The mechanism of formation of multiple communication. Covalent Communication: Polar and non-polar, properties and examples. Communication formation during atomic recombination

Ks. - Communication carried out at the expense of an electronic pair belonging to both atoms.

Conditions for the formation of KS.: It is formed between atoms with high electronegitability. (Electootrotre - the ability of atoms to attract electrons to itself).

Δχ is the difference in electronegability of 2 atoms, if Δχ≤1.4, the connection is polar

CS M.B. Educated:

1 - Between any non-metal atoms (because all non-metals are high values \u200b\u200bof electrotrum), pr: hcl, the values \u200b\u200bof electrotrum - according to the tables, y n \u003d 2.1, cl \u003d 3.1, - δχ \u003d 3.1-2.1 \u003d 1≤1.4, this is a covalent and polar connection.

2 - between non-metal and metal atoms, if the metal is in a high oxidation, Pr: CRCl6 forcr \u003d 2.4, Δχ \u003d 3.1-2.4 \u003d 0.7≤1.4 is a covalent polar connection.

Mechanisms for the formation of KS.:

1 - oven mechanism - 2 atoms exchange electrons, forming a common electronic pair belonging to both and called "divided". An example is the molecules of volatile inorganic compounds: NSL, H 2 O, H 2 S, NN 3, etc. The formation of the HCl molecule can be represented by N. + scheme. CL: \u003d N: CL: The electron pair is shifted to the chlorine atom, since the relative electronegability of the chlorine atom (2.83) is greater than the hydrogen atom (2,1).

2 - donor-acceptor mechanism: - It is that the pair of electrons of one atom (donor) occupies a free orbital of the other atom (acceptor), consider as an example the ammonium ion formation mechanism. In the ammonia molecule, the nitrogen atom has a watelling pair of electrons by a two-electron cloud) :.

The hydrogen ion is free (not filled) 1S-orbital, which can be denoted as □ H +. When forming an ammonium ion, a two-electronic cloud of nitrogen becomes common to atoms of nitrogen and hydrogen, i.e. It turns into a molecular electronic cloud. So, the fourth covalent bond arises. Ammonium ion formation process can be submitted by the scheme

+ □ H + →

The hydrogen ion charge becomes common (it is delocalized, i.e. dispersed between all atoms), and a two-electron cloud (a vapor electron pair) belonging to nitrogen becomes common with hydrogen.

Covalent communication It happens polar (complex molecules) and non-polar (simple molecules).

Covalent bond properties

Covalent Communication has a number of important properties. These include: satiety and focus.

Saturability - the characteristic property of a covalent bond. It manifests itself in the ability of atoms to form a limited number of covalent bonds. This is due to the fact that one atom orbital can take part in the formation of only one covalent chemical bond. This property determines the composition of molecular chemical compounds. So, when the interaction of hydrogen atoms, H 2 molecule is formed, and not H 3. The third hydrogen atom cannot join, since the spin of its electron will be a parallel back of one of the paired electrons in the molecule. The ability to form a certain number of covalent bonds in atoms of various elements is limited to obtaining the maximum number of unpaired valence electrons.

Food - The property of a covalent bond, which determines the geometric structure of the molecule. The cause of communication is that the overlap of electronic orbitals is possible only with their specific mutual orientation, which ensures the largest electron density in the field of overlapping. In this case, the most durable chemical communications.

A covalent bond is a connection that binds the most often atoms of non-metals of molecules and crystals. What a chemical connection is called covalent to speak this article.

What is a covalent chemical connection?

Covalent Chemical Communication is a connection carried out by the formation of general (binding) electronic pairs.

If there is one general electron pair between two atoms, then such a link is called single (ordinary), if two - double, if three are triple.

Communication is made to designate horizontal dash between atoms. For example, in a hydrogen molecule, single bond: h-H; in oxygen molecule double communication: O \u003d O; In nitrogen molecule Triple Communication:

Fig. 1. Triple relationship in the nitrogen molecule.

The higher the multiplicity of communication, the stronger the molecule: the presence of a triple relationship explains the high chemical stability of nitrogen molecules.

Education and types of covalent communications

There are two covalent communication mechanisms: a mechanism and a donor-acceptor mechanism:

• exchangeable mechanism. With the exchange mechanism for the formation of a general electron pair, two binding atoms provide one unpaired electron. This is how it happens, for example, when the hydrogen molecule is formed.

Fig. 2. The formation of hydrogen molecule.

The total electron pair belongs to each of the associated atoms, that is, electronic shell They have completed.

• donor-acceptor mechanism. With a donor-acceptor mechanism, a general electron pair represents one of the binding atoms, one that is more electronegative. The second atom represents a free orbital for a common electron pair.

Fig. 3. The formation of ammonium ion.

So the ion of ammonium NH 4 + is formed. This positively charged ion (cation) is formed by the interaction of ammonia gas with any acid. In a solution of acid, hydrogen cations (protons) exist, in the hydrogen medium forming hydroxony cation H 3 O +. Ammonia formula NH 3: The molecule consists of one nitrogen atom and three hydrogen atoms associated with single covalent bonds on the exchange mechanism. At the nitrogen atom, one marked electron pair remains. It provides it as general as a donor, hydrogen ion H + having a free orbital.

Covalent chemical connection in chemicals May be polar and non-polar. Communication does not have a dipole moment, that is, polarity, if two atoms of the same element are connected having the same electronegability value. So, in the molecule of hydrogen, the connection is notolar.

In the HCl chloride molecule, atoms with different electronegathy are connected by a covalent election bond. The general electron pair turns out to be shifted towards chlorine, which has the higher an electrone affinity and electronegativity. There is a dipole moment, the connection becomes polar. In this case, a partial separation of charge occurs: the hydrogen atom becomes the positive end of the dipole, and the chlorine atom is negative.

Any covalent bond has the following characteristics: Energy, length, multiplicity, polarity, polarizability, saturation, direction in space

What did we know?

Covalent chemical bond is formed by overlapping a pair of valence electronic clouds. This type of communication can be formed by a donor-acceptor mechanism, as well as an exchange mechanism. Covalent bond is polar and non-polar and characterized by the presence of length, multiplicity, polarity, direction in space.

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It is known that non-metals interact with each other. Consider the mechanism for the occurrence of covalent bond on the example of the formation of hydrogen molecule:
N + H \u003d H 2 H \u003d - 436kj / mole

Imagine that we have two separate isolated hydrogen atoms. The kernel of each of the free hydrogen atoms is surrounded by a spherical symmetric electronic cloud formed by 1S-electron (see Fig. 1). Under the rapprochement of atoms to a certain distance, partial overlapping of electronic shells (orbitals) occurs (Fig. 2).

As a result, a molecular two-electron cloud has a molecular two-electron cloud, which has a maximum electron density in the space between nuclei; An increase in the density of the negative charge favors a strong increase in the attraction forces between the nuclei and the molecular cloud.

So, a covalent bond is formed as a result of overlapping the electron clouds of atoms, accompanied by the release of energy. If the distance between the cores is 0.106 nm closest to the touch of the hydrogen atoms, then after overlapping the electron clouds (the formation of the H 2 molecule), this distance is 0.074 nm (Fig. 2).

Typically, the largest overlap of electronic clouds is carried out along the line connecting the kernel of two atoms.

Chemical bond is the stronger than the overlapping of electronic orbitals.

As a result of the occurrence of the chemical bond between the two hydrogen atoms, each of them reaches electronic configuration of the noble gas atom.

Picture chemical bonds are accepted in different ways:

1) using electrons in the form of points supplied from chemical sign element.

Then the formation of a hydrogen molecule can be shown by the scheme:
N + N N: n

2) using quantum cells (HUND cells), as the placement of two electrons with opposite spins in one molecular quantum cell:

The scheme located on the left shows that the molecular energy level is lower than the initial atomic levels, and therefore the molecular state of the substance is more stable than atomic.

3) often, especially in organic chemistry, covalent communication is depicted by a dash (stroke)

(for example, nn), which symbolizes a pair of electrons.
Covalent bond in the chlorine molecule is also carried out with the help of two common electrons, or an electronic pair:


As can be seen, each chlorine atom has three meaningless pairs and one unpaired electron.

The formation of chemical communications occurs due to unpaired electrons of each atom. Unpaired electrons are associated with a common pair of electrons, also called a common (divided) pair.

If one covalent bond arose between the atoms (one general electron pair), then it is called single; If more, then multiple (two common electronic pairs), triple (three general electronic pairs).

Single connection is depicted in one dash (stroke), double - two, triple - three. The dash between two atoms shows that they have a pair of electrons are generalized, as a result of which a chemical connection was formed. Using such drops, the sequence of connecting atoms in the molecule is depicted.

So, in the chlorine molecule, each atom has a completed external level of eight electrons (S 2 P 6), with two of them (electronic steam) to the same extent belong to both atoms.

Somewhat differently depict the connection in the oxygen molecule of 2. It is experimentally established that oxygen is a paramagnetic substance (drawn into a magnetic field). In his molecule there are two unpaired electrons. The structure of this molecule can be depicted as follows:

Unambiguous decision on the image of the electronic structure of the oxygen molecule has not yet been found. However, it cannot be depicted like this:

In nitrogen molecule N 2, atoms have three general electronic pairs:

It is obvious that the nitrogen molecule is stronger than oxygen or chlorine molecule than the significant inertness of nitrogen in chemical reactions is due.

Chemical bond carried out by electronic pairs is called covalent.

This is a two-electron and two-centered (holds two cores) communication.

Compounds with covalent bond are called homeopolar, or atomic.

There are two types of covalent communications: non-polar and polar.

In the case of a non-polar covalent bond, an electronic cloud formed by a common pair of electrons, or an electronic cloud of communication, is distributed in space symmetrically relative to the nuclei of both atoms.

An example is diatomic molecules consisting of atoms of one element: H 2 Cl 2, O 2, N 2, F 2, and more. In which the electron steam is equally belonging to both atoms.

In the case of polar covalent bond, the electronic cloud of communication is shifted to the atom with greater relative electronegitability.

An example is the molecules of volatile inorganic compounds: NS1, H 2 O, H 2 S, NH 3, etc.

The formation of the NS1 molecule can be submitted by the scheme:

The electron pair is shifted to the chlorine atom, since the relative electronegability of the chlorine atom (2.83) is greater than the hydrogen atom (2,1).

A covalent bond is formed not only due to overlapping single-electronic clouds, is the exchange mechanism for the formation of a covalent bond.

Another mechanism for the formation of a covalent bond is also possible - donor-acceptor. In this case, the chemical bond occurs due to the two-electron cloud of one atom and the free orbital of the other atom. Consider as an example the mechanism of formation of an ammonium ion NH +4. In the ammonia molecule, the nitrogen atom has a watered pair of electrons (two-electron
cloud):

The hydrogen ion is free (not filled) 1S-orbital, which can be designated as follows: H +. When forming an ammonium ion, a two-electronic cloud of nitrogen becomes common to atoms of nitrogen and hydrogen, i.e. It turns into a molecular electronic cloud. So, the fourth covalent bond arises.

The formation process of ammonium ion can be submitted by the scheme:

The hydrogen ion charge becomes common (it is delocalized, i.e. dispersed between all atoms), and a two-electron cloud (a vapor electron pair) belonging to nitrogen becomes common with hydrogen. In the diagrams, the cell image is often descended.

An atom providing a watered electronic pair is called a donor, and an atom accepting it (i.e. providing a free orbital) is called an acceptor.

The mechanism for the formation of a covalent bond due to the two-electron cloud of one atom (donor) and the free orbit of the other atom (acceptor) is called donor-acceptor. A covalent connection formed by this way is called donor-acceptor, or coordination, bond.

However, this is not a special type of communication, but only a different mechanism (method) of covalent communication. By properties, the fourth N-h-bond in the ammonium ion is no different from other connections.

Metal communication

Atoms of most metals at the external energy level contain a small number of electrons. So, one electron contains 16 elements, two - 58, three - 4 elements and not only - only in PD. The atoms of elements GE, SN and PB have at the outer level of 4 electrons, Sb and Bi - at 5, PO - 6, but these elements are not characteristic metals.

Metal elements form simple substances - metals. Under normal conditions, these are crystalline substances (except mercury). In fig. 3 shows the scheme of the crystal sodium lattice.

As can be seen, each sodium atom is surrounded by eight adjacent. On the example of sodium, we consider the nature of the chemical bond in metals.

At the sodium atom, as in other metals, there is an excess of valence orbitals and a lack of electrons.

Thus, the valence electron (3S 1) can occupy one of the nine-free orbitals - 3s (one), SP (three) and 3D (five).

Under rapprochement atoms as a result of the form crystal lattice Valented orbitals of neighboring atoms overlap,

due to which the electrons are freely moving from one orbital to another, communicating between all atoms of the metal crystal. This type of chemical bond is called a metal tie.

The metal bond form elements whose atoms at the outer level have little valence electrons compared to the total number of external energy orbitals, and valence electrons due to a small ionization energy are weakly held in atom.

Chemical bond in metal crystals is strongly delocalized, i.e. Electrons communicating, are commonplace ("Electronic Gas") and move throughout the piece of metal, as a whole electoral.

Metal bond is characteristic of metals in solid and liquid state. This is the property of the aggregates of atoms located in close proximity to each other. However, in a vapor state, atoms of metals, as well as all substances, are related to a covalent bond. Metal pairs consist of separate molecules (single andomic and ductomy). The bond strength in a crystal is greater than in a metal molecule, and therefore the process of the formation of a metal crystal proceeds with energy release.

Metal communication has some similarity with covalent, since it is based on the publicity of valence electrons. However, electrons that carry a covalent bond are near the connected atoms and are firmly connected with them. Electrons exercising metal communications, freely move throughout the crystal and belong to all its atoms. That is why crystals with a covalent bonding of fragile, and with metal - plastic, i.e. They change the form when they hit, rolled into thin sheets and stretched into wire.

Metal communications are explained physical properties Metals.

Hydrogen communications

Hydrogen bond is a kind of chemical bond. It can be intermolecular and intramolecular.

Intermolecular hydrogen bond arises between molecules, which includes hydrogen and highly electronegative element - fluorine, oxygen, nitrogen, less often chlorine, sulfur. Since in such a molecule, the overall electronic pair is strongly shifted from hydrogen to an atom of an electronegative element, and a positive charge of hydrogen is concentrated in a small volume, the proton interacts with a mean-free electronic pair of another atom or ion, to generalize it. As a result, a second, weak bond, called hydrogen-free.

Previously, hydrogen bonds reduced the electrostatic attraction between the proton and the other polar group. But it should be more correct that donor-acceptor interaction contributes to its education. For this connection, direction is characterized in space and saturation.

Usually, hydrogen communication is indicated by points and this indicate that it is much weaker than a covalent bond (approximately 15-20 times). Nevertheless, it is responsible for the Association of Molecules. For example, the formation of dimers (in liquid state they are most stable) water and acetic acid can be submitted by schemes:

As can be seen from these examples, two water molecules are combined by hydrogen bonds, and in the case of acetic acid, two acid molecules to form a cyclic structure.

The presence of hydrogen bonds is explained by a higher water boiling point (100 ° C) compared with hydrogen compounds of the elements of the oxygen subgroup (H 2 O, H 2 S, H 2 TE). In the case of water, it is necessary to spend additional energy for the destruction of hydrogen bonds.

Covalent bond is carried out at the expense of electrons belonging to both atoms involved in the interaction. Electricity of non-metals are large enough, therefore the transmission of electrons does not occur.

Electrons that are on overlapping electronic orbitals come to general use. At the same time, a situation is created in which the external electronic levels of atoms are filled, that is, an 8 or 2-electronic outer sheath is formed.

In contact with

A condition in which the electronic shell is fully filled, characterized by the lowest energy, and, accordingly, the maximum stability.

Education mechanisms two:

1. donor-acceptor;
2. exchange.

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

In the second - in a common pair, it comes one electron from each interaction participant.

Depending on what type of type - Atomic or molecular, compounds with a similar type of communication can differ significantly in physico-chemical characteristics.

Molecular substances Most often, gases, liquid or solids with low melting and boiling and boiling points, non-electric 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), nitrogen oxide V (N 2 O 5), water (H 2 O), chloride (HCl), fluoride hydrogen (HF), ammonia (NH 3), methane (CH 4), ethyl alcohol (C 2 H 5 OH), organic polymers and others.

Atomic substances exist in the form of durable crystals having high temperatures boiling and melting, not soluble in water and other solvents, many do not conduct electricity. As an example, a diamond can be brought, which has exceptional strength. This is explained by the fact that the diamond is a crystal consisting of carbon atoms connected by covalent bonds. There are no individual molecules in diamond. Also, such substances such as graphite, silicon (Si), silicon dioxide (SiO 2), silicon carbide (SiC) and others have atomic structure.

Covalent bonds can be not only single (as in the chlorine molecule CL2), but also double, as in O2 oxygen molecule, or triple, as, for example, in nitrogen molecule N2. In this case, the triples have greater energy and are more durable than double and single.

Covalent bond can be formed both between two atoms of one element (non-polar) and between atoms of various chemical elements (polar).

Indicate the formula of the compound with a covalent polar bond is not difficult if you compare the values \u200b\u200bof electrical negotiations that are part of the molecules of atoms. No difference in electronegativity will determine non-polarity. If there is a difference, then the molecule will be polar.

Do not miss: Education mechanism, specific examples.

Covalent non-polar chemical

Characteristic for simple substances Nemmetalov. Electrons belong to atoms equally, and the electron displacement does not occur.

An example is the following molecules:

H2, O2, O3, N2, F2, CL2.

Exceptions are inert gases. Their external energy level is fully filled, and the formation of molecules them is energetically not profitable, and therefore they exist in the form of individual atoms.

Also, an example of substances with a non-polar covalent bond will be, for example, pH3. Despite the fact that the substance consists of various elements, the values \u200b\u200bof electro-negativeness of the elements are actually not different, which means that the electronic pair displacements will not happen.

Covalent Polar Chemical Communication

Considering a covalent polar bond, examples can be brought by many: HCl, H2O, H2S, NH3, CH4, CO2, SO3, CCL4, SiO2, SO3, CCL4, SiO2, CO.

it is formed between the atoms of non-metals with different electronegitability. In this case, the kernel of the element with greater electronegitability attracts general electrons closer to itself.

Covalent polar communication formation scheme

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

In the picture, the interaction in the hydrochloric acid molecule is clearly represented.

A pair of electrons belongs to both atoms, and the second, in both, thus, the external levels are filled. But more electronegative chlorine attracts a couple of electrons a little closer to himself (while it remains common). The difference in electronegativity is not enough so that the pair of electrons moves to one of the atoms completely. As a result, a partial negative charge has a chlorine and a partial positive hydrogen. HCL Molecule is a polar molecule.

Phone physico-chemical properties

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

Covalent bond, depending on how the general electron pair occurs, can be formed by exchangeor donor-acceptor mechanism.

Exchangeable mechanismthe formation of covalent bond is being implemented in cases where a nuclear orbital and an unpaired electron located on this orbitaly are also involved in the formation of a general electron pair from each atom.

For example, in a hydrogen molecule. The interacting hydrogen atoms containing single electrons with opposite spins in atomic S-orbitals form a common electron pair, the movement of which in the molecule H 2 is carried out within the boundaries of the σ-molecular orbital arising from the fusion of two S-atomic orbitals:

In the ammonia molecule, the nitrogen atom, having three single electrons and one electron pair on four atomic orbitals, forms three general electronic pairs with s-electrons of three hydrogen atoms. These electronic pairs in the NH 3 molecule are located on three σ-molecular orbital, each of which occurs when the nuclear nitrogen atomic orbital is fused with the hydrogen atom orbital atom:

Thus, in the ammonia molecule, the nitrogen atom forms three σ- bonds with hydrogen atoms and has virtual electronic pair.

Donor-acceptor mechanism The formation of covalent bond is implemented in cases where one neutral atom or ion (donor) It has an electronic pair on the atomic orbital of the external energy level, and another ion or a neutral atom (acceptor) - Free (vacant) orbital. When merging atomic orbitals, a molecular orbital arises, on which there is a general electron pair, which previously belonging to the donor atom:

According to the donor-acceptor mechanism, for example, the formation of a covalent bond between the ammonia molecule and the hydrogen ion with the occurrence of ammonium ion + is occurring. In the ammonia molecule, the nitrogen atom in the outer layer has a free electron steam, which allows this molecule to act as a donor. The hydrogen ion (acceptor) has a free S-orbital. Due to the fusion of atomic orbitals of the nitrogen atom and hydrogen ion, a σ-molecular orbital arises, and the free pair of electrons of the nitrogen atom becomes common to connecting atoms:

Or H + + NH 3 [H NH 3] +

In an ammonium ion + a covalent bond N-H, formed by a donor-acceptor mechanism, equivalent in energy and three to three other covalent n-H connectionsFormed by the exchange mechanism.

The borom atom forms a boron fluoride molecule BF 3 due to overlapping electronic orbitals occupied in an excited state of unpaid electrons with electronic fluorine orbitals. At the same time, at the boron atom, one vacant orbital retains, at the expense of which the fourth chemical bond can be formed by the donor-acceptor mechanism.

Communication formed by donor-acceptor mechanism is often called donor-acceptor coordination or coordinated. However, this is not a special type of communication, but only a different mechanism for the formation of a covalent bond.

The donor-acceptor mechanism for the formation of a covalent bond is characteristic of complex compounds: the response of the acceptor is usually performed by D-metals, which can usually provide two, four or six free atomic orbitals S-, P-, D-type, which significantly expands their capabilities to form covalent Communication.

For example, AG + and CU 2+ ions, respectively, provide two and four free atomic orbitals, and the donor of electronic pairs can be, for example, two or four ammonia or cyanide ion molecules:

Acceptor donor

In these cases between donors and acceptor, covalent bonds arise with the formation of complex cations (silver and copper ammonia) or anion (copper cyanide).