There is no unified theory of chemical bonds; chemical bonds are conventionally divided into covalent (a universal type of bond), ionic (a special case of a covalent bond), metallic and hydrogen.
Covalent bond
The formation of a covalent bond is possible by three mechanisms: exchange, donor-acceptor and dative (Lewis).
According to metabolic mechanism The formation of a covalent bond occurs due to the sharing of common electron pairs. In this case, each atom tends to acquire a shell of an inert gas, i.e. obtain a completed external energy level. The formation of a chemical bond by exchange type is depicted using Lewis formulas, in which each valence electron of an atom is represented by dots (Fig. 1).
Rice. 1 Formation of a covalent bond in the HCl molecule by the exchange mechanism
With the development of the theory of atomic structure and quantum mechanics, the formation of a covalent bond is represented as the overlap of electronic orbitals (Fig. 2).
Rice. 2. Formation of a covalent bond due to the overlap of electron clouds
The greater the overlap of atomic orbitals, the stronger the bond, the shorter the bond length, and the greater the bond energy. A covalent bond can be formed by overlapping different orbitals. As a result of the overlap of s-s, s-p orbitals, as well as d-d, p-p, d-p orbitals with lateral lobes, the formation of bonds occurs. A bond is formed perpendicular to the line connecting the nuclei of 2 atoms. One and one bond are capable of forming a multiple (double) covalent bond, characteristic of organic substances of the class of alkenes, alkadienes, etc. One and two bonds form a multiple (triple) covalent bond, characteristic of organic substances of the class of alkynes (acetylenes).
Formation of a covalent bond by donor-acceptor mechanism Let's look at the example of the ammonium cation:
NH 3 + H + = NH 4 +
7 N 1s 2 2s 2 2p 3
The nitrogen atom has a free lone pair of electrons (electrons not involved in the formation of chemical bonds within the molecule), and the hydrogen cation has a free orbital, so they are an electron donor and acceptor, respectively.
Let us consider the dative mechanism of covalent bond formation using the example of a chlorine molecule.
17 Cl 1s 2 2s 2 2p 6 3s 2 3p 5
The chlorine atom has both a free lone pair of electrons and vacant orbitals, therefore, it can exhibit the properties of both a donor and an acceptor. Therefore, when a chlorine molecule is formed, one chlorine atom acts as a donor and the other as an acceptor.
Main characteristics of a covalent bond are: saturation (saturated bonds are formed when an atom attaches as many electrons to itself as its valence capabilities allow; unsaturated bonds are formed when the number of attached electrons is less than the valence capabilities of the atom); directionality (this value is related to the geometry of the molecule and the concept of “bond angle” - the angle between bonds).
Ionic bond
There are no compounds with a pure ionic bond, although this is understood as a chemically bonded state of atoms in which a stable electronic environment of the atom is created when the total electron density is completely transferred to the atom of a more electronegative element. Ionic bonding is possible only between atoms of electronegative and electropositive elements that are in the state of oppositely charged ions - cations and anions.
DEFINITION
Ion are electrically charged particles formed by the removal or addition of an electron to an atom.
When transferring an electron, metal and nonmetal atoms tend to form a stable electron shell configuration around their nucleus. A non-metal atom creates a shell of the subsequent inert gas around its core, and a metal atom creates a shell of the previous inert gas (Fig. 3).
Rice. 3. Formation of an ionic bond using the example of a sodium chloride molecule
Molecules in which ionic bonds exist in their pure form are found in the vapor state of the substance. The ionic bond is very strong, and therefore substances with this bond have a high melting point. Unlike covalent bonds, ionic bonds are not characterized by directionality and saturation, since the electric field created by ions acts equally on all ions due to spherical symmetry.
Metal connection
The metallic bond is realized only in metals - this is the interaction that holds metal atoms in a single lattice. Only the valence electrons of the metal atoms belonging to its entire volume participate in the formation of a bond. In metals, electrons are constantly stripped from atoms and move throughout the entire mass of the metal. Metal atoms, deprived of electrons, turn into positively charged ions, which tend to accept moving electrons. This continuous process forms the so-called “electron gas” inside the metal, which firmly binds all the metal atoms together (Fig. 4).
The metallic bond is strong, therefore metals are characterized by a high melting point, and the presence of “electron gas” gives metals malleability and ductility.
Hydrogen bond
A hydrogen bond is a specific intermolecular interaction, because its occurrence and strength depend on the chemical nature of the substance. It is formed between molecules in which a hydrogen atom is bonded to an atom with high electronegativity (O, N, S). The occurrence of a hydrogen bond depends on two reasons: firstly, the hydrogen atom associated with an electronegative atom does not have electrons and can easily be incorporated into the electron clouds of other atoms, and, secondly, having a valence s-orbital, the hydrogen atom is able to accept a lone pair electrons of an electronegative atom and form a bond with it through the donor-acceptor mechanism.
Substances with a molecular structure are formed using a special type of interconnection. A covalent bond in a molecule, polar or non-polar, is also called an atomic bond. This name comes from the Latin “co” - “together” and “vales” - “having force”. In this method of forming compounds, a pair of electrons is shared between two atoms.
What are polar and nonpolar covalent bonds? If a new compound is formed in this way, thensocialization of electron pairs. Typically, such substances have a molecular structure: H 2, O 3, HCl, HF, CH 4.
There are also non-molecular substances in which the atoms are connected in this way. These are the so-called atomic crystals: diamond, silicon dioxide, silicon carbide. In them, each particle is connected to four others, resulting in a very strong crystal. Crystals with a molecular structure are usually not very strong.
Properties of this method of forming compounds:
- multiplicity;
- direction;
- degree of polarity;
- polarizability;
- pairing.
Multiplicity is the number of electron pairs shared. There can be from one to three. Oxygen does not have enough electrons to fill its shell, so it will be double. In nitrogen molecule N2 it is triple.
Polarizability - the possibility of forming a covalent polar bond and a non-polar one. Moreover, it can be more or less polar, closer to ionic or vice versa - this is the property of the degree of polarity.
Directionality means that atoms tend to connect in such a way that there remains as much electron density between them as possible. It makes sense to talk about directionality when p or d orbitals are connected. S-orbitals are spherically symmetrical, for them all directions are equivalent. In p-orbitals, the nonpolar or polar covalent bond is directed along their axis, so that the two “eights” overlap at the vertices. This is a σ bond. There are also less strong π bonds. In the case of p-orbitals, the “eight” orbitals are overlapped by the lateral sides outside the axis of the molecule. In the double or triple case, the p orbitals form one σ bond, and the rest will be of the π type.
Conjugation is the alternation of primes and multiples, making the molecule more stable. This property is characteristic of complex organic compounds.
Types and methods of formation of chemical bonds
Polarity
Important! How to determine whether substances with a non-polar covalent or polar bond are in front of us? This is very simple: the first always occurs between identical atoms, and the second - between different atoms that have unequal electronegativity.
Examples of covalent nonpolar bonds - simple substances:
- hydrogen H 2;
- nitrogen N2;
- oxygen O 2;
- chlorine Cl2.
The formation scheme of a covalent nonpolar bond shows that by combining an electron pair, atoms tend to complement the outer shell to 8 or 2 electrons. For example, fluorine is one electron short of an eight-electron shell. After the formation of the shared electron pair, it will be filled. The common formula for a substance with a covalent nonpolar bond is a diatomic molecule.
Polar usually only connect:
- H 2 O;
- CH4.
But there are exceptions, such as AlCl 3. Aluminum has the property of amphotericity, that is, in some compounds it behaves like a metal, and in others it behaves like a non-metal. The difference in electronegativity in this compound is small, so aluminum combines with chlorine in this way, and not according to the ionic type.
In this case, the molecule is formed by different elements, but the difference in electronegativity is not so great that the electron is completely transferred from one atom to another, as in substances with an ionic structure.
Schemes for the formation of this type of covalent structure show that the electron density shifts to a more electronegative atom, that is, the shared electron pair is closer to one of them than to the second. The parts of the molecule acquire a charge, which is denoted by the Greek letter delta. In hydrogen chloride, for example, the chlorine becomes more negatively charged and the hydrogen more positively charged. The charge will be partial, and not whole, like with ions.
Important! Bond polarity should not be confused with molecular polarity. In methane CH4, for example, the atoms are bonded polarly, but the molecule itself is nonpolar.
Useful video: polar and non-polar covalent bonds
Education mechanism
The formation of new substances can occur through an exchange or donor-acceptor mechanism. In this case, atomic orbitals are combined. One or more molecular orbitals arise. They differ in that they span both atoms. Like an atomic electron, it can contain no more than two electrons, and their spins must also be in different directions.
How to determine which mechanism is involved? This can be done by the number of electrons in the outer orbitals.
Exchange
In this case, an electron pair in a molecular orbital is formed from two unpaired electrons, each of which belongs to its own atom. Each of them strives to fill its outer electron shell and make it stable eight- or two-electron. This is how substances with a non-polar structure are usually formed.
For example, consider hydrochloric acid HCl. Hydrogen has one electron in its outer level. Chlorine has seven. Having drawn diagrams of the formation of a covalent structure for it, we will see that each of them lacks one electron to fill the outer shell. By sharing an electron pair among themselves, they will be able to complete the outer shell. The same principle is used to form diatomic molecules of simple substances, for example, hydrogen, oxygen, chlorine, nitrogen and other non-metals.
Education mechanism
Donor-acceptor
In the second case, both electrons are a lone pair and belong to the same atom (donor). The other (acceptor) has an empty orbital.
The formula of a substance with a covalent polar bond formed in this way, for example, ammonium ion NH 4 +. It is formed from a hydrogen ion, which has an empty orbital, and ammonia NH3, which contains one “extra” electron. The electron pair from ammonia is socialized.
Hybridization
When an electron pair is shared between orbitals of different shapes, such as s and p, a hybrid sp electron cloud is formed. Such orbitals overlap more, so they bind more tightly.
This is how the molecules of methane and ammonia are structured. In the CH 4 methane molecule, three bonds should have been formed in p-orbitals and one in s. Instead, the orbital hybridizes with three p orbitals, resulting in three sp3 hybrid orbitals in the shape of elongated droplets. This happens because the 2s and 2p electrons have similar energies, they interact with each other when they combine with another atom. Then a hybrid orbital can be formed. The resulting molecule has the shape of a tetrahedron, with hydrogen located at its vertices.
Other examples of substances with hybridization:
- acetylene;
- benzene;
- diamond;
- water.
Carbon is characterized by sp3 hybridization, so it is often found in organic compounds.
Useful video: polar covalent bond
Conclusion
A covalent bond, polar or nonpolar, is characteristic of substances with a molecular structure. Atoms of one element are nonpolarly bonded, while atoms of different elements are polarly bonded, but with slightly different electronegativity. Usually non-metallic elements are connected in this way, but there are exceptions, such as aluminum.
Covalent bond formed by the interaction of nonmetals. Nonmetal atoms have high electronegativity and tend to fill the outer electron layer with foreign electrons. Two such atoms can go into a stable state if they combine their electrons .
Let us consider the formation of a covalent bond in simple substances.
1.Formation of a hydrogen molecule.
Every atom hydrogen has one electron. To transition to a stable state, it needs one more electron.
When two atoms come close, the electron clouds overlap. A shared electron pair is formed, which bonds the hydrogen atoms into a molecule.
The space between two nuclei shares more electrons than other places. An area with increased electron density and negative charge. Positively charged nuclei are attracted to it, and a molecule is formed.
In this case, each atom receives a completed two-electron outer level and goes into a stable state.
A covalent bond due to the formation of one shared electron pair is called single.
Shared electron pairs (covalent bonds) are formed due to unpaired electrons, located on the outer energy levels of interacting atoms.
Hydrogen has one unpaired electron. For other elements, their number is 8 - group number.
Nonmetals VII And groups (halogens) have one unpaired electron on the outer layer.
In non-metals VI A groups (oxygen, sulfur) have two such electrons.
In non-metals V And groups (nitrogen, phosphorus) have three unpaired electrons.
2.Formation of a fluorine molecule.
Atom fluoride has seven electrons in the outer level. Six of them form pairs, and the seventh is unpaired.
When atoms join, one common electron pair is formed, that is, one covalent bond occurs. Each atom receives a completed eight-electron outer layer. The bond in the fluorine molecule is also single. The same single bonds exist in molecules chlorine, bromine and iodine .
If atoms have several unpaired electrons, then two or three common pairs are formed.
3.Formation of an oxygen molecule.
At the atom oxygen at the outer level there are two unpaired electrons.
When two atoms interact oxygen two common electron pairs arise. Each atom fills its outer level with up to eight electrons. The oxygen molecule has a double bond.
Not the least important role at the chemical level of the organization of the world is played by the way of connecting structural particles and connecting with each other. The overwhelming majority of simple substances, namely nonmetals, have a covalent nonpolar type of bond, with the exception of metals in their pure form, which have a special method of bonding, which is realized through the sharing of free electrons in the crystal lattice.
The types and examples of which will be indicated below, or more precisely, the localization or partial displacement of these bonds to one of the binding participants is explained precisely by the electronegative characteristic of a particular element. The displacement occurs towards the atom for which it is stronger.
Covalent nonpolar bond
The “formula” of a covalent nonpolar bond is simple - two atoms of the same nature combine the electrons of their valence shells into a joint pair. Such a pair is called divided because it belongs equally to both participants in the binding. It is thanks to the socialization of electron density in the form of a pair of electrons that atoms move into a more stable state, since they complete their outer electronic level, and the “octet” (or “doublet” in the case of the simple substance hydrogen H 2, it has a single s-orbital, for which requires two electrons to complete) is the state of the outer level to which all atoms tend, since its filling corresponds to the state with minimal energy.
An example of a non-polar covalent bond is found in inorganics and, no matter how strange it may sound, in organic chemistry too. This type of bond is inherent in all simple substances - non-metals, except for noble gases, since the valence level of an inert gas atom is already completed and has an octet of electrons, which means that bonding with a similar one does not make sense for it and is even less energetically beneficial. In organics, nonpolarity occurs in individual molecules of a certain structure and is conditional.
Covalent polar bond
The example of a nonpolar covalent bond is limited to a few molecules of a simple substance, while dipole compounds, in which the electron density is partially shifted towards the more electronegative element, are the vast majority. Any combination of atoms with different electronegativity gives a polar bond. In particular, the bonds in organics are polar covalent bonds. Sometimes ionic, inorganic oxides are also polar, and in salts and acids the ionic type of binding predominates.
The ionic type of compounds is sometimes considered as an extreme case of polar binding. If the electronegativity of one of the elements is significantly higher than that of the other, the electron pair is completely shifted from the bond center to it. This is how separation into ions occurs. The one who takes away an electron pair turns into an anion and receives a negative charge, and the one who loses an electron turns into a cation and becomes positive.
Examples of inorganic substances with a covalent nonpolar type of bond
Substances with a covalent nonpolar bond are, for example, all binary gas molecules: hydrogen (H - H), oxygen (O = O), nitrogen (in its molecule 2 atoms are connected by a triple bond (N ≡ N)); liquids and solids: chlorine (Cl - Cl), fluorine (F - F), bromine (Br - Br), iodine (I - I). And also complex substances consisting of atoms of different elements, but with virtually the same electronegativity value, for example, phosphorus hydride - PH 3.
Organics and non-polar binding
It is very clear that everything is complex. The question arises: how can there be a nonpolar bond in a complex substance? The answer is quite simple if you think about it a little logically. If the electronegativity values of bonded elements differ slightly and do not form a compound, such a bond can be considered non-polar. This is exactly the situation with carbon and hydrogen: all C - H bonds in organic matter are considered non-polar.
An example of a non-polar covalent bond is the simplest methane molecule. It consists of one carbon atom, which, according to its valence, is linked by single bonds to four hydrogen atoms. In fact, the molecule is not a dipole, since there is no localization of charges in it, somewhat due to its tetrahedral structure. The electron density is evenly distributed.
An example of a nonpolar covalent bond occurs in more complex organic compounds. It is realized due to mesomeric effects, that is, the sequential withdrawal of electron density, which quickly fades along the carbon chain. Thus, in a hexachloroethane molecule, the C - C bond is nonpolar due to the uniform withdrawal of electron density by six chlorine atoms.
Other types of connections
In addition to covalent bonds, which, by the way, can also occur through the donor-acceptor mechanism, there are ionic, metallic and hydrogen bonds. Brief characteristics of the penultimate two are presented above.
A hydrogen bond is an intermolecular electrostatic interaction that is observed if the molecule contains a hydrogen atom and any other atom that has lone electron pairs. This type of binding is much weaker than the others, but due to the fact that a lot of these bonds can be formed in the substance, it makes a significant contribution to the properties of the compound.
Covalent bond(atomic bond, homeopolar bond) - a chemical bond formed by the overlap (socialization) of paravalent electron clouds. The electronic clouds (electrons) that provide communication are called shared electron pair.
The characteristic properties of a covalent bond - directionality, saturation, polarity, polarizability - determine the chemical and physical properties of compounds.
The direction of the connection is determined by the molecular structure of the substance and the geometric shape of its molecule. The angles between two bonds are called bond angles.
Saturability is the ability of atoms to form a limited number of covalent bonds. The number of bonds formed by an atom is limited by the number of its outer atomic orbitals.
The polarity of the bond is due to the uneven distribution of electron density due to differences in the electronegativity of the atoms. On this basis, covalent bonds are divided into non-polar and polar (non-polar - a diatomic molecule consists of identical atoms (H 2, Cl 2, N 2) and the electron clouds of each atom are distributed symmetrically relative to these atoms; polar - a diatomic molecule consists of atoms of different chemical elements , and the general electron cloud shifts towards one of the atoms, thereby forming an asymmetry in the distribution of electric charge in the molecule, generating a dipole moment of the molecule).
The polarizability of a bond is expressed in the displacement of the bond electrons under the influence of an external electric field, including that of another reacting particle. Polarizability is determined by electron mobility. The polarity and polarizability of covalent bonds determines the reactivity of molecules towards polar reagents.
Education Communications
A covalent bond is formed by a pair of electrons shared between two atoms, and these electrons must occupy two stable orbitals, one from each atom.
A + + B → A: B
As a result of socialization, electrons form a filled energy level. A bond is formed if their total energy at this level is less than in the initial state (and the difference in energy will be nothing more than the bond energy).
Filling of atomic (along the edges) and molecular (in the center) orbitals in the H 2 molecule with electrons. The vertical axis corresponds to the energy level, electrons are indicated by arrows reflecting their spins.
According to the theory of molecular orbitals, the overlap of two atomic orbitals leads, in the simplest case, to the formation of two molecular orbitals (MO): linking MO And anti-binding (loosening) MO. The shared electrons are located on the lower energy bonding MO.
Types of covalent bond
There are three types of covalent chemical bonds, differing in the mechanism of formation:
1. Simple covalent bond. For its formation, each atom provides one unpaired electron. When a simple covalent bond is formed, the formal charges of the atoms remain unchanged.
· If the atoms forming a simple covalent bond are the same, then the true charges of the atoms in the molecule are also the same, since the atoms forming the bond equally own a shared electron pair. This connection is called non-polar covalent bond. Simple substances have such a connection, for example: O 2, N 2, Cl 2. But not only nonmetals of the same type can form a covalent nonpolar bond. Non-metal elements whose electronegativity is of equal importance can also form a covalent nonpolar bond, for example, in the PH 3 molecule the bond is covalent nonpolar, since the EO of hydrogen is equal to the EO of phosphorus.
· If the atoms are different, then the degree of possession of a shared pair of electrons is determined by the difference in the electronegativity of the atoms. An atom with greater electronegativity attracts a pair of bonding electrons more strongly toward itself, and its true charge becomes negative. An atom with lower electronegativity acquires, accordingly, a positive charge of the same magnitude. If a compound is formed between two different non-metals, then such a compound is called covalent polar bond.
2. Donor-acceptor bond. To form this type of covalent bond, both electrons are provided by one of the atoms - donor. The second of the atoms involved in the formation of a bond is called acceptor. In the resulting molecule, the formal charge of the donor increases by one, and the formal charge of the acceptor decreases by one.
3. Semipolar connection. It can be considered as a polar donor-acceptor bond. This type of covalent bond is formed between an atom with a lone pair of electrons (nitrogen, phosphorus, sulfur, halogens, etc.) and an atom with two unpaired electrons (oxygen, sulfur). The formation of a semipolar bond occurs in two stages:
1. Transfer of one electron from an atom with a lone pair of electrons to an atom with two unpaired electrons. As a result, an atom with a lone pair of electrons turns into a radical cation (a positively charged particle with an unpaired electron), and an atom with two unpaired electrons turns into a radical anion (a negatively charged particle with an unpaired electron).
2. Sharing of unpaired electrons (as in the case of a simple covalent bond).
When a semipolar bond is formed, an atom with a lone pair of electrons increases its formal charge by one, and an atom with two unpaired electrons decreases its formal charge by one.
σ bond and π bond
Sigma (σ)-, pi (π)-bonds are an approximate description of the types of covalent bonds in molecules of various compounds; the σ-bond is characterized by the fact that the density of the electron cloud is maximum along the axis connecting the nuclei of atoms. When a -bond is formed, the so-called lateral overlap of electron clouds occurs, and the density of the electron cloud is maximum “above” and “below” the σ-bond plane. For example, let's take ethylene, acetylene and benzene.
In the ethylene molecule C 2 H 4 there is a double bond CH 2 = CH 2, its electronic formula: H:C::C:H. The nuclei of all ethylene atoms are located in the same plane. The three electron clouds of each carbon atom form three covalent bonds with other atoms in the same plane (with angles between them of approximately 120°). The cloud of the fourth valence electron of the carbon atom is located above and below the plane of the molecule. Such electron clouds of both carbon atoms, partially overlapping above and below the plane of the molecule, form a second bond between the carbon atoms. The first, stronger covalent bond between carbon atoms is called a σ bond; the second, less strong covalent bond is called an -bond.
In a linear acetylene molecule
N-S≡S-N (N: S::: S: N)
There are σ bonds between carbon and hydrogen atoms, one σ bond between two carbon atoms, and two σ bonds between the same carbon atoms. Two -bonds are located above the sphere of action of the σ-bond in two mutually perpendicular planes.
All six carbon atoms of the cyclic benzene molecule C 6 H 6 lie in the same plane. There are σ bonds between carbon atoms in the plane of the ring; Each carbon atom has the same bonds with hydrogen atoms. Carbon atoms spend three electrons to make these bonds. Clouds of fourth valence electrons of carbon atoms, shaped like figures of eight, are located perpendicular to the plane of the benzene molecule. Each such cloud overlaps equally with the electron clouds of neighboring carbon atoms. In a benzene molecule, not three separate -bonds are formed, but a single -electronic system of six electrons, common to all carbon atoms. The bonds between the carbon atoms in the benzene molecule are exactly the same.
Examples of substances with covalent bonds
A simple covalent bond connects atoms in the molecules of simple gases (H 2, Cl 2, etc.) and compounds (H 2 O, NH 3, CH 4, CO 2, HCl, etc.). Compounds with a donor-acceptor bond - ammonium NH 4 +, tetrafluoroborate anion BF 4 - and others. Compounds with a semipolar bond - nitrous oxide N 2 O, O - -PCl 3 +.
Crystals with covalent bonds are dielectrics or semiconductors. Typical examples of atomic crystals (atoms in which are interconnected by covalent (atomic) bonds are diamond, germanium and silicon.
The only substance known to man with an example of a covalent bond between a metal and a carbon is cyanocobalamin, known as vitamin B12.
Ionic bond- a very strong chemical bond formed between atoms with a large difference (> 1.5 on the Pauling scale) of electronegativity, in which the common electron pair is completely transferred to an atom with greater electronegativity. This is the attraction of ions as oppositely charged bodies. An example is the compound CsF, in which the “degree of ionicity” is 97%. Let's consider the method of formation using sodium chloride NaCl as an example. The electronic configuration of sodium and chlorine atoms can be represented as: 11 Na 1s2 2s2 2p 6 3s1; 17 Cl 1s2 2s2 2p6 3s2 3р5. These are atoms with incomplete energy levels. Obviously, to complete them, it is easier for a sodium atom to give up one electron than to gain seven, and for a chlorine atom it is easier to gain one electron than to give up seven. During a chemical interaction, the sodium atom completely gives up one electron, and the chlorine atom accepts it. Schematically, this can be written as follows: Na. - l e -> Na+ sodium ion, stable eight-electron 1s2 2s2 2p6 shell due to the second energy level. :Cl + 1е --> .Cl - chlorine ion, stable eight electron shell. Electrostatic attraction forces arise between the Na+ and Cl- ions, resulting in the formation of a compound. Ionic bonding is an extreme case of polarization of a polar covalent bond. Formed between a typical metal and non-metal. In this case, the electrons from the metal are completely transferred to the non-metal. Ions are formed.
If a chemical bond is formed between atoms that have a very large difference in electronegativity (EO > 1.7 according to Pauling), then the common electron pair is completely transferred to the atom with a higher EO. The result of this is the formation of a compound of oppositely charged ions:
An electrostatic attraction occurs between the resulting ions, which is called ionic bonding. Or rather, this look is convenient. In fact, the ionic bond between atoms in its pure form is not realized anywhere or almost nowhere; usually, in fact, the bond is partly ionic and partly covalent in nature. At the same time, the bonding of complex molecular ions can often be considered purely ionic. The most important differences between ionic bonds and other types of chemical bonds are non-directionality and non-saturation. That is why crystals formed due to ionic bonds gravitate towards various dense packings of the corresponding ions.
Characteristics Such compounds have good solubility in polar solvents (water, acids, etc.). This occurs due to the charged parts of the molecule. In this case, the dipoles of the solvent are attracted to the charged ends of the molecule, and, as a result of Brownian motion, they “tear” the molecule of the substance into pieces and surround them, preventing them from connecting again. The result is ions surrounded by solvent dipoles.
When such compounds are dissolved, energy is usually released, since the total energy of the formed solvent-ion bonds is greater than the energy of the anion-cation bond. Exceptions are many salts of nitric acid (nitrates), which absorb heat when dissolved (solutions cool). The latter fact is explained on the basis of laws that are considered in physical chemistry.