence electrons from other atoms (reduction process), or as a result of the return of their valence electrons (oxidation process). Atoms that have attached "foreign" electrons turn into negative ions, or anions. Atoms that donate their electrons turn into positive ions, or cations. It is clear that forces of electrostatic attraction arise between the anions and cations, which will hold them near each other, thereby realizing an ionic chemical bond.

Since cations form mainly metal atoms, and anions form nonmetal atoms, it is logical to conclude that this type of bond is characteristic of compounds of typical metals (elements of the main subgroups of groups I and II, except for magnesium and beryllium Be) with typical nonmetals (elements of the main subgroup VII group). A classic example is the formation of alkali metal halides (fluorides, chlorides, etc.). For example, consider the scheme for the formation of an ionic bond in sodium chloride:

Two oppositely charged ions, bound by attractive forces, do not lose the ability to interact with oppositely charged ions, as a result of which compounds with an ionic crystal lattice are formed. Ionic compounds are solid, strong, refractory substances with a high melting point.

Solutions and melts of most ionic compounds are electrolytes. This type of bond is characteristic of typical metal hydroxides and many salts of oxygen-containing acids. However, when an ionic bond is formed, an ideal (complete) transition of electrons does not occur. The ionic bond is an extreme case of the covalent polar bond.

In an ionic compound, ions are represented, as it were, in the form of electric charges with a spherical symmetry of an electric field, equally decreasing with increasing distance from the center of the charge (ion) in any direction. Therefore, the interaction of ions does not depend on the direction, that is, the ionic bond, in contrast to the covalent, will be non-directional.

The ionic bond also exists in ammonium salts, where there are no metal atoms (their role is played by the ammonium cation).

Covalent chemical bond

A covalent chemical bond is a bond that occurs between atoms due to the formation of common electron pairs.

Its description is also based on the concept of the acquisition by atoms chemical elements energetically favorable and stable electronic configuration of eight electrons (for a hydrogen atom of two). This configuration of atoms is obtained not through the donation or attachment of electrons, as in the case of ionic bonds, but through the formation of common electron pairs. The mechanism for the formation of such a bond can be exchange or donor-acceptor.

The exchange mechanism works when atoms form common electron pairs by combining unpaired electrons. For example:

1) H2 - hydrogen:

The bond arises due to the formation of a common electron pair by s-electrons of hydrogen atoms (overlapping of s-orbitals):

The bond arises due to the formation of a common electron pair of s- and p-electrons (overlapping of s-p-orbitals):

Let us consider the donor-acceptor mechanism of the formation of a covalent bond using the classical example of the formation of an ammonium ion NH4 +:

The donor has an electron pair, the acceptor has a free orbital pair, which this pair can occupy. In the ammonium ion, all four bonds with hydrogen atoms are covalent: three were formed due to the creation of common electron pairs by the nitrogen atom and hydrogen atoms by the exchange mechanism, one was formed by the donor-acceptor mechanism. All four bonds N-H in the ammonium cation are equivalent.

The donor-acceptor bond in the methylammonium ion [CH3NH3] + is formed similarly.

Covalent bonds are classified not only by the mechanism of formation of common electron pairs connecting atoms, but also by the method of overlapping electron orbits, by the number of common electron pairs, as well as by their displacement to one of the bonded atoms.

According to the method of overlapping electron orbitals, covalent bonds of sigma and pi are distinguished.

In a nitrogen molecule, one common electron pair is formed due to the sigma bond (the electron density is in one region located on the line connecting the nuclei of the atoms; the bond is strong).

The other two common electron pairs are formed due to n-bonds, that is, lateral overlap of p-orbitals in two regions; The pi bond is less strong than the sigma bond.

In a nitrogen molecule, there is one sigma bond and two pi bonds between the atoms, which are in mutually perpendicular planes (since 3 unpaired p-electrons of each atom interact).

Consequently, o-bonds can be formed due to the overlapping of electron orbitals:

and also due to the overlap of "pure" and hybrid orbitals:

sp 2 -sp 2 (C2H4), etc.

By the number of common electron pairs connecting atoms, that is, by the multiplicity, they are distinguished covalent bonds:

1) single:

2) double:
CO,

carbon monoxide (IV)

3) triple:
C2H2
HC = -CH acetylene

According to the degree of displacement of common electron pairs to one of the atoms connected by them, a covalent bond can be non-polar and polar. With a non-polar covalent bond, common electron pairs are not displaced to any of the atoms, since these atoms have the same electronegativity (EO) - the property to pull valence electrons away from other atoms.

A covalent chemical bond formed between atoms with the same electronegativity is called non-polar.
Through a covalent non-polar bond, molecules of simple non-metal substances are formed.

The values ​​of the relative electronegativity of phosphorus and hydrogen are practically the same: EO (H) = 2.1; EO (P) = = 2.1, therefore, in the phosphine PH3 molecule, the bonds between the phosphorus atom and the hydrogen atoms are covalent non-polar.

A covalent chemical bond between atoms of elements whose electronegativities differ is called polar

For example:

NH3
ammonia

Nitrogen is a more electronegative element than hydrogen, so the common electron pairs are shifted towards its atom.

A distinction should be made between the polarity of the molecule and the polarity of the bond. The polarity of a bond depends on the values ​​of the electronegativity of the linked atoms, and the polarity of a molecule depends on both the polarity of the bond and the geometry of the molecule. For example, bonds in a molecule carbon dioxide CO2 will be polar, and the molecule will not be polar, since it has a linear structure.

The H2O water molecule is polar, since it is formed with the help of two covalent polar bonds H-> 0 and has an angular shape. The HOH bond angle is 104.5 °, therefore, a negative pole of the molecule is formed for an oxygen atom with a partial negative charge of 6 and two lone electron pairs, and a positive pole for hydrogen atoms with a charge of 6+. The water molecule is a dipole.

Substances with a covalent bond are characterized by a crystal lattice of two types:

atomic - very durable (diamond, graphite, quartz); molecular - under normal conditions these are gases, volatile liquids and solid, but low-melting or sublimating substances (Cl2, H20, iodine I2, "dry ice" CO2, etc.).

The intramolecular covalent bond is strong, but the intermolecular interaction is very weak, as a result of which the molecular crystal lattice is fragile.

Metallic bond

The bond in metals and alloys, which is performed by relatively free electrons between metal ions in a metallic crystal lattice, is called metallic.

Such a bond is undirected, unsaturated, characterized by a small number of valence electrons and a large number of free orbitals, which is typical for metal atoms. Formation scheme of a metal bond (M - metal):

_
M 0 - ne<->M n +

The presence of a metal bond is due to physical properties metals and alloys: hardness, electrical and thermal conductivity, malleability, ductility, metallic luster. Substances with a metallic bond have a metallic crystal lattice. In its nodes are ions or metal atoms, between which electrons move freely (within the crystal) ("electron gas").

Hydrogen bond

The chemical bond between positively polarized hydrogen atoms of one molecule (or part of it) and negatively polarized atoms of strongly electronegative elements that have lone electron pairs of another molecule (or part of it) is called hydrogen.

The mechanism of hydrogen bond formation is partially electrostatic and partially donor-acceptor. In the presence of such a bond, even low-molecular substances can under normal conditions be liquids (alcohol, water) or easily liquefied gases (ammonia, hydrogen fluoride).

In biopolymers - proteins ( secondary structure) there is an intramolecular hydrogen bond between the carbonyl oxygen and the hydrogen of the amino group.

Polynucleotide molecules - DNA (deoxyribonucleic acid) are double helices in which two chains of nucleotides are hydrogen-bonded to each other. In this case, the principle of complementarity operates, that is, these bonds are formed between certain pairs consisting of purine and pyrimidine bases: against the adenine nucleotide (A) there is thymine (T), and against the guanine (G) - cytosine (C).

Substances with hydrogen bonds have molecular crystal lattices.

The uniform nature of the chemical bond

The division of chemical bonds into types is conditional, since they are all characterized by a certain unity.

The ionic bond can be considered as the limiting case of the covalent polar bond.

The metallic bond combines the covalent interaction of atoms with the help of shared electrons and the electrostatic attraction between these electrons and metal ions.

In substances, there are often no limiting cases of chemical bonds (or "pure" chemical bonds).

For example, lithium fluoride 1lK is referred to as ionic compounds. In fact, the bond in it is 80% ionic and 20% covalent. Therefore, it is more correct to speak about the degree of polarity (ionicity) of a chemical bond.

In the series of hydrogen halides HF - HCl - HBr - HI - HAt, the degree of bond polarity decreases, because the difference in the values ​​of electronegativity of halogen and hydrogen atoms decreases, and in hydrogen astate the bond becomes almost non-polar (EO (H) = 2.1; EO (Ar) = 2.2).

Different types of bonds can be contained in the same substances, for example:

1) in the bases - between the oxygen and hydrogen atoms in the hydroxyl groups, the bond is covalent polar, and between the metal and the hydroxyl group, it is ionic;

2) in salts oxygenated acids- between the atoms of the non-metal and the oxygen of the acid residue - covalent polar, and between the metal and the acid residue - ionic;

3) in salts of ammonium, methylammonium, etc. - between nitrogen and hydrogen atoms - covalent polar, and between ammonium or methylammonium ions and acid residue - ionic;

4) in metal peroxides (for example, Na 2 O 2) - the bond between oxygen atoms is covalent non-polar, and between metal and oxygen - ionic, etc.

Different types of links can go one into another:

At electrolytic dissociation in the water of covalent compounds, the covalent polar bond transforms into an ionic one;

When metals evaporate, the metal bond turns into a covalent non-polar, etc.

The reason for the unity of all types and types of chemical bonds is their identical physical nature- electron-nuclear interaction. The formation of a chemical bond in any case is the result of the electron-nuclear interaction of atoms, accompanied by the release of energy (Table 7).

Table 7 Types of chemical bonds

1. Often there is an expression: "Molecules of noble gases are monoatomic." How true is it?

2. Why, unlike most non-metallic elements, their brightest representatives - halogens - do not form allotropic modifications?

3. Give the most complete characterization of the chemical bond in the nitrogen molecule, using the following features: EO of bonded atoms, the mechanism of formation, the method of overlapping electron orbitals, the multiplicity of the bond.

4. Determine the type of chemical bond and consider the schemes of its formation in substances with the formulas: Ca, CaF2, F2, OF2.

5. Write down the structural formulas of substances: CO, CaC2, CS2, FeS2. Determine the oxidation state of the elements and their valence (if possible) in these substances.

6. Prove that all types of chemical bonds have a common nature.

7. Why are N2, CO and C2H2 molecules called isoelectronic?

Basic and additional textbooks

Chemical bond. The structure of matter.

Plan

1. Chemical bond: covalent (non-polar, polar; single, double, triple); ionic; metal; hydrogen; forces of intermolecular interaction.

2. Crystal lattices (molecular, ionic, atomic, metallic).

Different substances have different structures. Of all the substances known to date, only inert gases exist in the form of free (isolated) atoms, which is due to their high stability electronic structures... All other substances (and more than 10 million of them are currently known) are composed of bound atoms.

Chemical bond Are the forces of interaction between atoms or groups of atoms, leading to the formation of molecules, ions, free radicals, as well as ionic, atomic and metallic crystal lattices... By its nature, chemical bonds are electrostatic forces. The main role in the formation of a chemical bond between atoms is played by their valence electrons, that is, the electrons of the outer level, the least firmly bound to the nucleus. During the transition from the atomic state to the molecular one, energy is released, associated with the filling of free orbitals of the external electronic level with electrons to a certain stable state.

Exist different kinds chemical bond.

A covalent bond is a chemical bond carried out by the sharing of electron pairs... The theory of the covalent bond was proposed in 1916 by the American scientist Gilbert Lewis. Most molecules, molecular ions, free radicals and atomic crystal lattices are formed due to the covalent bond. A covalent bond is characterized by length (distance between atoms), directionality (a certain spatial orientation of electron clouds during the formation of a chemical bond), saturation (the ability of atoms to form a certain number of covalent bonds), energy (the amount of energy that must be spent to break a chemical bond).

The covalent bond can be non-polar and polar. Non-polar covalent bond occurs between atoms with the same electronegativity (EO) (H 2, O 2, N 2, etc.). In this case, the center of the total electron density is at the same distance from the nuclei of both atoms. Single, double and triple covalent bonds are distinguished by the number of common electron pairs (i.e., by multiplicity). If only one common electron pair is formed between two atoms, then such a covalent bond is called single. If two or three common electron pairs appear between two atoms, multiple bonds are formed - double and triple. A double bond consists of one β-bond and one β-bond. A triple bond consists of one β-bond and two β-bonds.

Covalent bonds, during the formation of which the overlapping region of electron clouds is on the line connecting the nuclei of atoms, are called -connections... Covalent bonds, during the formation of which the overlapping region of electron clouds is located on both sides of the line connecting the nuclei of atoms, are called - connections.

Education -connections can be involved s- and s- electrons (H 2), s- and p-electrons (HCl), R- and
R-electrons (Cl 2). In addition, β-bonds can be formed due to the overlap of "pure" and hybrid orbitals. Only R- and d-electrons.

The lines below show the chemical bonds in the molecules of hydrogen, oxygen and nitrogen:

where pairs of points (:) are paired electrons; "Crosses" (x) - unpaired electrons.

If a covalent bond is formed between atoms with different EO, then the center of the total electron density is shifted towards the atom with a higher EO. In this case covalent polar bond ... A diatomic molecule connected by a covalent polar bond is a dipole - an electrically neutral system in which the centers of positive and negative charges are at a certain distance from each other.

The graphic view of the chemical bonds in the molecules of hydrogen chloride and water is as follows:

where the arrows show the shift of the total electron density.

Polar and non-polar covalent bonds are formed by the exchange mechanism. In addition, there are donor-acceptor covalent bonds. Their formation mechanism is different. In this case, one atom (donor) provides a lone pair of electrons, which becomes a common electron pair between it and another atom (acceptor). When such a bond is formed, the acceptor provides a free electron orbital.

The donor-acceptor mechanism for the formation of a covalent bond is illustrated by the example of the formation of an ammonium ion:

Thus, in the ammonium ion, all four bonds are covalent. Three of them are formed by the exchange mechanism, one by the donor-acceptor mechanism. All four connections are equivalent, due to sp 3 -hybridization of the orbitals of the nitrogen atom. The valence of nitrogen in the ammonium ion is equal to IV, because it forms four bonds. Consequently, if an element forms bonds by both exchange and donor-acceptor mechanisms, then its valence is greater than the number of unpaired electrons and is determined by the total number of orbitals on the outer electron layer. For nitrogen, in particular, the highest valence is four.

Ionic bond – chemical bond between ions, carried out due to the forces of electrostatic attraction... An ionic bond is formed between atoms with a large EO difference (> 1.7); in other words, it is the relationship between typical metals and typical non-metals. The theory of ionic bonding was proposed in 1916 by the German scientist Walter Kossel. By donating their electrons, metal atoms turn into positively charged ions - cations; atoms of non-metals, accepting electrons, turn into negatively charged ions - anions... An electrostatic attraction arises between the formed ions, which is called ionic bond. The ionic bond is characterized by nondirectionality and unsaturation; for ionic compounds, the term "molecule" has no meaning. In the crystal lattice of ionic compounds, a certain number of ions with opposite charges are located around each ion. The compounds NaCl and FeS are characterized by a cubic crystal lattice.

The following shows the formation of an ionic bond using sodium chloride as an example:

The ionic bond is an extreme case of a polar covalent bond. There is no sharp boundary between them; the type of bond between atoms is determined by the difference in the electronegativity of the elements.

In the formation of simple substances - metals - atoms quite easily donate electrons to the external electronic level. Thus, in metal crystals, some of their atoms are in an ionized state. In the nodes of the crystal lattice there are positively charged ions and metal atoms, and between them - electrons, which can move freely throughout the crystal lattice. These electrons become common to all atoms and ions of the metal and are called "electron gas". The connection between all positively charged metal ions and free electrons in the crystal lattice of metals is called metal bond.

The presence of a metallic bond determines the physical properties of metals and alloys: hardness, electrical conductivity, thermal conductivity, malleability, plasticity, metallic luster. Free electrons can carry heat and electricity, so they are the reason for the main physical properties that distinguish metals from non-metals - high electrical and thermal conductivity.

Hydrogen bond occurs between molecules containing hydrogen and atoms with high EO (oxygen, fluorine, nitrogen). The covalent bonds H – O, H – F, H – N are strongly polar, due to which an excess positive charge accumulates on the hydrogen atom, and an excess negative charge at the opposite poles. Forces of electrostatic attraction - hydrogen bonds - arise between oppositely charged poles. Hydrogen bonds can be both intermolecular and intramolecular. The energy of a hydrogen bond is about ten times less than the energy of an ordinary covalent bond, but nevertheless, hydrogen bonds play an important role in many physicochemical and biological processes. In particular, DNA molecules are double helices in which two chains of nucleotides are linked by hydrogen bonds.

table

Intermolecular hydrogen bonds between water and hydrogen fluoride molecules can be depicted (by dots) as follows:

Substances with hydrogen bonds have molecular crystal lattices. The presence of a hydrogen bond leads to the formation of associates of molecules and, as a consequence, to an increase in the melting and boiling points.

In addition to the listed basic types of chemical bonds, there are also universal forces of interaction between any molecules that do not lead to rupture or the formation of new chemical bonds. These interactions are called van der Waals forces. They cause the attraction of molecules of a given substance (or various substances) to each other in liquid and solid states of aggregation.

Different types of chemical bonds determine the existence of different types of crystal lattices (table).

Substances consisting of molecules have molecular structure... Such substances include all gases, liquids, as well as solids with a molecular crystal lattice, such as iodine. Solids with an atomic, ionic or metallic lattice have non-molecular structure, there are no molecules in them.

A chemical bond is the force that holds the particles that form matter together.

Depending on the particles that hold these forces, bonds are subdivided into intramolecular and intermolecular.

Intramolecular bonds.

1. Covalent bond.

A covalent bond is a common electron pair between two nonmetal atoms.

Let us consider the example of a hydrogen molecule (H 2), in which a covalent bond is realized.

The hydrogen molecule consists of two hydrogen atoms (H), which have one electron at the external energy level:

Atoms tend to fill their orbitals completely. For this, two atoms combine. They share their unpaired electrons: a common electron pair is obtained. The electrons have become paired:

This shared electron pair is the covalent chemical bond. A covalent bond is indicated either by a line connecting atoms, or by two dots that indicate a common electron pair:

Imagine that there are two schoolmates. These are two atoms. They need to draw a picture that has red and Blue colour... They have a common pair of pencils (one red, the other blue) - this is a common electronic pair. Both deskmates use these pencils. Thus, these two neighbors are connected by a common pair of pencils, i.e. covalent chemical bond.

There are two mechanisms for the formation of a covalent chemical bond.

1. Exchange mechanism for the formation of a covalent bond.

In this case, each atom provides electrons to form a covalent bond. We considered this mechanism when we got acquainted with the covalent bond:

1. Donor-acceptor mechanism of covalent bond formation.

In this case, the total electron pair, so to speak, is unequal.

One atom has an LEP - a lone electron pair (two electrons in one orbital). And he provides it entirely for the formation of a covalent bond. This atom is called donor- because it provides both electrons to form a chemical bond.

And the second atom has only a free orbital. It accepts an electronic pair. This atom is called acceptor- it accepts both electrons.

A classic example is the formation of the ammonium ion NH 4 +. It is formed by the interaction of the H + ion and ammonia (NH 3). The hydrogen cation H + is an empty s-orbital.

This particle will be an acceptor.

The volume of nitrogen in ammonia has an LEP (lone electron pair).

The nitrogen atom in ammonia will donate:

In this case, both the blue and the red pencils were brought by one deskmate. He "treats" the second. And they both use pencils.

The specific reactions in which such an ion is formed will be discussed later in the relevant sections. For now, you just need to remember the principle by which a covalent bond is formed by the donor-acceptor mechanism.

There are two types of covalent bonds. Distinguish between covalent polar and non-polar bonds.

Covalent polar bond occurs between atoms non-metals with different values ​​of electronegativity. That is, between different atoms of non-metals.

An atom with a large electronegativity value will pull the common electron pair towards itself.

Covalent non-polar bond occurs between atoms non-metals with the same values ​​of electronegativity. This condition is satisfied if a bond occurs between atoms one chemical element-non-metal... Since the electronegativities of different atoms can be very close to each other, but they will still be different.

The common electron pair will not shift towards any atom, since each atom "pulls" it with the same force: the common electron pair will be in the middle.

And of course, a covalent bond can be single, double and triple:

1. Ionic bond.

An ionic bond occurs between metal and non-metal atoms. Since a metal and a non-metal have a large difference in electronegativity, the electron pair fully is drawn to a more electronegative atom - a non-metal atom.

The configuration of a fully filled energy level is not achieved due to the formation of a common electron pair. The non-metal takes the electron of the metal - it fills its outer level. And it is easier for the metal to donate its electrons (it has few of them) and it also has a completely filled level.

Thus, the metal, having donated electrons, acquires a negative charge, becomes a cation. And a non-metal, having received electrons, acquires a negative charge, becomes an anion.

Ionic chemical bond is electrostatic attraction of a cation to an anion.

Ionic bond takes place in metal salts, oxides and hydroxides. And in other substances in which a metal atom is associated with a non-metal atom (Li 3 N, CaH 2).

One important feature should be noted here: the ionic bond takes place between the cation and anions in all salts... In the most general way, we describe it as a metal-non-metal bond. But you need to understand that this is done only for simplicity. The salt may not contain a metal atom. For example, in ammonium salts (NH 4 Cl, (NH 4) 2 SO 4. The ammonium ion NH 4 + is attracted to the salt anion - this is an ionic bond.

Quite frankly, there is no ionic bond. An ionic bond is just an extreme degree of a covalent polar bond. Any bond has its own percentage of "ionicity" - it depends on the difference in electronegativity. But in school curriculum, and even more so in USE requirements ionic and covalent bonds are completely different concepts that cannot be confused.

1. Metallic bond.

All the splendor of the metallic bond can be understood only together with the metallic crystal lattice. Therefore, we will consider the metallic bond later, when we disassemble the crystal lattices.

All you need to know for now is that the metal bond is realized in simple substances - metals.

Intermolecular bonds.

Intermolecular bonds are much weaker than intramolecular ones, since they do not involve a common electron pair.

1. Hydrogen bonds.

Hydrogen bonds arise in substances in which a hydrogen atom is bonded to an atom with high value electronegativity (F, O, Cl, N).

In this case, the bond with hydrogen atoms becomes highly polar. An electron pair shifts from a hydrogen atom to a more electronegative atom. Due to this displacement, a partial positive charge (δ +) appears on the hydrogen, and a partial negative charge (δ-) on the electronegative atom.

For example, in a hydrogen fluoride molecule:

The δ + of one molecule attracts the δ- of another. This is the hydrogen bond. Graphically on the diagram, it is indicated by a dotted line:

A water molecule can form four hydrogen bonds:

Hydrogen bonds cause lower boiling and melting temperatures of substances between the molecules of which they arise. Compare hydrogen sulfide and water. There are hydrogen bonds in water - it is liquid under normal conditions, and hydrogen sulfide is a gas.

1. Van der Waals forces.

These are very weak intermolecular interactions. The principle of occurrence is the same as for hydrogen bonds. Very weak partial charges arise from oscillations of a common electron pair. And there are momentary forces of attraction between these charges.