Nh3 is a type of chemical bond. What are the properties and name of the substance NH3? Metal connection

DEFINITION

Ammonia- hydrogen nitride.

Formula – NH 3. Molar mass – 17 g/mol.

Physical properties of ammonia

Ammonia (NH 3) is a colorless gas with a pungent odor (the smell of “ammonia”), lighter than air, highly soluble in water (one volume of water will dissolve up to 700 volumes of ammonia). The concentrated ammonia solution contains 25% (mass) ammonia and has a density of 0.91 g/cm 3 .

The bonds between atoms in the ammonia molecule are covalent. General view of the AB 3 molecule. All valence orbitals of the nitrogen atom enter into hybridization, therefore, the type of hybridization of the ammonia molecule is sp 3. Ammonia has a geometric structure of the AB 3 E type - a trigonal pyramid (Fig. 1).

Rice. 1. The structure of the ammonia molecule.

Chemical properties of ammonia

Chemically, ammonia is quite active: it reacts with many substances. The oxidation degree of nitrogen in ammonia “-3” is minimal, therefore ammonia exhibits only reducing properties.

When ammonia is heated with halogens, heavy metal oxides and oxygen, nitrogen is formed:

2NH 3 + 3Br 2 = N 2 + 6HBr

2NH 3 + 3CuO = 3Cu + N 2 + 3H 2 O

4NH 3 +3O 2 = 2N 2 + 6H 2 O

In the presence of a catalyst, ammonia can be oxidized to nitrogen oxide (II):

4NH 3 + 5O 2 = 4NO + 6H 2 O (catalyst - platinum)

Unlike hydrogen compounds of non-metals of groups VI and VII, ammonia does not exhibit acidic properties. However, hydrogen atoms in its molecule are still capable of being replaced by metal atoms. When hydrogen is completely replaced by a metal, compounds called nitrides are formed, which can also be obtained by direct interaction of nitrogen with the metal at high temperatures.

The main properties of ammonia are due to the presence of a lone pair of electrons on the nitrogen atom. A solution of ammonia in water is alkaline:

NH 3 + H 2 O ↔ NH 4 OH ↔ NH 4 + + OH —

When ammonia interacts with acids, ammonium salts are formed, which decompose when heated:

NH 3 + HCl = NH 4 Cl

NH 4 Cl = NH 3 + HCl (when heated)

Ammonia production

There are industrial and laboratory methods for producing ammonia. In the laboratory, ammonia is obtained by the action of alkalis on solutions of ammonium salts when heated:

NH 4 Cl + KOH = NH 3 + KCl + H 2 O

NH 4 + + OH - = NH 3 + H 2 O

This reaction is qualitative for ammonium ions.

Application of ammonia

Ammonia production is one of the most important technological processes worldwide. About 100 million tons of ammonia are produced annually in the world. Ammonia is released in liquid form or in the form of a 25% aqueous solution - ammonia water. The main areas of use of ammonia are the production of nitric acid (subsequent production of nitrogen-containing mineral fertilizers), ammonium salts, urea, hexamine, synthetic fibers (nylon and nylon). Ammonia is used as a refrigerant in industrial refrigeration units and as a bleaching agent in the cleaning and dyeing of cotton, wool and silk.

Examples of problem solving

EXAMPLE 1

3.3.1 Covalent bond is a two-center, two-electron bond formed due to the overlap of electron clouds carrying unpaired electrons with antiparallel spins. As a rule, it is formed between atoms of one chemical element.

It is quantitatively characterized by valency. Valency of the element - this is its ability to form a certain number of chemical bonds due to free electrons located in the atomic valence band.

A covalent bond is formed only by a pair of electrons located between atoms. It's called a split pair. The remaining pairs of electrons are called lone pairs. They fill the shells and do not take part in binding. The connection between atoms can be carried out not only by one, but also by two and even three divided pairs. Such connections are called double etc swarm - multiple connections.

3.3.1.1 Covalent nonpolar bond. A bond achieved through the formation of electron pairs that belong equally to both atoms is called covalent nonpolar. It occurs between atoms with practically equal electronegativity (0.4 > ΔEO > 0) and, therefore, a uniform distribution of electron density between the nuclei of atoms in homonuclear molecules. For example, H 2, O 2, N 2, Cl 2, etc. The dipole moment of such bonds is zero. The CH bond in saturated hydrocarbons (for example, in CH 4) is considered practically nonpolar, because ΔEO = 2.5 (C) - 2.1 (H) = 0.4.

3.3.1.2 Covalent polar bond. If a molecule is formed by two different atoms, then the overlap zone of electron clouds (orbitals) shifts towards one of the atoms, and such a bond is called polar . With such a bond, the probability of finding electrons near the nucleus of one of the atoms is higher. For example, HCl, H 2 S, PH 3.

Polar (unsymmetrical) covalent bond - bonding between atoms with different electronegativity (2 > ΔEO > 0.4) and asymmetric distribution of the common electron pair. Typically, it forms between two non-metals.

The electron density of such a bond is shifted towards a more electronegative atom, which leads to the appearance of a partial negative charge (delta minus) on it, and a partial positive charge (delta plus) on the less electronegative atom.

C ?  .

The direction of electron displacement is also indicated by an arrow:

CCl, CO, CN, OH, CMg.

The greater the difference in the electronegativity of the bonded atoms, the higher the polarity of the bond and the greater its dipole moment. Additional attractive forces act between partial charges of opposite sign. Therefore, the more polar the bond, the stronger it is.

Except polarizability covalent bond has the property saturation – the ability of an atom to form as many covalent bonds as it has energetically available atomic orbitals. The third property of a covalent bond is its direction.

3.3.2 Ionic bonding. The driving force behind its formation is the same desire of atoms for the octet shell. But in some cases, such an “octet” shell can only arise when electrons are transferred from one atom to another. Therefore, as a rule, an ionic bond is formed between a metal and a non-metal.

Consider, as an example, the reaction between sodium (3s 1) and fluorine (2s 2 3s 5) atoms. Electronegativity difference in NaF compound

EO = 4.0 - 0.93 = 3.07

Sodium, having given its 3s 1 electron to fluorine, becomes a Na + ion and remains with a filled 2s 2 2p 6 shell, which corresponds to the electronic configuration of the neon atom. Fluorine acquires exactly the same electronic configuration by accepting one electron donated by sodium. As a result, electrostatic attractive forces arise between oppositely charged ions.

Ionic bond - an extreme case of polar covalent bonding, based on the electrostatic attraction of ions. Such a bond occurs when there is a large difference in the electronegativity of the bonded atoms (EO > 2), when a less electronegative atom almost completely gives up its valence electrons and turns into a cation, and another, more electronegative atom, attaches these electrons and becomes an anion. The interaction of ions of the opposite sign does not depend on the direction, and Coulomb forces do not have the property of saturation. Due to this ionic bond has no spatial focus And saturation , since each ion is associated with a certain number of counterions (ion coordination number). Therefore, ionic-bonded compounds do not have a molecular structure and are solid substances that form ionic crystal lattices, with high melting and boiling points, they are highly polar, often salt-like, and electrically conductive in aqueous solutions. For example, MgS, NaCl, A 2 O 3. There are practically no compounds with purely ionic bonds, since a certain amount of covalency always remains due to the fact that a complete transfer of one electron to another atom is not observed; in the most “ionic” substances, the proportion of bond ionicity does not exceed 90%. For example, in NaF the bond polarization is about 80%.

In organic compounds, ionic bonds are quite rare, because A carbon atom tends neither to lose nor to gain electrons to form ions.

Valence elements in compounds with ionic bonds are very often characterized oxidation state , which, in turn, corresponds to the charge value of the element ion in a given compound.

Oxidation state - this is a conventional charge that an atom acquires as a result of the redistribution of electron density. Quantitatively, it is characterized by the number of electrons displaced from a less electronegative element to a more electronegative one. A positively charged ion is formed from the element that gave up its electrons, and a negative ion is formed from the element that accepted these electrons.

The element located in highest oxidation state (maximum positive), has already given up all of its valence electrons located in the AVZ. And since their number is determined by the number of the group in which the element is located, then highest oxidation state for most elements and will be equal group number . Concerning lowest oxidation state (maximum negative), then it appears during the formation of an eight-electron shell, that is, in the case when the AVZ is completely filled. For non-metals it is calculated by the formula Group number – 8 . For metals equal to zero , since they cannot accept electrons.

For example, the AVZ of sulfur has the form: 3s 2 3p 4. If an atom gives up all its electrons (six), it will acquire the highest oxidation state +6 , equal to the group number VI , if it takes the two necessary to complete the stable shell, it will acquire the lowest oxidation state –2 , equal to Group number – 8 = 6 – 8= –2.

3.3.3 Metal bond. Most metals have a number of properties that are general in nature and differ from the properties of other substances. Such properties are relatively high melting temperatures, the ability to reflect light, and high thermal and electrical conductivity. These features are explained by the existence of a special type of interaction in metals – metal connection.

In accordance with their position in the periodic table, metal atoms have a small number of valence electrons, which are rather weakly bound to their nuclei and can easily be detached from them. As a result, positively charged ions appear in the crystal lattice of the metal, localized in certain positions of the crystal lattice, and a large number of delocalized (free) electrons, moving relatively freely in the field of positive centers and communicating between all metal atoms due to electrostatic attraction.

This is an important difference between metallic bonds and covalent bonds, which have a strict orientation in space. Bonding forces in metals are not localized or directed, and free electrons forming an “electron gas” cause high thermal and electrical conductivity. Therefore, in this case it is impossible to talk about the direction of the bonds, since the valence electrons are distributed almost evenly throughout the crystal. This is what explains, for example, the plasticity of metals, i.e. the possibility of displacement of ions and atoms in any direction

3.3.4 Donor-acceptor bond. In addition to the mechanism of covalent bond formation, according to which a shared electron pair arises from the interaction of two electrons, there is also a special donor-acceptor mechanism . It lies in the fact that a covalent bond is formed as a result of the transition of an already existing (lone) electron pair donor (electron supplier) for the common use of the donor and acceptor (supplier of free atomic orbital).

Once formed, it is no different from covalent. The donor-acceptor mechanism is well illustrated by the scheme for the formation of the ammonium ion (Figure 9) (asterisks indicate the electrons of the outer level of the nitrogen atom):

Figure 9 - Scheme of formation of ammonium ion

The electronic formula of the ABZ of the nitrogen atom is 2s 2 2p 3, that is, it has three unpaired electrons that enter into a covalent bond with three hydrogen atoms (1s 1), each of which has one valence electron. In this case, an ammonia molecule NH 3 is formed, in which the lone electron pair of nitrogen is retained. If a hydrogen proton (1s 0), which has no electrons, approaches this molecule, then nitrogen will transfer its pair of electrons (donor) to this hydrogen atomic orbital (acceptor), resulting in the formation of an ammonium ion. In it, each hydrogen atom is connected to a nitrogen atom by a common electron pair, one of which is implemented via a donor-acceptor mechanism. It is important to note that H-N bonds formed by different mechanisms do not have any differences in properties. This phenomenon is due to the fact that at the moment of bond formation, the orbitals of the 2s and 2p electrons of the nitrogen atom change their shape. As a result, four orbitals of exactly the same shape appear.

Donors are usually atoms with a large number of electrons, but with a small number of unpaired electrons. For elements of period II, in addition to the nitrogen atom, such a possibility is available for oxygen (two lone pairs) and fluorine (three lone pairs). For example, the hydrogen ion H + in aqueous solutions is never in a free state, since the hydronium ion H 3 O + is always formed from water molecules H 2 O and the H + ion. The hydronium ion is present in all aqueous solutions, although for ease of writing it is preserved symbol H+.

3.3.5 Hydrogen bond. A hydrogen atom associated with a strongly electronegative element (nitrogen, oxygen, fluorine, etc.), which “pulls” a common electron pair onto itself, experiences a lack of electrons and acquires an effective positive charge. Therefore, it is able to interact with the lone pair of electrons of another electronegative atom (which acquires an effective negative charge) of the same (intramolecular bond) or another molecule (intermolecular bond). As a result, there is hydrogen bond , which is graphically indicated by dots:

This bond is much weaker than other chemical bonds (the energy of its formation is 10 – 40 kJ/mol) and mainly has a partially electrostatic, partially donor-acceptor character.

The hydrogen bond plays an extremely important role in biological macromolecules, such inorganic compounds as H 2 O, H 2 F 2, NH 3. For example, O-H bonds in H2O are noticeably polar in nature, with an excess of negative charge – on the oxygen atom. The hydrogen atom, on the contrary, acquires a small positive charge  + and can interact with the lone pairs of electrons of the oxygen atom of a neighboring water molecule.

The interaction between water molecules turns out to be quite strong, such that even in water vapor there are dimers and trimers of the composition (H 2 O) 2, (H 2 O) 3, etc. In solutions, long chains of associates of this type can appear:

because the oxygen atom has two lone pairs of electrons.

The presence of hydrogen bonds explains the high boiling temperatures of water, alcohols, and carboxylic acids. Due to hydrogen bonds, water is characterized by such high melting and boiling temperatures compared to H 2 E (E = S, Se, Te). If there were no hydrogen bonds, then water would melt at –100 °C and boil at –80 °C. Typical cases of association are observed for alcohols and organic acids.

Hydrogen bonds can occur both between different molecules and within a molecule if this molecule contains groups with donor and acceptor abilities. For example, it is intramolecular hydrogen bonds that play the main role in the formation of peptide chains, which determine the structure of proteins. H-bonds affect the physical and chemical properties of a substance.

Atoms of other elements do not form hydrogen bonds , since the forces of electrostatic attraction of opposite ends of dipoles of polar bonds (O-H, N-H, etc.) are rather weak and act only at short distances. Hydrogen, having the smallest atomic radius, allows such dipoles to get so close that the attractive forces become noticeable. No other element with a large atomic radius is capable of forming such bonds.

3.3.6 Intermolecular interaction forces (van der Waals forces). In 1873, the Dutch scientist I. Van der Waals suggested that there are forces that cause attraction between molecules. These forces were later called van der Waals forces – the most universal type of intermolecular bond. The energy of the van der Waals bond is less than the hydrogen bond and amounts to 2–20 kJ/∙mol.

Depending on the method of occurrence, forces are divided into:

1) orientational (dipole-dipole or ion-dipole) - occur between polar molecules or between ions and polar molecules. As polar molecules approach each other, they orient themselves so that the positive side of one dipole is oriented toward the negative side of the other dipole (Figure 10).

2) induction (dipole - induced dipole or ion - induced dipole) - arise between polar molecules or ions and non-polar molecules, but capable of polarization. Dipoles can affect non-polar molecules, turning them into indicated (induced) dipoles. (Figure 11).

3) dispersive (induced dipole - induced dipole) - arise between non-polar molecules capable of polarization. In any molecule or atom of a noble gas, fluctuations in electrical density occur, resulting in the appearance of instantaneous dipoles, which in turn induce instantaneous dipoles in neighboring molecules. The movement of instantaneous dipoles becomes consistent, their appearance and decay occur synchronously. As a result of the interaction of instantaneous dipoles, the energy of the system decreases (Figure 12).

NH3 is one of the most famous and useful chemicals. It has found wide application in the agricultural industry and beyond. It is distinguished by unique chemical properties, thanks to which it is used in various industries.

What is NH3

NH 3 is known even to the most ignorant of chemistry people. It's ammonia. Ammonia (NH 3) is otherwise called hydrogen nitride and is, under normal conditions, a colorless gas with a pronounced odor characteristic of this substance. It's also worth noting that NH 3 gas (called ammonia) is almost twice as light as air!

In addition to gas, it can be a liquid at a temperature of about 70 ° C or exist in the form of a solution (ammonia solution). A distinctive feature of liquid NH 3 is the ability to dissolve in itself the metals of the main subgroups I and II of groups of D.I. Mendeleev’s table of elements (that is, alkali and alkaline earth metals), as well as magnesium, aluminum, europium and ytterbium. Unlike water, liquid ammonia does not interact with the above elements, but acts precisely as a solvent. This property allows metals to be isolated in their original form through evaporation of the solvent (NH 3). In the figure below you can see what sodium dissolved in liquid ammonia looks like.

What does ammonia look like in terms of chemical bonds?

The diagram of ammonia (NH 3) and its spatial structure is most clearly shown by a triangular pyramid. The top of the ammonia “pyramid” is the nitrogen atom (highlighted in blue), as can be seen in the image below.

The atoms in a substance called ammonia (NH 3) are held together by hydrogen bonds, just like in a water molecule. But it is very important to remember that the bonds in the ammonia molecule are weaker than in the water molecule. This explains why the melting and boiling points of NH 3 are lower when compared to H 2 O.

Chemical properties

The most common 2 methods of producing NH 3 substance called ammonia. The industry uses the so-called Haber process, the essence of which is to bind air nitrogen and hydrogen (obtained from methane) by passing a mixture of these gases at high pressure over a heated catalyst.

In laboratories, ammonia synthesis is most often based on the interaction of concentrated ammonium chloride with solid sodium hydroxide.

Let's proceed to a direct examination of the chemical properties of NH 3.

1) NH 3 acts as a weak base. That is why the following equation describes the interaction with water:

NH 3 + H 2 O = NH4 + + OH -

2) Also based on the basic properties of NH 3 is its ability to react with acids and form the corresponding ammonium salts:

NH3 + HNO 3 = NH 4 NO 3 (ammonium nitrate)

3) Earlier it was said that a certain group of metals dissolves in liquid ammonia. However, some metals are also capable of not just dissolving, but forming compounds with NH 3 called amides:

Na (tv) + NH3 (g) = NaNH 2 + H 2

Na (solid) + NH3 (l) = NaNH 2 + H 2 (the reaction is carried out in the presence of iron as a catalyst)

4) When NH 3 interacts with the metals Fe 3+, Cr 3+, Al 3+, Sn 4+, Sn 2+, the corresponding metal hydroxides and ammonium cation are formed:

Fe 3+ + NH 3 + H 2 O = Fe(OH) 3 + NH 4 +

5) The result of the interaction of NH 3 with metals Cu 2+, Ni 2+, Co 2+, Pd 2+, Pt 2+, Pt 4+ most often are the corresponding metal complexes:

Cu 2+ + NH 3 + H 2 O = Cu(OH) 2 + NH 4 +

Cu(OH) 2 + NH 3 = 2 + + OH -

Formation and further path of NH3 in the human body

It is well known that amino acids are an integral part of biochemical processes in the human body. They are the main source of NH 3, a substance called ammonia, the result of their oxidative deamination (most often). Unfortunately, ammonia is toxic to the human body; it easily forms the above-mentioned ammonium cation (NH 4 +), which accumulates in cells. Subsequently, the most important biochemical cycles slow down, and as a result, the level of ATP produced decreases.

It is not difficult to guess that the body needs mechanisms for binding and neutralizing the released NH 3. The diagram below shows the sources and some of the binding products of ammonia in the human body.

So, speaking briefly, ammonia is neutralized through the formation of its transport forms in tissues (for example, glutamine and alanine), through excretion in urine, using urea biosynthesis, which is the main natural way of neutralizing NH 3 in the human body.

Application of NH3 - a substance called ammonia

In modern times, liquid ammonia is the most concentrated and cheapest nitrogen fertilizer, which is used in agriculture for ammoniation of coarse soils and peat. When liquid ammonia is added to the soil, the number of microorganisms increases, but there are no negative consequences, such as, for example, from solid fertilizers. The figure below shows one of the possible installations for liquefying ammonia gas using liquid nitrogen.

As liquid ammonia evaporates, it absorbs a lot of heat from the environment and causes cooling. This property is used in refrigeration units to produce artificial ice when storing perishable food products. In addition, it is used to freeze soil during the construction of underground structures. Aqueous solutions of ammonia are used in the chemical industry (it is an industrial non-aqueous solvent), laboratory practice (for example, as a solvent in the electrochemical production of chemical products), medicine and household use.

First of all, let's consider the structure of the ammonia molecule NH 3. As you already know, at the outer energy level, nitrogen atoms contain five electrons, of which three electrons are unpaired. It is they who participate in the formation of three covalent bonds with three hydrogen atoms during the formation of the ammonia molecule NH 3.

Three common electron pairs are shifted towards the more electronegative nitrogen atom, and since the ammonia molecule has the shape of a triangular pyramid (Fig. 128), as a result of the displacement of electron pairs, a dipole appears, i.e. a molecule with two poles.

Rice. 128.
The structure of the ammonia molecule

Ammonia molecules (in liquid ammonia) interact by bonding with each other:

This special type of chemical intermolecular bond, as you already know, is called a hydrogen bond.

Ammonia is a colorless gas with a pungent odor, almost twice as light as air. Ammonia should not be inhaled for long periods of time as it is poisonous. This gas easily liquefies at normal pressure and a temperature of -33.4 °C. When liquid ammonia evaporates from the environment, a lot of heat is absorbed, which is why ammonia is used in refrigeration units.

Ammonia is highly soluble in water: at 20 °C, about 710 volumes of ammonia dissolve in 1 volume of water (Fig. 129). A concentrated (25% by weight) aqueous solution of ammonia is called aqueous ammonia or ammonia water, and a 10% ammonia solution used in medicine is known as ammonia. In an aqueous solution of ammonia, a weak compound is formed - ammonia hydrate NH 3 H 2 O.

Rice. 129.
“Ammonia fountain” (dissolving ammonia in water)

If you add a few drops of phenolphthalein to an ammonia solution, the solution will turn crimson, indicating an alkaline environment. The alkaline reaction of aqueous solutions of ammonia is explained by the presence of hydroxide ions OH -:

If an ammonia solution colored with phenolphthalein is heated, the color will disappear (why?).

Laboratory experiment No. 30
Studying the properties of ammonia

Ammonia reacts with acids to form ammonium salts. This interaction can be observed in the following experiment: bring a glass rod or glass moistened with an ammonia solution to another rod or glass moistened with hydrochloric acid - thick white smoke will appear (Fig. 130):

Rice. 130.
"Smoke without fire"

So, after this, believe the saying that there is no smoke without fire.

Both an aqueous solution of ammonia and ammonium salts contain a special ion - ammonium cation NH + 4, which plays the role of a metal cation. The ammonium ion is formed as a result of the formation of a covalent bond between a nitrogen atom having a free (lone) electron pair and a hydrogen cation, which passes to ammonia from acid or water molecules:

When an ammonium ion is formed, the donor of a free electron pair is the nitrogen atom in ammonia, and the acceptor is the hydrogen cation of an acid or water.

You can predict another chemical property of ammonia yourself if you pay attention to the oxidation state of nitrogen atoms in it, namely -3. Of course, ammonia is the strongest reducing agent, that is, its nitrogen atoms can only give up electrons, but not accept them. Thus, ammonia can be oxidized either to free nitrogen (without the participation of a catalyst):

4NH 3 + 3O 2 = 2N 2 + 6H 2 O,

or to nitrogen oxide (II) (in the presence of a catalyst):

In industry, ammonia is produced by synthesis from nitrogen and hydrogen (Fig. 131).

Rice. 131.
Industrial installation (a) and scheme for industrial production of ammonia (b)

In the laboratory, ammonia is obtained by the action of slaked lime Ca(OH) 2 on ammonium salts, most often ammonium chloride:

The gas is collected in a vessel turned upside down, and is recognized either by smell, or by the blueness of wet red litmus paper, or by the appearance of white smoke when a stick moistened with hydrochloric acid is introduced.

Ammonia and its salts are widely used in industry and technology, agriculture, and everyday life. Their main areas of application are shown in Figure 132.

Rice. 132.
Application of ammonia and ammonium salts:
1.2 - in refrigeration units; 3 - production of mineral fertilizers; 4 - production of nitric acid; 5 - for soldering; 6 - production of explosives; 7 - in medicine and in everyday life (ammonia)

New words and concepts

1. The structure of the ammonia molecule.
2. Hydrogen bond.
3. Properties of ammonia: interaction with water, acids and oxygen.
4. Donor-acceptor mechanism for the formation of ammonium ion.
5. Receiving, collecting and recognizing ammonia.

.

You know that atoms can combine with each other to form both simple and complex substances. In this case, various types of chemical bonds are formed: ionic, covalent (non-polar and polar), metallic and hydrogen. One of the most essential properties of atoms of elements that determine what kind of bond is formed between them - ionic or covalent - This is electronegativity, i.e. the ability of atoms in a compound to attract electrons.

A conditional quantitative assessment of electronegativity is given by the relative electronegativity scale.

In periods, there is a general tendency for the electronegativity of elements to increase, and in groups - for their decrease. Elements are arranged in a row according to their electronegativity, on the basis of which the electronegativity of elements located in different periods can be compared.

The type of chemical bond depends on how large the difference in electronegativity values ​​of the connecting atoms of elements is. The more the atoms of the elements forming the bond differ in electronegativity, the more polar the chemical bond. It is impossible to draw a sharp boundary between the types of chemical bonds. In most compounds, the type of chemical bond is intermediate; for example, a highly polar covalent chemical bond is close to an ionic bond. Depending on which of the limiting cases a chemical bond is closer in nature, it is classified as either an ionic or a covalent polar bond.

An ionic bond is formed by the interaction of atoms that differ sharply from each other in electronegativity. For example, the typical metals lithium (Li), sodium (Na), potassium (K), calcium (Ca), strontium (Sr), barium (Ba) form ionic bonds with typical non-metals, mainly halogens.

In addition to alkali metal halides, ionic bonds also form in compounds such as alkalis and salts. For example, in sodium hydroxide (NaOH) and sodium sulfate (Na 2 SO 4) ionic bonds exist only between sodium and oxygen atoms (the remaining bonds are polar covalent).

When atoms with the same electronegativity interact, molecules with a covalent nonpolar bond are formed. Such a bond exists in the molecules of the following simple substances: H 2, F 2, Cl 2, O 2, N 2. Chemical bonds in these gases are formed through shared electron pairs, i.e. when the corresponding electron clouds overlap, due to the electron-nuclear interaction, which occurs when atoms approach each other.

When composing electronic formulas of substances, it should be remembered that each common electron pair is a conventional image of increased electron density resulting from the overlap of the corresponding electron clouds.

When atoms interact, the electronegativity values ​​of which differ, but not sharply, the common electron pair shifts to a more electronegative atom. This is the most common type of chemical bond, found in both inorganic and organic compounds.

Covalent bonds also fully include those bonds that are formed by a donor-acceptor mechanism, for example in hydronium and ammonium ions.

Metal connection.

The bond that is formed as a result of the interaction of relatively free electrons with metal ions is called a metallic bond. This type of bond is characteristic of simple substances - metals.

The essence of the process of metal bond formation is as follows: metal atoms easily give up valence electrons and turn into positively charged ions. Relatively free electrons detached from the atom move between positive metal ions. A metallic bond arises between them, i.e. Electrons, as it were, cement the positive ions of the crystal lattice of metals.

Hydrogen bond.

A bond that forms between the hydrogen atoms of one molecule and an atom of a strongly electronegative element(O,N,F) another molecule is called a hydrogen bond.

The question may arise: why does hydrogen form such a specific chemical bond?

This is explained by the fact that the atomic radius of hydrogen is very small. In addition, when displacing or completely donating its only electron, hydrogen acquires a relatively high positive charge, due to which the hydrogen of one molecule interacts with atoms of electronegative elements that have a partial negative charge that goes into the composition of other molecules (HF, H 2 O, NH 3) .

Let's look at some examples. We usually represent the composition of water with the chemical formula H 2 O. However, this is not entirely accurate. It would be more correct to denote the composition of water by the formula (H 2 O)n, where n = 2,3,4, etc. This is explained by the fact that individual water molecules are connected to each other through hydrogen bonds.

Hydrogen bonds are usually denoted by dots. It is much weaker than ionic or covalent bonds, but stronger than ordinary intermolecular interactions.

The presence of hydrogen bonds explains the increase in water volume with decreasing temperature. This is due to the fact that as the temperature decreases, the molecules become stronger and therefore the density of their “packing” decreases.

When studying organic chemistry, the following question arose: why are the boiling points of alcohols much higher than the corresponding hydrocarbons? This is explained by the fact that hydrogen bonds also form between alcohol molecules.

An increase in the boiling point of alcohols also occurs due to the enlargement of their molecules.

Hydrogen bonding is also characteristic of many other organic compounds (phenols, carboxylic acids, etc.). From courses in organic chemistry and general biology, you know that the presence of a hydrogen bond explains the secondary structure of proteins, the structure of the double helix of DNA, i.e. the phenomenon of complementarity.