The covalent bond. Chemistry summary on the covalent bond: definition, polar bond and homopolar bond.
Covalent Bond: summary and definition:
Here is a summary of chemistry on polar and homopolar covalent bond . – The tendency of two or more atoms , equal or different, to spontaneously bond together forming chemical bonds, is an aspect of the tendency of every system existing in nature to decrease its energy content.
Therefore, if two atoms placed in contact react spontaneously with each other, it can in any case be written
A + B → AB + energy, and this energy is released to the outside.
The covalent bond between two atoms consists of the sharing of a pair of electrons. It can be represented with a simple dash or, in the Lewis representation , with a pair of dots representing the electrons.
Homopolar Covalent Bond:
The homopolar bond is a covalent bond that occurs between two atoms of the same type.
For example: the formation of the hydrogen molecule H2 which can be represented as
H + H → H – H or H• + •H → H:H
If more than one pair of electrons is shared, multiple bonds can also occur : double bonds or triple bonds are formed if two or three pairs of electrons are shared, respectively.
Polar Covalent Bond:
The polar covalent bond is formed between two different atoms, two nonmetals, with an electronegativity difference between 0.4 and 1.9.
In a molecule of this type, the more electronegative element attracts electrons more and the bonding pair is no longer equidistant from the two nuclei, but shifted toward the more electronegative nucleus. An electric dipole is formed , because one part of the molecule is more positive and the other is more negative.
For example, since chlorine is much more electronegative than hydrogen, in the molecule of hydrochloric acid HCl, the two shared electrons are arranged much closer to the chlorine than to the hydrogen. The H and Cl atoms of the HCl molecule are linked not only by the shared electrons, but also by the electrostatic attraction between the positive and negative parts of the molecule.
