Co chemical formula covalent bond. What is the term "polar"? §2 Chemical bond

A chemical bond is the interaction of particles (ions or atoms), which is carried out in the process of exchanging electrons located at the last electronic level. There are several types of such a bond: covalent (it is divided into non-polar and polar) and ionic. In this article, we will dwell in more detail on the first type of chemical bonds - covalent. And to be more precise, in its polar form.

A covalent polar bond is a chemical bond between the valence electron clouds of neighboring atoms. The prefix "ko-" - means in this case "together", and the basis of "valence" is translated as strength or ability. Those two electrons that bond with each other are called an electron pair.

Story

The term was first used in a scientific context by Nobel Prize-winning chemist Irving Lenngryum. It happened in 1919. In his work, the scientist explained that the bond in which electrons common to two atoms are observed differs from metallic or ionic. So, it requires a separate name.

Later, already in 1927, F. London and W. Heitler, taking as an example the hydrogen molecule as the chemically and physically simplest model, described a covalent bond. They got down to business from the other end, and substantiated their observations using quantum mechanics.

The essence of the reaction

The process of converting atomic hydrogen into molecular hydrogen is a typical chemical reaction, the qualitative feature of which is a large release of heat when two electrons combine. It looks something like this: two helium atoms are approaching each other, having one electron in their orbit. Then these two clouds approach each other and form a new one, similar to a helium shell, in which two electrons already rotate.

Completed electron shells are more stable than incomplete ones, so their energy is significantly lower than that of two separate atoms. During the formation of a molecule, excess heat is dissipated in the environment.

Classification

In chemistry, there are two types of covalent bonds:

A non-polar covalent bond formed between two atoms of the same non-metallic element, such as oxygen, hydrogen, nitrogen, carbon.
A covalent polar bond occurs between atoms of different non-metals. good example can serve as a molecule of hydrogen chloride. When atoms of two elements combine with each other, the unpaired electron from hydrogen partially passes to the last electronic level of the chlorine atom. Thus, a positive charge is formed on the hydrogen atom, and a negative charge on the chlorine atom.

Donor-acceptor bond is also a type of covalent bond. It consists in the fact that one atom from a pair provides both electrons, becoming a donor, and the atom accepting them, respectively, is considered an acceptor. When a bond is formed between atoms, the charge of the donor increases by one, and the charge of the acceptor decreases.

Semipolar bond - e It can be considered a subspecies of donor-acceptor. Only in this case, atoms unite, one of which has a complete electron orbital (halogens, phosphorus, nitrogen), and the second has two unpaired electrons (oxygen). Communication is formed in two stages:

first, one electron is removed from the lone pair and joined to the unpaired ones;
the union of the remaining unpaired electrodes, that is, a covalent polar bond is formed.

Properties

A polar covalent bond has its own physiochemical properties such as directivity, saturation, polarity, polarizability. They determine the characteristics of the resulting molecules.

The direction of the bond depends on the future molecular structure of the resulting substance, namely on geometric shape, which is formed by two atoms upon attachment.

Saturation shows how many covalent bonds one atom of a substance can form. This number is limited by the number of outer atomic orbitals.

The polarity of the molecule arises because the electron cloud, formed from two different electrons, is uneven along its entire circumference. This is due to the difference in negative charge in each of them. It is this property that determines whether a bond is polar or non-polar. When two atoms of the same element combine, the electron cloud is symmetrical, which means that the bond is covalent non-polar. What if atoms come together different elements, then an asymmetric electron cloud is formed, the so-called dipole moment of the molecule.

Polarizability reflects how actively the electrons in a molecule are displaced under the action of external physical or chemical agents, such as electrical or magnetic field, other particles.

The last two properties of the resulting molecule determine its ability to react with other polar reagents.

Sigma bond and pi bond

The formation of these bonds depends on the distribution density of electrons in the electron cloud during the formation of the molecule.

The sigma bond is characterized by the presence of a dense accumulation of electrons along the axis connecting the nuclei of atoms, that is, in the horizontal plane.

The pi bond is characterized by the compaction of electron clouds at the point of their intersection, that is, above and below the nucleus of an atom.

Visualizing Relationships in a Formula Entry

Let's take the chlorine atom as an example. Its outer electronic level contains seven electrons. In the formula, they are arranged in three pairs and one unpaired electron around the designation of the element in the form of dots.

If the chlorine molecule is written in the same way, it will be seen that two unpaired electrons have formed a pair common to two atoms, it is called shared. In addition, each of them received eight electrons.

Octet-Doublet Rule

The chemist Lewis, who proposed how a polar covalent bond is formed, was the first of his colleagues to formulate a rule explaining the stability of atoms when they are combined into molecules. Its essence lies in the fact that chemical bonds between atoms are formed when a sufficient number of electrons are socialized to obtain an electronic configuration that repeats similar to the atoms of noble elements.

That is, when molecules are formed, for their stabilization it is necessary that all atoms have a complete external electronic level. For example, hydrogen atoms, uniting into a molecule, repeat the electron shell of helium, chlorine atoms, acquire similarity at the electronic level with the argon atom.

Link length

A covalent polar bond, among other things, is characterized by a certain distance between the nuclei of the atoms that form the molecule. They are located at such a distance from each other at which the energy of the molecule is minimal. In order to achieve this, it is necessary that the electron clouds of atoms overlap each other as much as possible. There is a directly proportional pattern between the size of the atoms and the long bond. The larger the atom, the longer the bond between the nuclei.

A variant is possible when an atom forms not one, but several covalent polar bonds. Then the so-called valence angles are formed between the nuclei. They can be from ninety to one hundred and eighty degrees. They determine the geometric formula of the molecule.

Topics of the USE codifier: Covalent chemical bond, its varieties and mechanisms of formation. Characteristics of a covalent bond (polarity and bond energy). Ionic bond. metal connection. hydrogen bond

Intramolecular chemical bonds

Let us first consider the bonds that arise between particles within molecules. Such connections are called intramolecular.

chemical bond between atoms of chemical elements has an electrostatic nature and is formed due to interactions of external (valence) electrons, in more or less degree held by positively charged nuclei bonded atoms.

The key concept here is ELECTRONEGNATIVITY. It is she who determines the type of chemical bond between atoms and the properties of this bond.

is the ability of an atom to attract (hold) external(valence) electrons. Electronegativity is determined by the degree of attraction outer electrons to the nucleus and depends mainly on the radius of the atom and the charge of the nucleus.

Electronegativity is difficult to determine unambiguously. L. Pauling compiled a table of relative electronegativity (based on the bond energies of diatomic molecules). The most electronegative element is fluorine with meaning 4 .

It is important to note that in different sources you can find different scales and tables of electronegativity values. This should not be frightened, since the formation of a chemical bond plays a role atoms, and it is approximately the same in any system.

If one of the atoms in the chemical bond A:B attracts electrons more strongly, then the electron pair is shifted towards it. The more electronegativity difference atoms, the more the electron pair is displaced.

If the electronegativity values of the interacting atoms are equal or approximately equal: EO(A)≈EO(V), then the shared electron pair is not displaced to any of the atoms: A: B. Such a connection is called covalent non-polar.

If the electronegativity of the interacting atoms differ, but not much (the difference in electronegativity is approximately from 0.4 to 2: 0,4<ΔЭО<2 ), then the electron pair is shifted to one of the atoms. Such a connection is called covalent polar .

If the electronegativity of the interacting atoms differ significantly (the difference in electronegativity is greater than 2: ΔEO>2), then one of the electrons almost completely passes to another atom, with the formation ions. Such a connection is called ionic.

The main types of chemical bonds are − covalent, ionic and metallic connections. Let's consider them in more detail.

covalent chemical bond

covalent bond – it's a chemical bond formed by formation of a common electron pair A:B . In this case, two atoms overlap atomic orbitals. A covalent bond is formed by the interaction of atoms with a small difference in electronegativity (as a rule, between two non-metals) or atoms of one element.

Basic properties of covalent bonds

orientation,
saturability,
polarity,
polarizability.

These bond properties affect the chemical and physical properties of substances.

Direction of communication characterizes chemical structure and shape of substances. The angles between two bonds are called bond angles. For example, in a water molecule, the H-O-H bond angle is 104.45 o, so the water molecule is polar, and in the methane molecule, the H-C-H bond angle is 108 o 28 ′.

Saturability is the ability of atoms to form a limited number of covalent chemical bonds. The number of bonds that an atom can form is called.

Polarity bonds arise due to the uneven distribution of electron density between two atoms with different electronegativity. Covalent bonds are divided into polar and non-polar.

Polarizability connections are the ability of bond electrons to be displaced by an external electric field(in particular, the electric field of another particle). The polarizability depends on the electron mobility. The farther the electron is from the nucleus, the more mobile it is, and, accordingly, the molecule is more polarizable.

Covalent non-polar chemical bond

There are 2 types of covalent bonding - POLAR and NON-POLAR .

Example . Consider the structure of the hydrogen molecule H 2 . Each hydrogen atom carries 1 unpaired electron in its outer energy level. To display an atom, we use the Lewis structure - this is a diagram of the structure of the external energy level of an atom, when electrons are denoted by dots. Lewis point structure models are a good help when working with elements of the second period.

H. + . H=H:H

Thus, the hydrogen molecule has one common electron pair and one H–H chemical bond. This electron pair is not displaced to any of the hydrogen atoms, because the electronegativity of hydrogen atoms is the same. Such a connection is called covalent non-polar .

Covalent non-polar (symmetrical) bond - this is a covalent bond formed by atoms with equal electronegativity (as a rule, the same non-metals) and, therefore, with a uniform distribution of electron density between the nuclei of atoms.

The dipole moment of nonpolar bonds is 0.

Examples: H 2 (H-H), O 2 (O=O), S 8 .

Covalent polar chemical bond

covalent polar bond is a covalent bond that occurs between atoms with different electronegativity (usually, different non-metals) and is characterized displacement common electron pair to a more electronegative atom (polarization).

The electron density is shifted to a more electronegative atom - therefore, a partial negative charge (δ-) appears on it, and a partial positive charge appears on a less electronegative atom (δ+, delta +).

The greater the difference in the electronegativity of atoms, the higher polarity connections and even more dipole moment . Between neighboring molecules and charges opposite in sign, additional attractive forces act, which increases strength connections.

Bond polarity affects the physical and chemical properties of compounds. The reaction mechanisms and even the reactivity of neighboring bonds depend on the polarity of the bond. The polarity of a bond often determines polarity of the molecule and thus directly affects such physical properties as boiling point and melting point, solubility in polar solvents.

Examples: HCl, CO 2 , NH 3 .

Mechanisms for the formation of a covalent bond

A covalent chemical bond can occur by 2 mechanisms:

1. exchange mechanism the formation of a covalent chemical bond is when each particle provides one unpaired electron for the formation of a common electron pair:

BUT . + . B= A:B

2. The formation of a covalent bond is such a mechanism in which one of the particles provides an unshared electron pair, and the other particle provides a vacant orbital for this electron pair:

BUT: + B= A:B

In this case, one of the atoms provides an unshared electron pair ( donor), and the other atom provides a vacant orbital for this pair ( acceptor). As a result of the formation of a bond, both electron energy decreases, i.e. this is beneficial for the atoms.

A covalent bond formed by the donor-acceptor mechanism, is not different by properties from other covalent bonds formed by the exchange mechanism. The formation of a covalent bond by the donor-acceptor mechanism is typical for atoms either with a large number of electrons in the external energy level (electron donors), or vice versa, with a very small number of electrons (electron acceptors). The valence possibilities of atoms are considered in more detail in the corresponding.

A covalent bond is formed by the donor-acceptor mechanism:

- in a molecule carbon monoxide CO(the bond in the molecule is triple, 2 bonds are formed by the exchange mechanism, one by the donor-acceptor mechanism): C≡O;

- in ammonium ion NH 4 +, in ions organic amines, for example, in the methylammonium ion CH 3 -NH 2 + ;

- in complex compounds, a chemical bond between the central atom and groups of ligands, for example, in sodium tetrahydroxoaluminate Na the bond between aluminum and hydroxide ions;

- in nitric acid and its salts- nitrates: HNO 3 , NaNO 3 , in some other nitrogen compounds;

- in a molecule ozone O 3 .

Main characteristics of a covalent bond

A covalent bond, as a rule, is formed between the atoms of non-metals. The main characteristics of a covalent bond are length, energy, multiplicity and directivity.

Chemical bond multiplicity

Chemical bond multiplicity - this is the number of shared electron pairs between two atoms in a compound. The multiplicity of the bond can be quite easily determined from the value of the atoms that form the molecule.

For example , in the hydrogen molecule H 2 the bond multiplicity is 1, because each hydrogen has only 1 unpaired electron in the outer energy level, therefore, one common electron pair is formed.

In the oxygen molecule O 2, the bond multiplicity is 2, because each atom has 2 unpaired electrons in its outer energy level: O=O.

In the nitrogen molecule N 2, the bond multiplicity is 3, because between each atom there are 3 unpaired electrons in the outer energy level, and the atoms form 3 common electron pairs N≡N.

Covalent bond length

Chemical bond length is the distance between the centers of the nuclei of atoms that form a bond. It is determined by experimental physical methods. The bond length can be estimated approximately, according to the additivity rule, according to which the bond length in the AB molecule is approximately equal to half the sum of the bond lengths in the A 2 and B 2 molecules:

The length of a chemical bond can be roughly estimated along the radii of atoms, forming a bond, or by the multiplicity of communication if the radii of the atoms are not very different.

With an increase in the radii of the atoms forming a bond, the bond length will increase.

For example

With an increase in the multiplicity of bonds between atoms (whose atomic radii do not differ, or differ slightly), the bond length will decrease.

For example . In the series: C–C, C=C, C≡C, the bond length decreases.

Bond energy

A measure of the strength of a chemical bond is the bond energy. Bond energy is determined by the energy required to break the bond and remove the atoms that form this bond to an infinite distance from each other.

The covalent bond is very durable. Its energy ranges from several tens to several hundreds of kJ/mol. The greater the bond energy, the greater the bond strength, and vice versa.

The strength of a chemical bond depends on the bond length, bond polarity, and bond multiplicity. The longer the chemical bond, the easier it is to break, and the lower the bond energy, the lower its strength. The shorter the chemical bond, the stronger it is, and the greater the bond energy.

For example, in the series of compounds HF, HCl, HBr from left to right the strength of the chemical bond decreases, because the length of the bond increases.

Ionic chemical bond

Ionic bond is a chemical bond based on electrostatic attraction of ions.

ions are formed in the process of accepting or giving away electrons by atoms. For example, the atoms of all metals weakly hold the electrons of the outer energy level. Therefore, metal atoms are characterized restorative properties the ability to donate electrons.

Example. The sodium atom contains 1 electron at the 3rd energy level. Easily giving it away, the sodium atom forms a much more stable Na + ion, with the electron configuration of the noble neon gas Ne. The sodium ion contains 11 protons and only 10 electrons, so the total charge of the ion is -10+11 = +1:

+11Na) 2 ) 8 ) 1 - 1e = +11 Na +) 2 ) 8

Example. The chlorine atom has 7 electrons in its outer energy level. To acquire the configuration of a stable inert argon atom Ar, chlorine needs to attach 1 electron. After the attachment of an electron, a stable chlorine ion is formed, consisting of electrons. The total charge of the ion is -1:

+17Cl) 2 ) 8 ) 7 + 1e = +17 Cl — ) 2 ) 8 ) 8

Note:

The properties of ions are different from the properties of atoms!
Stable ions can form not only atoms, but also groups of atoms. For example: ammonium ion NH 4 +, sulfate ion SO 4 2-, etc. Chemical bonds formed by such ions are also considered ionic;
Ionic bonds are usually formed between metals and nonmetals(groups of non-metals);

The resulting ions are attracted due to electrical attraction: Na + Cl -, Na 2 + SO 4 2-.

Let us visually generalize difference between covalent and ionic bond types:

metal connection is the relationship that is formed relatively free electrons between metal ions forming a crystal lattice.

The atoms of metals on the outer energy level usually have one to three electrons. The radii of metal atoms, as a rule, are large - therefore, metal atoms, unlike non-metals, quite easily donate outer electrons, i.e. are strong reducing agents.

By donating electrons, metal atoms become positively charged ions . The detached electrons are relatively free are moving between positively charged metal ions. Between these particles there is a connection, because shared electrons hold metal cations in layers together , thus creating a sufficiently strong metal crystal lattice . In this case, the electrons continuously move randomly, i.e. new neutral atoms and new cations are constantly emerging.

Intermolecular interactions

Separately, it is worth considering the interactions that occur between individual molecules in a substance - intermolecular interactions . Intermolecular interactions are a type of interaction between neutral atoms in which new covalent bonds do not appear. The forces of interaction between molecules were discovered by van der Waals in 1869 and named after him. Van dar Waals forces. Van der Waals forces are divided into orientation, induction and dispersion . The energy of intermolecular interactions is much less than the energy of a chemical bond.

Orientation forces of attraction arise between polar molecules (dipole-dipole interaction). These forces arise between polar molecules. Inductive interactions is the interaction between a polar molecule and a non-polar one. A non-polar molecule is polarized due to the action of a polar one, which generates an additional electrostatic attraction.

A special type of intermolecular interaction is hydrogen bonds. - these are intermolecular (or intramolecular) chemical bonds that arise between molecules in which there are strongly polar covalent bonds - H-F, H-O or H-N. If there are such bonds in the molecule, then between the molecules there will be additional forces of attraction .

Mechanism of education The hydrogen bond is partly electrostatic and partly donor-acceptor. In this case, an atom of a strongly electronegative element (F, O, N) acts as an electron pair donor, and hydrogen atoms connected to these atoms act as an acceptor. Hydrogen bonds are characterized orientation in space and saturation .

The hydrogen bond can be denoted by dots: H ··· O. The greater the electronegativity of an atom connected to hydrogen, and the smaller its size, the stronger the hydrogen bond. It is primarily characteristic of compounds fluorine with hydrogen , as well as to oxygen with hydrogen , less nitrogen with hydrogen .

Hydrogen bonds occur between the following substances:

— hydrogen fluoride HF(gas, solution of hydrogen fluoride in water - hydrofluoric acid), water H 2 O (steam, ice, liquid water):

— solution of ammonia and organic amines- between ammonia and water molecules;

— organic compounds in which O-H or N-H bonds: alcohols, carboxylic acids, amines, amino acids, phenols, aniline and its derivatives, proteins, solutions of carbohydrates - monosaccharides and disaccharides.

The hydrogen bond affects the physical and chemical properties of substances. Thus, the additional attraction between molecules makes it difficult for substances to boil. Substances with hydrogen bonds exhibit an abnormal increase in the boiling point.

For example As a rule, with an increase in molecular weight, an increase in the boiling point of substances is observed. However, in a number of substances H 2 O-H 2 S-H 2 Se-H 2 Te we do not observe a linear change in boiling points.

Namely, at boiling point of water is abnormally high - not less than -61 o C, as the straight line shows us, but much more, +100 o C. This anomaly is explained by the presence of hydrogen bonds between water molecules. Therefore, under normal conditions (0-20 o C), water is liquid by phase state.

The covalent bond is carried out due to the socialization of electrons belonging to both atoms participating in the interaction. The electronegativities of non-metals are large enough that electron transfer does not occur.

Electrons in overlapping electron orbitals enter the common use. In this case, a situation is created in which the outer electronic levels of atoms are filled, that is, an 8- or 2-electron outer shell is formed.

The state in which the electron shell is completely filled is characterized by the lowest energy and, accordingly, the maximum stability.

There are two mechanisms of education:

donor-acceptor;
exchange.

In the first case, one of the atoms provides its pair of electrons, and the second - a free electron orbital.

In the second, one electron from each participant in the interaction comes to the common pair.

Depending on what type they are- atomic or molecular, compounds with a similar type of bond can vary significantly in physicochemical characteristics.

molecular substances most often gases, liquids or solids with low melting and boiling points, non-conductive, with low strength. These include: hydrogen (H 2), oxygen (O 2), nitrogen (N 2), chlorine (Cl 2), bromine (Br 2), rhombic sulfur (S 8), white phosphorus (P 4) and others simple substances; carbon dioxide (CO 2), sulfur dioxide (SO 2), nitric oxide V (N 2 O 5), water (H 2 O), hydrogen chloride (HCl), hydrogen fluoride (HF), ammonia (NH 3), methane (CH 4), ethyl alcohol (C 2 H 5 OH), organic polymers and others.

Substances atomic exist in the form of strong crystals with high boiling and melting points, are insoluble in water and other solvents, many do not conduct electric current. An example is a diamond, which has exceptional strength. This is due to the fact that diamond is a crystal consisting of carbon atoms connected by covalent bonds. There are no individual molecules in a diamond. Substances such as graphite, silicon (Si), silicon dioxide (SiO 2), silicon carbide (SiC) and others also have an atomic structure.

Covalent bonds can be not only single (as in the Cl2 chlorine molecule), but also double, as in the O2 oxygen molecule, or triple, as, for example, in the N2 nitrogen molecule. At the same time, triple ones have more energy and are more durable than double and single ones.

The covalent bond can be It is formed both between two atoms of the same element (non-polar) and between atoms of different chemical elements (polar).

It is not difficult to indicate the formula of a compound with a covalent polar bond if we compare the values of the electronegativity that make up the molecules of atoms. The absence of a difference in electronegativity will determine non-polarity. If there is a difference, then the molecule will be polar.

Don't Miss: Mechanism of Education, Case Studies.

Covalent non-polar chemical bond

Typical for simple substances non-metals. The electrons belong to the atoms equally, and there is no displacement of the electron density.

The following molecules are examples:

H2, O2, O3, N2, F2, Cl2.

Exceptions are inert gases. Their external energy level is completely filled, and the formation of molecules is energetically unfavorable for them, and therefore they exist in the form of separate atoms.

Also, an example of substances with a non-polar covalent bond would be, for example, PH3. Despite the fact that the substance consists of different elements, the values of the electronegativity of the elements do not actually differ, which means that there will be no displacement of the electron pair.

Covalent polar chemical bond

Considering the covalent polar bond, there are many examples: HCl, H2O, H2S, NH3, CH4, CO2, SO3, CCl4, SiO2, CO.

formed between atoms of non-metals with different electronegativity. In this case, the nucleus of an element with greater electronegativity attracts common electrons closer to itself.

Scheme of the formation of a covalent polar bond

Depending on the mechanism of formation, common can become electrons of one or both atoms.

The picture clearly shows the interaction in the hydrochloric acid molecule.

A pair of electrons belongs to both one atom and the second, both of them, so the outer levels are filled. But more electronegative chlorine attracts a pair of electrons a little closer to itself (while it remains common). The difference in electronegativity is not large enough for a pair of electrons to pass to one of the atoms completely. The result is a partial negative charge for chlorine and a partial positive charge for hydrogen. The HCl molecule is a polar molecule.

Physical and chemical properties of the bond

Communication can be characterized by the following properties: directivity, polarity, polarizability and saturation.

Definition

A covalent bond is a chemical bond formed due to the socialization of atoms of their valence electrons. An obligatory condition for the formation of a covalent bond is the overlap of atomic orbitals (AO), on which valence electrons are located. In the simplest case, the overlap of two AOs leads to the formation of two molecular orbitals (MOs): a bonding MO and an antibonding (loosening) MO. Shared electrons are located on a lower energy binding MO:

Communication education

Covalent bond (atomic bond, homeopolar bond) - a bond between two atoms due to the socialization (electron sharing) of two electrons - one from each atom:

A. + B. -> A: B

For this reason, the homeopolar relationship has a directional character. A pair of electrons making a bond belongs simultaneously to both bonding atoms, for example:

	..		..				..
:	Cl	:	Cl	:	H	:	O	:	H
	..		..				..

Types of covalent bond

There are three types of covalent chemical bonds that differ in the mechanism of their formation:

1. Simple covalent bond. For its formation, each of the atoms 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 socialized electron pair, such a bond is called a non-polar covalent bond. If the atoms are different, then the degree of ownership of a socialized pair of electrons is determined by the difference in the electronegativity of the atoms, an atom with a greater electronegativity has a pair of bond electrons to a greater extent, and therefore its true charge has negative sign, an atom with a lower electronegativity acquires, respectively, the same charge, but with a positive sign.

Sigma (σ)-, pi (π)-bonds - an approximate description of the types of covalent bonds in the molecules of organic compounds, 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 π-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 plane of the σ-bond. For example, take ethylene, acetylene and benzene.

In the ethylene molecule C 2 H 4 there is a double bond CH 2 \u003d CH 2, its electronic formula is: H: C:: C: H. The nuclei of all ethylene atoms are located in the same plane. Three electron clouds of each carbon atom form three covalent bonds with other atoms in the same plane (with angles between them of about 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 carbon atoms. The first, stronger covalent bond between carbon atoms is called a σ-bond; the second, less strong covalent bond is called a π-bond.

In a linear acetylene molecule

H-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 π-bonds between the same carbon atoms. Two π-bonds are located above the sphere of action of the σ-bond in two mutually perpendicular planes.

All six carbon atoms of the C 6 H 6 cyclic benzene molecule lie in the same plane. σ-bonds act between carbon atoms in the plane of the ring; the same bonds exist for each carbon atom with hydrogen atoms. Each carbon atom spends three electrons to make these bonds. Clouds of the fourth valence electrons of carbon atoms, having the shape of eights, are located perpendicular to the plane of the benzene molecule. Each such cloud overlaps equally with the electron clouds of neighboring carbon atoms. In the benzene molecule, not three separate π-bonds are formed, but a single π-electron system of six electrons, common to all carbon atoms. The bonds between the carbon atoms in the benzene molecule are exactly the same.

A covalent bond is formed as a result of the socialization of electrons (with the formation of common electron pairs), which occurs during the overlap of electron clouds. Electron clouds of two atoms participate in the formation of a covalent bond. There are two main types of covalent bonds:

A covalent non-polar bond is formed between non-metal atoms of the same chemical element. Simple substances have such a bond, for example, O 2; N 2 ; C 12 .
A covalent polar bond is formed between atoms of different non-metals.

Literature

"Chemical Encyclopedic Dictionary", M., " Soviet Encyclopedia", 1983, p.264.

Organic chemistry

List of organic compounds

Structural chemistry
Chemical bond:	Aromaticity \| covalent bond\| Ionic bond \| Metal connection \| Hydrogen bond \| Donor-acceptor bond \| Tautomerism
Structure display:	Functional group \| Structural formula \| Chemical formula \| ligand
Electronic properties:	Electronegativity \| Electron affinity \| Ionization energy \| Dipole \| Octet Rule
Stereochemistry:	Asymmetric atom \| Isomerism \| Configuration \| Chirality \| Conformation

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CHEMICAL BOND The mechanism by which atoms combine to form molecules. There are several types of such a bond, based either on the attraction of opposite charges, or on the formation of stable configurations through the exchange of electrons. ... ... Scientific and technical encyclopedic dictionary

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Mutual attraction of atoms, leading to the formation of molecules and crystals. It is customary to say that in a molecule or in a crystal between neighboring atoms there are ch. The valence of an atom (which is discussed in more detail below) indicates the number of bonds ... Great Soviet Encyclopedia

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An ionic bond is a strong chemical bond formed between atoms with a large difference in electronegativity, in which the common electron pair is completely transferred to an atom with a greater electronegativity. An example is the CsF compound ... Wikipedia

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covalent bond(from the Latin "with" jointly and "vales" valid) is carried out by an electron pair belonging to both atoms. Formed between atoms of non-metals.

The electronegativity of non-metals is quite large, so that during the chemical interaction of two non-metal atoms, the complete transfer of electrons from one to the other (as in the case) is impossible. In this case, electron pooling is necessary to perform.

As an example, let's discuss the interaction of hydrogen and chlorine atoms:

H 1s 1 - one electron

Cl 1s 2 2s 2 2 p6 3 s2 3 p5 - seven electrons in the outer level

Each of the two atoms lacks one electron in order to have a complete outer electron shell. And each of the atoms allocates “for common use” one electron. Thus, the octet rule is satisfied. The best way to represent this is with the Lewis formulas:

Formation of a covalent bond

The shared electrons now belong to both atoms. The hydrogen atom has two electrons (its own and the shared electron of the chlorine atom), and the chlorine atom has eight electrons (its own plus the shared electron of the hydrogen atom). These two shared electrons form a covalent bond between the hydrogen and chlorine atoms. The particle formed when two atoms bond is called molecule.

Non-polar covalent bond

A covalent bond can form between two the same atoms. For example:

This diagram explains why hydrogen and chlorine exist as diatomic molecules. Thanks to the pairing and socialization of two electrons, it is possible to fulfill the octet rule for both atoms.

In addition to single bonds, a double or triple covalent bond can be formed, as, for example, in oxygen O 2 or nitrogen N 2 molecules. Nitrogen atoms each have five valence electrons, so three more electrons are required to complete the shell. This is achieved by sharing three pairs of electrons, as shown below:

Covalent compounds - usually gases, liquids, or relatively low melting points solids. One of the rare exceptions is diamond, which melts above 3,500°C. This is due to 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 join together. The resulting structure is called a molecule.

Polar covalent bond

In most cases, two covalently bonded atoms have different electronegativity and shared electrons do not belong equally to two atoms. Most of the time they are closer to one atom than to another. In a molecule of hydrogen chloride, for example, the electrons that form a covalent bond are located closer to the chlorine atom, since its electronegativity is higher than that of hydrogen. However, the difference in the ability to attract electrons is not so great that there is a complete transfer of an electron from a hydrogen atom to a chlorine atom. Therefore, the bond between hydrogen and chlorine atoms can be viewed as a cross between an ionic bond (full electron transfer) and a non-polar covalent bond (symmetrical arrangement of a pair of electrons between two atoms). The partial charge on atoms is denoted by the Greek letter δ. Such a connection is called 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).