the first time such a concept as a covalent bond chemists spoke after the opening of Gilbert Newton Lewis, who described the bond as a socialization of the two electrons.More recent studies have described, and the principle of a covalent bond.Word covalent can be seen in the framework of chemistry as the ability of atoms to form bonds with other atoms.
Here is an example:
There are two atoms with minor differences in electronegativity (C and CL, C and H).As a rule, the atoms, the structure of the electron shell which is as close as possible to the structure of the electron shell of the noble gases.
When these conditions there is the attraction of the nuclei of these atoms to the electron pair which is common to them.Then the electron clouds are not simply superimposed on each other, as in ionic bonding.The covalent bond provides a secure connection between two atoms due to the fact that the electron density is redistributed and modified energy of the system, which is caused by "retraction" in the internuclear space of a single atom electron cloud of another.The more extensive mutual overlapping of the electron clouds, the connection is considered to be more durable.
Hence, covalent bond - is education, which arose through the mutual socialization of two electrons belonging to two atoms.
Generally, substances with a molecular lattice is formed by a covalent bond.Characteristic molecular structure are melting and boiling at low temperatures, poor water solubility and low electrical conductivity.From this we can conclude that at the heart of building elements such as germanium, silicon, chlorine, hydrogen - covalent bond.
Properties are typical for this type of connection:
- saturation. Under this property is usually understood the maximum number of connections that they can establish specific atoms.Determined by the number of the total number of orbitals in atoms that may be involved in the formation of chemical bonds.The valence of the atom, on the other hand, may be determined by the number of already used for this purpose orbitals.
- Orientation .All the atoms tend to form the strongest possible bond.Maximum strength is achieved in the case of coincidence of the spatial orientation of the electron clouds of two atoms, as they overlap each other.Furthermore, it is a property of a covalent bond as a thrust effect on the spatial arrangement of the molecules of the organic substance that is responsible for their "geometrical shape".
- polarizability. The basis of this position is the notion that there is a covalent bond of two types:
- polar or non-symmetrical.Communication of this kind may form only atoms of different types, i.e.those whose electronegativity varies greatly, or in cases where the total electron pair asymmetrically divided.
- nonpolar covalent bond occurs between atoms, the electronegativity of which is almost equal, and the electron density distribution uniform.
In addition, there are certain quantitative characteristics of the covalent bond:
- binding energy .This parameter characterizes the polarity of the bond in terms of its strength.Under energy is meant the amount of heat that was required to break bonds between two atoms, as well as the amount of heat that has been allocated at their junction.
- Under bond length and molecular chemistry refers to the length of the line between the nuclei of two atoms.This option is also characterizes the strength of the bond.
- dipole moment - value which characterizes the polarity of the valence bond.