Chemical bond: definition, types, classification and features of the definition. Chemical bond: definition, types, properties

Characteristics of chemical bonds

The doctrine of chemical bonding forms the basis of all theoretical chemistry. A chemical bond is understood as the interaction of atoms that binds them into molecules, ions, radicals, and crystals. There are four types of chemical bonds: ionic, covalent, metallic and hydrogen. Different types of bonds can be found in the same substances.

1. In bases: between the oxygen and hydrogen atoms in hydroxo groups the bond is polar covalent, and between the metal and the hydroxo group it is ionic.

2. In salts of oxygen-containing acids: between the non-metal atom and the oxygen of the acidic residue - covalent polar, and between the metal and the acidic residue - ionic.

3. In ammonium, methylammonium, etc. salts, between the nitrogen and hydrogen atoms there is a polar covalent, and between ammonium or methylammonium ions and the acid residue - ionic.

4. In metal peroxides (for example, Na 2 O 2), the bond between the oxygen atoms is covalent, nonpolar, and between the metal and oxygen is ionic, etc.

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

Methods for forming a covalent bond

Covalent chemical bond is a bond that arises between atoms due to the formation of shared electron pairs.

Covalent compounds are usually gases, liquids, or relatively low-melting solids. One of the rare exceptions is diamond, which melts above 3,500 °C. This is explained by the structure of diamond, which is a continuous lattice of covalently bonded carbon atoms, and not a collection of individual molecules. In fact, any diamond crystal, regardless of its size, is one huge molecule.

A covalent bond occurs when the electrons of two nonmetal atoms combine. The resulting structure is called a molecule.

The mechanism of formation of such a bond can be exchange or donor-acceptor.

In most cases, two covalently bonded atoms have different electronegativity and the shared electrons do not belong to the two atoms equally. Most of the time they are closer to one atom than to another. In a hydrogen chloride molecule, for example, the electrons that form a covalent bond are located closer to the chlorine atom because its electronegativity is higher than that of hydrogen. However, the difference in the ability to attract electrons is not large enough for complete electron transfer from the hydrogen atom to the chlorine atom to occur. Therefore, the bond between hydrogen and chlorine atoms can be considered as a cross between an ionic bond (complete electron transfer) and a non-polar covalent bond (a symmetrical arrangement of a pair of electrons between two atoms). The partial charge on atoms is denoted Greek letterδ. Such a bond is called a polar covalent bond, and the hydrogen chloride molecule is said to be polar, that is, it has a positively charged end (hydrogen atom) and a negatively charged end (chlorine atom).

1. The exchange mechanism operates when atoms form shared electron pairs by combining unpaired electrons.

1) H 2 - hydrogen.

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

2) HCl - hydrogen chloride.

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

3) Cl 2: In a chlorine molecule covalent bond is formed due to unpaired p-electrons (overlapping p-p orbitals).

4) N ​​2: In the nitrogen molecule, three common electron pairs are formed between the atoms.

Donor-acceptor mechanism of covalent bond formation

Donor has an electron pair acceptor- free orbital that 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 according to the exchange mechanism, one - through the donor-acceptor mechanism. Covalent bonds are classified by the way the electron orbitals overlap, as well as by their displacement towards one of the bonded atoms. Chemical bonds formed as a result of overlapping electron orbitals along a bond line are called σ - connections(sigma bonds). The sigma bond is very strong.

The p orbitals can overlap in two regions, forming a covalent bond through lateral overlap.

Chemical bonds formed as a result of the “lateral” overlap of electron orbitals outside the bond line, i.e., in two regions, are called pi bonds.

According to the degree of displacement of common electron pairs to one of the atoms they connect, a covalent bond can be polar or non-polar. A covalent chemical bond formed between atoms with the same electronegativity is called non-polar. Electron pairs are not displaced towards any of the atoms, since atoms have the same electronegativity - the property of attracting valence electrons from other atoms. For example,

i.e., molecules are formed through a covalent nonpolar bond simple substances-non-metals. A covalent chemical bond between atoms of elements whose electronegativity differs is called polar.

For example, NH 3 is ammonia. Nitrogen is a more electronegative element than hydrogen, so the shared electron pairs are shifted towards its atom.

Characteristics of a covalent bond: bond length and energy

The characteristic properties of a covalent bond are its length and energy. Bond length is the distance between atomic nuclei. The shorter the length of a chemical bond, the stronger it is. However, a measure of bond strength is bond energy, which is determined by the amount of energy required to break the bond. It is usually measured in kJ/mol. Thus, according to experimental data, the bond lengths of the H 2, Cl 2 and N 2 molecules, respectively, are 0.074, 0.198 and 0.109 nm, and the bond energies, respectively, are 436, 242 and 946 kJ/mol.

Ions. Ionic bond

There are two main possibilities for an atom to obey the octet rule. The first of these is the formation of an ionic bond. (The second is the formation of a covalent bond, which will be discussed below). When an ionic bond is formed, a metal atom loses electrons, and a non-metal atom gains electrons.

Let's imagine that two atoms “meet”: an atom of a group I metal and a non-metal atom of group VII. A metal atom has a single electron at its outer energy level, while a non-metal atom just lacks one electron for its outer level to be complete. The first atom will easily give the second its electron, which is far from the nucleus and weakly bound to it, and the second will give it free place at its external electronic level. Then the atom, deprived of one of its negative charges, will become a positively charged particle, and the second will turn into a negatively charged particle due to the resulting electron. Such particles are called ions.

This is a chemical bond that occurs between ions. Numbers showing the number of atoms or molecules are called coefficients, and numbers showing the number of atoms or ions in a molecule are called indices.

Metal connection

Metals have specific properties, different from the properties of other substances. These properties are relatively high temperatures melting, ability to reflect light, high thermal and electrical conductivity. These features are due to the existence in metals special type connection - metal connection.

Metallic bond is a bond between positive ions in metal crystals, carried out due to the attraction of electrons moving freely throughout the crystal. The atoms of most metals at the outer level contain a small number of electrons - 1, 2, 3. These electrons come off easily, and the atoms turn into positive ions. The detached electrons move from one ion to another, binding them into a single whole. Connecting with ions, these electrons temporarily form atoms, then break off again and combine with another ion, etc. A process occurs endlessly, which can be schematically depicted as follows:

Consequently, in the volume of the metal, atoms are continuously converted into ions and vice versa. The bond in metals between ions through shared electrons is called metallic. The metallic bond has some similarities with the covalent bond, since it is based on the sharing of external electrons. However, with a covalent bond, the outer unpaired electrons of only two neighboring atoms are shared, while with a metallic bond, all atoms take part in the sharing of these electrons. That is why crystals with a covalent bond are brittle, but with a metal bond, as a rule, they are ductile, electrically conductive and have a metallic luster.

Metallic bonding is characteristic of both pure metals and mixtures of various metals - alloys in solid and liquid states. However, in the vapor state, metal atoms are connected to each other by a covalent bond (for example, sodium vapor fills yellow light lamps to illuminate the streets of large cities). Metal pairs consist of individual molecules (monatomic and diatomic).

A metal bond also differs from a covalent bond in strength: its energy is 3-4 times less than the energy of a covalent bond.

Bond energy is the energy required to break a chemical bond in all molecules that make up one mole of a substance. The energies of covalent and ionic bonds are usually high and amount to values ​​of the order of 100-800 kJ/mol.

Hydrogen bond

Chemical bond between positively polarized hydrogen atoms of one molecule(or parts thereof) and negatively polarized atoms of highly electronegative elements having shared electron pairs (F, O, N and less often S and Cl), another molecule (or parts thereof) is called hydrogen. Education mechanism hydrogen bond has partly electrostatic, partly d honoror-acceptor character.

Examples of intermolecular hydrogen bonding:

In the presence of such a connection, 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 carbonyl oxygen and the hydrogen of the amino group:

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

Substances with hydrogen bonds have molecular crystal lattices.

Atoms of most elements do not exist separately, as they can interact with each other. This interaction produces more complex particles.

The nature of a chemical bond is the action of electrostatic forces, which are the forces of interaction between electric charges. Electrons and atomic nuclei have such charges.

Electrons located on the outer electronic levels (valence electrons), being farthest from the nucleus, interact with it weakest, and therefore are able to break away from the nucleus. They are responsible for bonding atoms to each other.

Types of interactions in chemistry

Types of chemical bonds can be presented in the following table:

Characteristics of ionic bonding

Chemical reaction that occurs due to ion attraction having different charges is called ionic. This happens if the atoms being bonded have a significant difference in electronegativity (that is, the ability to attract electrons) and the electron pair goes to the more electronegative element. The result of this transfer of electrons from one atom to another is the formation of charged particles - ions. An attraction arises between them.

They have the lowest electronegativity indices typical metals, and the largest are typical non-metals. Ions are thus formed by the interaction between typical metals and typical nonmetals.

Metal atoms become positively charged ions (cations), donating electrons to their outer electron levels, and nonmetals accept electrons, thus turning into negatively charged ions (anions).

Atoms move into a more stable energy state, completing their electronic configurations.

The ionic bond is non-directional and non-saturable, since electrostatic interaction occurs in all directions, accordingly the ion can attract ions opposite sign in all directions.

The arrangement of the ions is such that around each there is a certain number of oppositely charged ions. The concept of "molecule" for ionic compounds doesn't make sense.

Examples of education

The formation of a bond in sodium chloride (nacl) is due to the transfer of an electron from the Na atom to the Cl atom to form the corresponding ions:

Na 0 - 1 e = Na + (cation)

Cl 0 + 1 e = Cl - (anion)

In sodium chloride, there are six chloride anions around the sodium cations, and six sodium ions around each chloride ion.

When interaction is formed between atoms in barium sulfide, the following processes occur:

Ba 0 - 2 e = Ba 2+

S 0 + 2 e = S 2-

Ba donates its two electrons to sulfur, resulting in the formation of sulfur anions S 2- and barium cations Ba 2+.

Metal chemical bond

The number of electrons in the outer energy levels of metals is small; they are easily separated from the nucleus. As a result of this detachment, metal ions and free electrons are formed. These electrons are called "electron gas". Electrons move freely throughout the volume of the metal and are constantly bound and separated from atoms.

The structure of the metal substance is as follows: the crystal lattice is the skeleton of the substance, and between its nodes electrons can move freely.

The following examples can be given:

Mg - 2e<->Mg 2+

Cs-e<->Cs+

Ca - 2e<->Ca2+

Fe-3e<->Fe 3+

Covalent: polar and non-polar

The most common type of chemical interaction is a covalent bond. The electronegativity values ​​of the elements that interact do not differ sharply; therefore, only a shift of the common electron pair to a more electronegative atom occurs.

Covalent interactions can be formed by an exchange mechanism or a donor-acceptor mechanism.

The exchange mechanism is realized if each of the atoms has unpaired electrons on the outer electronic levels and the overlap of atomic orbitals leads to the appearance of a pair of electrons that already belongs to both atoms. When one of the atoms has a pair of electrons on the outer electronic level, and the other has a free orbital, then when the atomic orbitals overlap, the electron pair is shared and interacts according to the donor-acceptor mechanism.

Covalent ones are divided by multiplicity into:

• simple or single;
• double;
• triples.

Double ones ensure the sharing of two pairs of electrons at once, and triple ones - three.

According to the distribution of electron density (polarity) between bonded atoms, a covalent bond is divided into:

• non-polar;
• polar.

A nonpolar bond is formed by identical atoms, and a polar bond is formed by different electronegativity.

The interaction of atoms with similar electronegativity is called a nonpolar bond. The common pair of electrons in such a molecule is not attracted to either atom, but belongs equally to both.

The interaction of elements differing in electronegativity leads to the formation of polar bonds. In this type of interaction, shared electron pairs are attracted to the more electronegative element, but are not completely transferred to it (that is, the formation of ions does not occur). As a result of this shift in electron density, partial charges appear on the atoms: the more electronegative one has a negative charge, and the less electronegative one has a positive charge.

Properties and characteristics of covalency

Main characteristics of a covalent bond:

• The length is determined by the distance between the nuclei of interacting atoms.
• Polarity is determined by the displacement of the electron cloud towards one of the atoms.
• Directionality is the property of forming bonds oriented in space and, accordingly, molecules having certain geometric shapes.
• Saturation is determined by the ability to form a limited number of bonds.
• Polarizability is determined by the ability to change polarity under the influence of an external electric field.
• The energy required to break a bond determines its strength.

An example of a covalent non-polar interaction can be the molecules of hydrogen (H2), chlorine (Cl2), oxygen (O2), nitrogen (N2) and many others.

H· + ·H → H-H molecule has a single non-polar bond,

O: + :O → O=O molecule has a double nonpolar,

Ṅ: + Ṅ: → N≡N the molecule is triple nonpolar.

Examples of covalent bonds of chemical elements include molecules of carbon dioxide (CO2) and carbon monoxide (CO), hydrogen sulfide (H2S), of hydrochloric acid(HCL), water (H2O), methane (CH4), sulfur oxide (SO2) and many others.

In the CO2 molecule, the relationship between carbon and oxygen atoms is covalent polar, since the more electronegative hydrogen attracts electron density. Oxygen has two unpaired electrons in its outer shell, while carbon can provide four valence electrons to form the interaction. As a result, double bonds are formed and the molecule looks like this: O=C=O.

In order to determine the type of bond in a particular molecule, it is enough to consider its constituent atoms. Simple metal substances form a metallic bond, metals with nonmetals form an ionic bond, simple nonmetal substances form a covalent nonpolar bond, and molecules consisting of different nonmetals form through a polar covalent bond.

Any interaction between atoms is possible only if there is a chemical bond. Such a connection is the reason for the formation of a stable polyatomic system - a molecular ion, molecule, crystal lattice. A strong chemical bond requires a lot of energy to break, which is why it is the basic quantity for measuring bond strength.

Conditions for the formation of a chemical bond

The formation of a chemical bond is always accompanied by the release of energy. This process occurs due to a decrease potential energy systems of interacting particles - molecules, ions, atoms. The potential energy of the resulting system of interacting elements is always less than the energy of unbound outgoing particles. Thus, the basis for the emergence of a chemical bond in a system is the decrease in the potential energy of its elements.

Nature of chemical interaction

A chemical bond is a consequence of the interaction of electromagnetic fields that arise around the electrons and atomic nuclei of those substances that take part in the formation of a new molecule or crystal. After the discovery of the theory of atomic structure, the nature of this interaction became more accessible to study.

For the first time, the idea of ​​​​the electrical nature of a chemical bond arose from the English physicist G. Davy, who suggested that molecules are formed due to the electrical attraction of oppositely charged particles. This idea interested the Swedish chemist and natural scientist I.Ya. Bercellius, who developed the electrochemical theory of the occurrence of chemical bonds.

The first theory, which explained the processes of chemical interaction of substances, was imperfect, and over time it had to be abandoned.

Butlerov's theory

A more successful attempt to explain the nature of the chemical bond of substances was made by the Russian scientist A.M. Butlerov. This scientist based his theory on the following assumptions:

• Atoms in the bonded state are bonded to each other in in a certain order. A change in this order causes the formation of a new substance.
• Atoms bond with each other according to the laws of valence.
• The properties of a substance depend on the order of connection of atoms in the molecule of the substance. A different arrangement causes a change in the chemical properties of the substance.
• Atoms connected to each other most strongly influence each other.

Butlerov's theory explained the properties of chemical substances not only by their composition, but also by the order of arrangement of atoms. Such internal order A.M. Butlerov called it “chemical structure”.

The theory of the Russian scientist made it possible to restore order in the classification of substances and provided the opportunity to determine the structure of molecules by their chemical properties. The theory also answered the question: why molecules containing the same number of atoms have different chemical properties.

Prerequisites for the creation of theories of chemical bonding

In his theory of chemical structure, Butlerov did not touch upon the question of what a chemical bond is. There was too little data available for this then. internal structure substances. Only after the discovery of the planetary model of the atom, the American scientist Lewis began to develop the hypothesis that a chemical bond arises through the formation of an electron pair that simultaneously belongs to two atoms. Subsequently, this idea became the foundation for the development of the theory of covalent bonds.

Covalent chemical bond

Sustainable chemical compound can be formed when the electron clouds of two neighboring atoms overlap. The result of such mutual intersection is an increasing electron density in the internuclear space. The nuclei of atoms, as we know, are positively charged, and therefore try to be drawn as close as possible to the negatively charged electron cloud. This attraction is much stronger than the repulsive forces between two positively charged nuclei, so this connection is stable.

Chemical bond calculations were first performed by chemists Heitler and London. They examined the bond between two hydrogen atoms. The simplest visual representation of it might look like this:

As you can see, the electron pair occupies a quantum place in both hydrogen atoms. This two-center arrangement of electrons is called a “covalent chemical bond.” Covalent bonds are typical for molecules of simple substances and their non-metal compounds. Substances created by covalent bonds usually do not conduct electricity or are semiconductors.

Ionic bond

An ionic chemical bond occurs when two oppositely charged ions attract each other. Ions can be simple, consisting of one atom of a substance. In compounds of this type, simple ions are most often positively charged metal atoms of groups 1 and 2 that have lost their electron. The formation of negative ions is inherent in the atoms of typical nonmetals and their acid bases. Therefore, among the typical ionic compounds there are many alkali metal halides, such as CsF, NaCl, and others.

Unlike a covalent bond, an ion is not saturated: a varying number of oppositely charged ions can join an ion or group of ions. The number of attached particles is limited only by the linear dimensions of the interacting ions, as well as the condition under which the attractive forces of oppositely charged ions must be greater than the repulsive forces of equally charged particles participating in the connection ionic type.

Hydrogen bond

Even before the creation of the theory of chemical structure, it was experimentally noticed that hydrogen compounds with various non-metals have somewhat unusual properties. For example, the boiling points of hydrogen fluoride and water are much higher than might be expected.

These and other features of hydrogen compounds can be explained by the ability of the H + atom to form another chemical bond. This type of connection is called a “hydrogen bond.” The reasons for the occurrence of a hydrogen bond lie in the properties of electrostatic forces. For example, in a hydrogen fluoride molecule, the total electron cloud is so shifted towards fluorine that the space around an atom of this substance is saturated with negative electric field. Around a hydrogen atom, deprived of its only electron, the field is much weaker and has a positive charge. As a result, an additional relationship arises between the positive fields of electron clouds H + and negative F - .

Chemical bond of metals

The atoms of all metals are located in space in a certain way. The arrangement of metal atoms is called a crystal lattice. In this case, electrons of different atoms weakly interact with each other, forming a common electron cloud. This type of interaction between atoms and electrons is called a “metallic bond.”

It is the free movement of electrons in metals that can explain physical properties metallic substances: electrical conductivity, thermal conductivity, strength, fusibility and others.

All currently known chemical elements located on the periodic table are divided into two: large groups: metals and non-metals. In order for them to become not just elements, but compounds, chemicals, could interact with each other, they must exist in the form of simple and complex substances.

This is why some electrons try to accept, while others try to give away. By replenishing each other in this way, the elements form different chemical molecules. But what keeps them together? Why do there exist substances of such strength that even the most serious instruments cannot be destroyed? Others, on the contrary, are destroyed by the slightest impact. All this is explained by the formation of various types of chemical bonds between atoms in molecules, the formation of a crystal lattice of a certain structure.

Types of chemical bonds in compounds

In total, there are 4 main types of chemical bonds.

1. Covalent nonpolar. It is formed between two identical non-metals due to the sharing of electrons, the formation of common electron pairs. Valence unpaired particles take part in its formation. Examples: halogens, oxygen, hydrogen, nitrogen, sulfur, phosphorus.
2. Covalent polar. Formed between two different non-metals or between a metal with very weak properties and a non-metal with weak electronegativity. It is also based on common electron pairs and the pulling of them toward itself by the atom whose electron affinity is higher. Examples: NH 3, SiC, P 2 O 5 and others.
3. Hydrogen bond. The most unstable and weakest, it is formed between a highly electronegative atom of one molecule and a positive atom of another. Most often this happens when substances are dissolved in water (alcohol, ammonia, etc.). Thanks to this connection, protein macromolecules can exist, nucleic acids, complex carbohydrates and so on.
4. Ionic bond. It is formed due to the forces of electrostatic attraction of differently charged metal and non-metal ions. The stronger the difference in this indicator, the more clearly the ionic nature of the interaction is expressed. Examples of compounds: binary salts, complex compounds - bases, salts.
5. A metal bond, the formation mechanism of which, as well as its properties, will be discussed further. It is formed in metals and their alloys of various kinds.

There is such a thing as the unity of a chemical bond. It just says that it is impossible to consider every chemical bond as a standard. They are all just conventionally designated units. After all, all interactions are based on a single principle - electron-static interaction. Therefore, ionic, metallic, covalent and hydrogen bonds have the same chemical nature and are only borderline cases of each other.

Metals and their physical properties

Metals are found in the overwhelming majority of all chemical elements. This is due to their special properties. A significant part of them was obtained by humans nuclear reactions in laboratory conditions, they are radioactive with a short half-life.

However, the majority are natural elements that form wholes. rocks and ores, are part of most important compounds. It was from them that people learned to cast alloys and make a lot of beautiful and important products. These are copper, iron, aluminum, silver, gold, chromium, manganese, nickel, zinc, lead and many others.

For all metals, common physical properties can be identified, which are explained by the formation of a metallic bond. What are these properties?

1. Malleability and ductility. It is known that many metals can be rolled even to the state of foil (gold, aluminum). Others produce wire, flexible metal sheets, and products that can be deformed during physical impact, but immediately restore their shape after it stops. It is these qualities of metals that are called malleability and ductility. The reason for this feature is the metal type of connection. The ions and electrons in the crystal slide relative to each other without breaking, which allows maintaining the integrity of the entire structure.
2. Metallic shine. It also explains the metallic bond, the formation mechanism, its characteristics and features. Thus, not all particles are able to absorb or reflect light waves of the same wavelength. The atoms of most metals reflect short-wave rays and acquire almost the same color of silver, white, and pale bluish tint. The exceptions are copper and gold, their colors are red-red and yellow, respectively. They are able to reflect longer wavelength radiation.
3. Thermal and electrical conductivity. These properties are also explained by the structure of the crystal lattice and the fact that the metallic type of bond is realized in its formation. Due to the “electron gas” moving inside the crystal, electric current and heat are instantly and evenly distributed between all atoms and ions and are conducted through the metal.
4. Solid state of aggregation under normal conditions. The only exception here is mercury. All other metals are necessarily strong, solid compounds, as well as their alloys. This is also a result of metallic bonding being present in metals. The mechanism of formation of this type of particle binding fully confirms the properties.

These are the main ones physical characteristics for metals, which are explained and determined precisely by the scheme of formation of a metallic bond. This method of connecting atoms is relevant specifically for metal elements and their alloys. That is, for them in solid and liquid states.

Metal type chemical bond

What is its peculiarity? The thing is that such a bond is formed not due to differently charged ions and their electrostatic attraction and not due to the difference in electronegativity and the presence of free electron pairs. That is, ionic, metallic, covalent bonds have slightly different natures and distinctive features of the particles being bonded.

All metals have the following characteristics:

• a small number of electrons per (except for some exceptions, which may have 6,7 and 8);
• large atomic radius;
• low ionization energy.

All this contributes to the easy separation of outer unpaired electrons from the nucleus. At the same time, the atom has a lot of free orbitals. The diagram of the formation of a metallic bond will precisely show the overlap of numerous orbital cells of different atoms with each other, which as a result form a common intracrystalline space. Electrons are fed into it from each atom, which begin to wander freely around different parts grates. Periodically, each of them attaches to an ion at a site in the crystal and turns it into an atom, then detaches again to form an ion.

Thus, a metallic bond is the bond between atoms, ions and free electrons in a common metal crystal. An electron cloud moving freely within a structure is called an “electron gas.” This is what explains most metals and their alloys.

How exactly does a metal chemical bond realize itself? Various examples can be given. Let's try to look at it on a piece of lithium. Even if you take it the size of a pea, there will be thousands of atoms. So let’s imagine that each of these thousands of atoms gives up its single valence electron to the common crystalline space. At the same time, knowing the electronic structure of a given element, you can see the number of empty orbitals. Lithium will have 3 of them (p-orbitals of the second energy level). Three for each atom out of tens of thousands - this is the common space inside the crystal in which the “electron gas” moves freely.

A substance with a metal bond is always strong. After all, electron gas does not allow the crystal to collapse, but only displaces the layers and immediately restores them. It shines, has a certain density (usually high), fusibility, malleability and plasticity.

Where else is metal bonding sold? Examples of substances:

• metals in the form of simple structures;
• all metal alloys with each other;
• all metals and their alloys in liquid and solid states.

There are simply an incredible number of specific examples, because metals in periodic table over 80!

Metal bond: mechanism of formation

If we consider it in general view, then we have already outlined the main points above. The presence of free electrons and electrons that are easily detached from the nucleus due to low ionization energy are the main conditions for the formation of this type of bond. Thus, it turns out that it is realized between the following particles:

• atoms at the sites of the crystal lattice;
• free electrons that were valence electrons in the metal;
• ions at the sites of the crystal lattice.

The result is a metal bond. The mechanism of formation is generally expressed next entry: Ме 0 - e - ↔ Ме n+ . From the diagram it is obvious what particles are present in the metal crystal.

The crystals themselves may have different shapes. It depends on the specific substance we are dealing with.

Types of metal crystals

This structure of a metal or its alloy is characterized by a very dense packing of particles. It is provided by ions in the crystal nodes. The lattices themselves can have different geometric shapes in space.

1. Body-centric cubic lattice - alkali metals.
2. Hexagonal compact structure - all alkaline earths except barium.
3. Face-centric cubic - aluminum, copper, zinc, many transition metals.
4. Mercury has a rhombohedral structure.
5. Tetragonal - indium.

The lower and lower it is located in the periodic system, the more complex its packaging and spatial organization of the crystal. In this case, the metallic chemical bond, examples of which can be given for each existing metal, is decisive in the construction of the crystal. Alloys have very diverse organizations in space, some of which have not yet been fully studied.

Communication characteristics: non-directional

Covalent and metallic bonds have one very pronounced distinctive feature. Unlike the first, the metallic bond is not directional. What does it mean? That is, the electron cloud inside the crystal moves completely freely within its boundaries in different directions, each electron is capable of attaching to absolutely any ion at the nodes of the structure. That is, interaction is carried out by different directions. Hence they say that the metallic bond is non-directional.

The mechanism of covalent bonding involves the formation of shared electron pairs, that is, clouds of overlapping atoms. Moreover, it occurs strictly along a certain line connecting their centers. Therefore, they talk about the direction of such a connection.

Saturability

This characteristic reflects the ability of atoms to have limited or unlimited interaction with others. Thus, covalent and metallic bonds are again opposites according to this indicator.

The first is saturable. The atoms taking part in its formation have a strictly defined number of valence external electrons, which are directly involved in the formation of the compound. It will not have more electrons than it has. Therefore, the number of bonds formed is limited by valence. Hence the saturation of the connection. Due to this characteristic, most compounds have a constant chemical composition.

Metallic and hydrogen bonds, on the contrary, are unsaturated. This is due to the presence of numerous free electrons and orbitals inside the crystal. Ions also play a role at the sites of the crystal lattice, each of which can become an atom and again an ion at any time.

Another characteristic of metallic bonding is the delocalization of the internal electron cloud. It manifests itself in the ability of a small number of shared electrons to bind together many atomic nuclei of metals. That is, the density is, as it were, delocalized, distributed evenly between all parts of the crystal.

Examples of bond formation in metals

Let's look at a few specific options that illustrate how a metallic bond is formed. Examples of substances are:

• zinc;
• aluminum;
• potassium;
• chromium.

Formation of a metallic bond between zinc atoms: Zn 0 - 2e - ↔ Zn 2+. The zinc atom has four energy levels. Based on the electronic structure, it has 15 free orbitals - 3 in p-orbitals, 5 in 4 d and 7 in 4f. Electronic structure the following: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 0 4d 0 4f 0, in total there are 30 electrons in the atom. That is, two free valence negative particles capable of moving within 15 spacious and unoccupied orbitals. And so it is for every atom. The result is a huge common space consisting of empty orbitals, and a small amount of electrons that bind the entire structure together.

Metallic bond between aluminum atoms: AL 0 - e - ↔ AL 3+. The thirteen electrons of an aluminum atom are located at three energy levels, which they clearly have in abundance. Electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 1 3d 0. Free orbitals - 7 pieces. Obviously, the electron cloud will be small compared to the total internal free space in the crystal.

Chrome metal bond. This item special in its electronic structure. Indeed, to stabilize the system, the electron falls from the 4s to the 3d orbital: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 4p 0 4d 0 4f 0 . There are 24 electrons in total, of which six are valence electrons. They are the ones who go into the common electronic space to form a chemical bond. There are 15 free orbitals, which is still much more than required to fill. Therefore, chromium is also a typical example of a metal with a corresponding bond in the molecule.

One of the most active metals, reacting even with plain water with combustion, is potassium. What explains these properties? Again, in many ways - by a metal type of connection. This element has only 19 electrons, but they are located at 4 energy levels. That is, in 30 orbitals of different sublevels. Electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 0 4p 0 4d 0 4f 0 . Only two with very low ionization energy. They break away freely and go into the common electronic space. There are 22 orbitals for movement per atom, that is, a very large free space for “electron gas”.

Similarities and differences with other types of connections

Generally this question already discussed above. One can only generalize and draw a conclusion. The main features of metal crystals that distinguish them from all other types of connections are:

• several types of particles taking part in the binding process (atoms, ions or atom-ions, electrons);
• different spatial geometric structures of crystals.

Metallic bonds have in common with hydrogen and ionic bonds unsaturation and non-directionality. With covalent polar - strong electrostatic attraction between particles. Separately from ionic - a type of particles at the nodes of a crystal lattice (ions). With covalent nonpolar - atoms in the nodes of the crystal.

Types of bonds in metals of different states of aggregation

As we noted above, a metallic chemical bond, examples of which are given in the article, is formed in two states of aggregation of metals and their alloys: solid and liquid.

The question arises: what type of bond is in metal vapors? Answer: covalent polar and non-polar. As with all compounds that are in the form of a gas. That is, when the metal is heated for a long time and transferred from solid state bonds in the liquid are not broken and the crystalline structure is preserved. However, when it comes to transferring the liquid into a vapor state, the crystal is destroyed and the metallic bond is converted into a covalent one.

.

You know that atoms can combine with each other to form both simple and complex substances. In this case, various types chemical bonds: 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.

Ionic 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.

Except halides alkali metals, 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).

Covalent nonpolar bond.

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.

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

Covalent polar bond.

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. Usually we depict the composition of water 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 also 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 and etc.). From organic chemistry courses 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.