Covalent Bond:

A Covalent Bond is a bond formed by the sharing of one, two or three pairs of electrons by two atoms. The bonded atoms will experience some level of increased stability as a result of the sharing process. The shared electrons will reside primarily between the two bonded nuclei. This will produce an electrostatic force of attraction between the nuclei and the shared electron cloud. This force holds the bonded system together.

The more electrons occupying the area between the nuclei, the greater the attraction and the stronger the bond. Consequently, all other factors being equal, a triple bond is stronger than a double bond which is stronger than a single bond. It is not possible to ever have more than three pairs of electrons between the two bonded nuclei. Any number beyond three pairs would increase the area of negative charge so much that the extra electron pairs will always be pushed out of the region and the bond would be destroyed.

In the covalent bond process, the electrons are not always shared equally. If there is a substantial difference between the electronegativities of the two bonded atoms, then the electrons will reside closer to the atom with the higher electronegativity. This will lead to a covalent bond that is polar. When the atoms have similar electronegativity values, then the electrons are shared more equally and the bond is referred to as being nonpolar.