Types of bonds between atoms of a substance. Types of chemical bonds: ionic, covalent, metallic

VALENCE BONDS METHOD

A covalent chemical bond is two-electron. The electrons involved in the formation of a chemical bond have opposite spins and form a common electron pair.

There are exchange and donor-acceptor mechanisms for the formation of a chemical bond:

1) Exchange - two atoms provide one electron each to form a common electron pair.

For example, the formation of hydrogen and hydrogen chloride molecules:

2) Donor-acceptor - one atom (donor) provides an electron pair, and the second (acceptor) provides a free orbital.

For example, the reaction of ammonia with a hydrogen ion to form an ammonium cation

According to the method of overlapping electron clouds, bonds are divided into σ-bond and π-bond:

1) the σ bond is formed due to the overlap of electron clouds along a straight line connecting the centers of interacting atoms. It can be between two s-clouds, two p-clouds, s- and p-clouds, or between s- and d-clouds.

2) the π bond is formed due to the overlap of electron clouds above and below the line connecting the centers of interacting atoms. It is formed mainly by overlapping p-orbitals.

The σ bond is stronger than the π bond.

Bond energy is the energy required to break a chemical bond. The energies of bond breakage and bond formation are equal in magnitude but opposite in sign. The higher the chemical bond energy, the more stable the molecule. Typically, binding energy is measured in kJ/mol.

For polyatomic compounds with bonds of the same type, the bond energy is taken to be its average value, calculated by dividing the energy of formation of a compound from atoms by the number of bonds. Thus, 432.1 kJ/∙mol is spent on breaking the H–H bond, and 1648 kJ/∙mol is spent on breaking four bonds in the CH 4 methane molecule, and in this case E C–H = 1648: 4 = 412 kJ/mol.

Bond length is the distance between the nuclei of interacting atoms in a molecule. It is measured in nm or A (angstrom = 10 -8 cm). It depends on the size of the electron shells and the degree of their overlap.

Bond polarity is the distribution of electrical charge between the atoms that form a chemical bond. To determine the polarity of a bond, it is necessary to compare the electronegativity of the atoms involved in the formation of the bond. If the electronegativity is the same, then the bond will be nonpolar, and in the case of different electronegativity, the bond will be polar. The extreme case of polar bonding, where the shared electron pair is almost entirely shifted to the more electronegative element, results in ionic bonding.

For example: Н–Н – non-polar, Н–Сl – polar and Na + –Сl - – ionic.

The displacement of an electron pair to a more electronegative atom results in the formation of a dipole. A dipole is a system of two equal but opposite charges located on opposite sides of a bond.

Molecule polarity is the vector sum of the dipole moments of all bonds of the molecule. It is necessary to distinguish between the polarities of individual bonds and the polarity of the molecule as a whole.

For example, a linear CO 2 molecule (O=C=O) is nonpolar, since the dipole moments of polar C=O bonds cancel each other out. The polarity of the water molecule means that it is nonlinear, that is, the dipole moments of the two O-H bonds do not cancel each other out, since they are located at an angle not equal to 180°.

Spatial structure of molecules - shape and location in space of electron clouds.

In compounds containing more than two atoms, an important characteristic is the bond angle formed by the chemical bonds in the molecule and reflecting its geometry.

Bond order is the number of chemical bonds between two atoms. The higher the bond order, the more tightly the atoms are connected to each other and the shorter the bond itself. A connection order higher than three does not occur. For example, the bond order in the molecules H 2, O 2 and N 2 is 1, 2 and 3, respectively, since the bond in these cases is formed due to the overlap of one, two and three pairs of electron clouds.

4. TYPES OF CHEMICAL BONDS

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

The number of chemical bonds is determined by the valences of the elements. The valence of an element is equal to the number of orbitals that take part in the formation of chemical bonds.

A covalent nonpolar bond is a bond achieved through the formation of electron pairs between atoms with practically equal electronegativity. For example, H 2, O 2, N 2, Cl 2, etc.

A covalent polar bond is a bond achieved through the formation of electron pairs between atoms with different electronegativity. For example, HCl, H 2 S, PH 3, etc.

A covalent bond has the following properties:

1) Saturation– the ability of an atom to form as many covalent bonds as it has valence orbitals.

2) Directions– the overlap of electron clouds occurs in the direction that provides the maximum overlap density.

4.2.An ionic bond is a bond between oppositely charged ions. It can be considered as an extreme case of covalent bonding. As a rule, she
formed between a metal and a non-metal.

Such a bond occurs when there is a large difference in the electronegativities of the interacting atoms. Ionic bonding does not have directionality or saturation.

The oxidation state is the conditional charge of an atom in a compound based on the assumption that complete ionization of the bonds occurs.

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, which 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.

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).

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.

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.

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. 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.

Chemical bond

All interactions leading to the combination of chemical particles (atoms, molecules, ions, etc.) into substances are divided into chemical bonds and intermolecular bonds (intermolecular interactions).

Chemical bonds- bonds directly between atoms. There are ionic, covalent and metallic bonds.

Intermolecular bonds- connections between molecules. These are hydrogen bonds, ion-dipole bonds (due to the formation of this bond, for example, the formation of a hydration shell of ions occurs), dipole-dipole (due to the formation of this bond, molecules of polar substances are combined, for example, in liquid acetone), etc.

Ionic bond- a chemical bond formed due to the electrostatic attraction of oppositely charged ions. In binary compounds (compounds of two elements), it is formed when the sizes of the bonded atoms are very different from each other: some atoms are large, others are small - that is, some atoms easily give up electrons, while others tend to accept them (usually these are atoms of the elements that form typical metals and atoms of elements forming typical nonmetals); the electronegativity of such atoms is also very different.
Ionic bonding is non-directional and non-saturable.

Covalent bond- a chemical bond that occurs due to the formation of a common pair of electrons. A covalent bond is formed between small atoms with the same or similar radii. A necessary condition is the presence of unpaired electrons in both bonded atoms (exchange mechanism) or a lone pair in one atom and a free orbital in the other (donor-acceptor mechanism):

A)	H· + ·H H:H	H-H	H 2	(one shared pair of electrons; H is monovalent);
b)		NN	N 2	(three shared pairs of electrons; N is trivalent);
V)		H-F	HF	(one shared pair of electrons; H and F are monovalent);
G)			NH4+	(four shared pairs of electrons; N is tetravalent)

simple (single)- one pair of electrons,
double- two pairs of electrons,
triples- three pairs of electrons.

Double and triple bonds are called multiple bonds.

According to the distribution of electron density between the bonded atoms, a covalent bond is divided into non-polar And polar. A non-polar bond is formed between identical atoms, a polar one - between different ones.

Electronegativity- a measure of the ability of an atom in a substance to attract common electron pairs.
The electron pairs of polar bonds are shifted towards more electronegative elements. The displacement of electron pairs itself is called bond polarization. The partial (excess) charges formed during polarization are designated + and -, for example: .

Based on the nature of the overlap of electron clouds ("orbitals"), a covalent bond is divided into -bond and -bond.
-A bond is formed due to the direct overlap of electron clouds (along the straight line connecting the atomic nuclei), -a bond is formed due to lateral overlap (on both sides of the plane in which the atomic nuclei lie).

A covalent bond is directional and saturable, as well as polarizable.
The hybridization model is used to explain and predict the mutual direction of covalent bonds.

Hybridization of atomic orbitals and electron clouds- the supposed alignment of atomic orbitals in energy, and electron clouds in shape when an atom forms covalent bonds.
The three most common types of hybridization are: sp-, sp 2 and sp 3 -hybridization. For example:
sp-hybridization - in molecules C 2 H 2, BeH 2, CO 2 (linear structure);
sp 2-hybridization - in molecules C 2 H 4, C 6 H 6, BF 3 (flat triangular shape);
sp 3-hybridization - in molecules CCl 4, SiH 4, CH 4 (tetrahedral form); NH 3 (pyramidal shape); H 2 O (angular shape).

Metal connection- a chemical bond formed by sharing the valence electrons of all bonded atoms of a metal crystal. As a result, a single electron cloud of the crystal is formed, which easily moves under the influence of electrical voltage - hence the high electrical conductivity of metals.
A metallic bond is formed when the atoms being bonded are large and therefore tend to give up electrons. Simple substances with a metallic bond are metals (Na, Ba, Al, Cu, Au, etc.), complex substances are intermetallic compounds (AlCr 2, Ca 2 Cu, Cu 5 Zn 8, etc.).
The metal bond does not have directionality or saturation. It is also preserved in metal melts.

Hydrogen bond- an intermolecular bond formed due to the partial acceptance of a pair of electrons from a highly electronegative atom by a hydrogen atom with a large positive partial charge. It is formed in cases where one molecule contains an atom with a lone pair of electrons and high electronegativity (F, O, N), and the other contains a hydrogen atom bound by a highly polar bond to one of such atoms. Examples of intermolecular hydrogen bonds:

H—O—H OH 2 , H—O—H NH 3 , H—O—H F—H, H—F H—F.

Intramolecular hydrogen bonds exist in the molecules of polypeptides, nucleic acids, proteins, etc.

A measure of the strength of any bond is the bond energy.
Communication energy- the energy required to break a given chemical bond in 1 mole of a substance. The unit of measurement is 1 kJ/mol.

The energies of ionic and covalent bonds are of the same order, the energy of hydrogen bonds is an order of magnitude less.

The energy of a covalent bond depends on the size of the bonded atoms (bond length) and on the multiplicity of the bond. The smaller the atoms and the greater the bond multiplicity, the greater its energy.

The ionic bond energy depends on the size of the ions and their charges. The smaller the ions and the greater their charge, the greater the binding energy.

Structure of matter

According to the type of structure, all substances are divided into molecular And non-molecular. Among organic substances, molecular substances predominate, among inorganic substances, non-molecular substances predominate.

Based on the type of chemical bond, substances are divided into substances with covalent bonds, substances with ionic bonds (ionic substances) and substances with metallic bonds (metals).

Substances with covalent bonds can be molecular or non-molecular. This significantly affects their physical properties.

Molecular substances consist of molecules connected to each other by weak intermolecular bonds, these include: H 2, O 2, N 2, Cl 2, Br 2, S 8, P 4 and other simple substances; CO 2, SO 2, N 2 O 5, H 2 O, HCl, HF, NH 3, CH 4, C 2 H 5 OH, organic polymers and many other substances. These substances do not have high strength, have low melting and boiling points, do not conduct electricity, and some of them are soluble in water or other solvents.

Non-molecular substances with covalent bonds or atomic substances (diamond, graphite, Si, SiO 2, SiC and others) form very strong crystals (with the exception of layered graphite), they are insoluble in water and other solvents, have high melting and boiling points, most of them they do not conduct electric current (except for graphite, which is electrically conductive, and semiconductors - silicon, germanium, etc.)

All ionic substances are naturally non-molecular. These are solid, refractory substances, solutions and melts of which conduct electric current. Many of them are soluble in water. It should be noted that in ionic substances, the crystals of which consist of complex ions, there are also covalent bonds, for example: (Na +) 2 (SO 4 2-), (K +) 3 (PO 4 3-), (NH 4 + )(NO 3-), etc. The atoms that make up complex ions are connected by covalent bonds.

Metals (substances with metallic bonds) very diverse in their physical properties. Among them there are liquid (Hg), very soft (Na, K) and very hard metals (W, Nb).

The characteristic physical properties of metals are their high electrical conductivity (unlike semiconductors, it decreases with increasing temperature), high heat capacity and ductility (for pure metals).

In the solid state, almost all substances are composed of crystals. Based on the type of structure and type of chemical bond, crystals (“crystal lattices”) are divided into atomic(crystals of non-molecular substances with covalent bonds), ionic(crystals of ionic substances), molecular(crystals of molecular substances with covalent bonds) and metal(crystals of substances with a metallic bond).

Tasks and tests on the topic "Topic 10. "Chemical bonding. Structure of matter."

Types of chemical bond - Structure of matter grade 8–9
Lessons: 2 Assignments: 9 Tests: 1
Assignments: 9 Tests: 1

After working through this topic, you should understand the following concepts: chemical bond, intermolecular bond, ionic bond, covalent bond, metallic bond, hydrogen bond, simple bond, double bond, triple bond, multiple bonds, non-polar bond, polar bond, electronegativity, bond polarization , - and -bond, hybridization of atomic orbitals, binding energy.

You must know the classification of substances by type of structure, by type of chemical bond, the dependence of the properties of simple and complex substances on the type of chemical bond and the type of “crystal lattice”.

You must be able to: determine the type of chemical bond in a substance, the type of hybridization, draw up diagrams of bond formation, use the concept of electronegativity, a number of electronegativity; know how electronegativity changes in chemical elements of the same period and one group to determine the polarity of a covalent bond.

After making sure that everything you need has been learned, proceed to completing the tasks. We wish you success.

Recommended reading:

O. S. Gabrielyan, G. G. Lysova. Chemistry 11th grade. M., Bustard, 2002.
G. E. Rudzitis, F. G. Feldman. Chemistry 11th grade. M., Education, 2001.

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, chemical substances, and be able to 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 various 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.

Covalent non-polar. 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.
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.
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, macromolecules of proteins, nucleic acids, complex carbohydrates, and so on can exist.
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.
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 through nuclear reactions in laboratory conditions; they are radioactive with a short half-life.

However, the majority are natural elements that form entire rocks and ores and 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?

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.
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.
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.
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 physical characteristics of 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 through different parts of the lattice. 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 (most often 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, since there are more than 80 metals in the periodic table!

Metal bond: mechanism of formation

If we consider it in general terms, 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 by the following notation: Me 0 - e - ↔ Me n+. From the diagram it is obvious what particles are present in the metal crystal.

The crystals themselves can 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.

Body-centric cubic lattice - alkali metals.
Hexagonal compact structure - all alkaline earths except barium.
Face-centric cubic - aluminum, copper, zinc, many transition metals.
Mercury has a rhombohedral structure.
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 in 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 valency. 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. The electronic structure is as follows: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 0 4d 0 4f 0, a total of 30 electrons in the atom. That is, two free valence negative particles are able to move 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 number 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 element is 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 that reacts even with ordinary water with fire 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

In general, this issue has already been 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 a solid to a liquid state, the bonds do not break 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.

Chemical bond name various types of interactions that determine the stable existence of two- and polyatomic compounds: molecules, ions, crystals and other substances. When a chemical bond is formed, the following occurs: a decrease in the total energy of a two- and polyatomic system compared to the sum of the energies of the isolated particles of which this system consists; redistribution of electron density in the region of a chemical bond compared to a simple superposition of the electron densities of unbonded atoms brought closer to the distance of the bond length.

Chemical bond energy E St. is the amount of energy released during bond formation (kJ/mol).

The higher the binding energy, the more stable the molecule, the stronger the bond.

An important characteristic of communication is link length 1 sv, equal to the distance between the nuclei of atoms in the compound. It depends on the size of the electron shells and the degree of their overlap. The connection is indicated by a dash, for example: H–J, O=O, H–C=C-H.

Octet rule. As a result of the formation of a chemical bond, atoms tend to acquire the same electronic configuration as that of the noble gases ns 2 nр 6, that is, eight electrons in the outer shell. For example, N 1s 2 2р 3 + 3 Н 1s 1 = NH 3.

3.1 Main types of chemical bonds

3.1.1 Covalent bond is a chemical bond formed by sharing a pair of electrons between two atoms. This reduces the energy of the system.

Features of a covalent chemical bond is its focus and saturation.

Focus covalent bonding is explained by the fact that atomic orbitals are spatially oriented and the overlap of electron clouds occurs in certain directions. It is expressed quantitatively in the form of bond angles between the directions of a chemical bond in a molecule.

Saturability is associated with the limitation of the number of electrons located on the outer shells, and determines the stoichiometry of molecular chemical compounds, on which the formula composition, mass ratios of elements, calculations using formulas and equations, etc. depend.

Polarity of covalent bond. A bond formed by identical atoms is called homeopolar, or nonpolar, since the shared electrons are evenly distributed between the atoms, for example, in molecules H 2, O 2, N 2, S 8.

If one of the atoms attracts electrons more strongly, then the electron pair moves towards it and the resulting bond is called covalentpolar.

The higher the electronegativity (EO) of an atom, the more likely it is that an electron pair will shift towards the nucleus of a given atom, therefore the difference in EO (ΔEO) of atoms characterizes the polarity of the bond. The atom to which the electron density shifts acquires an effective charge δ – , the second atom has an effective charge δ + . As a result, a dipole arises, having two charges of equal magnitude δ+ and δ-, and a dipole length of 1 D. A measure of the polarity of the connection is the electric moment of the dipole μ d = δ 1 D, C m, where δ is the effective charge, 1 D – dipole length. Debye D is used as a non-system unit for measuring μ , 1 D = 3.3·10 -30 C m.

Order of communication (multiplicity of communication) is the number of shared shared pairs between two bonded atoms. The higher the bond order, the more tightly the atoms are connected to each other and the shorter the bond itself.

For example, the bond order in the molecules H 2, O 2 and N 2 is 1, 2 and 3, respectively, since the bond in these cases is formed due to the overlap of one, two and three pairs of electron clouds.

AOs of both the same and different symmetries can take part in the formation of a covalent bond. When AOs overlap along the line of connection of atoms, a -bond is formed. The formation diagram of the -bond is shown in Figure 4.

s– s s–p p–p d–d

Figure 4 – diagram of -bond formation

When AOs overlap on both sides of the line of atomic connection, an  bond is formed. The formation diagram of the -bond is shown in Figure 5.

Figure 5 – diagram of the formation of -bonds -bonds