Two types of covalent bonds are formed depending upon the electro negativity of the combining elements.
1. Non-polar covalent bond
2. Polar covalent bond
Non-polar covalent bond
During the Formation of a covalent bond between two atoms which belong to the same element, the pair which is shared will lie in the middle of the two atoms. This means the atoms involved in sharing will share the electrons equally. Hence molecule obtained will be electrically symmetrical. Electrically symmetrical means centre of the positive charge coincides with the centre of the negative charge. This type of covalent bond formed is known as a non-polar covalent bond.
For example: The bonds in the molecules H2, O2, Cl2 etc., are non-polar covalent bonds.
H• + x H ———> H x H
: Ö: +: Ö: ———–> : Ö: Ö:
Polar covalent bond
Formation of a covalent bond between two atoms which belong to different element is known as a polar covalent bond. The electron affinity of the atoms involved in polar covalent bond is different. The bonding pair of electrons will lie more towards the atoms which have higher electron affinity, for electrons during the formation of polar covalent bond. As the said electron pair do not lie exactly midway between the two atoms. The atom having higher affinity for electrons gets a slightly negative charge and the atom with lesser affinity for electrons develops a slightly positive charge. Such molecules are called ‘polar molecules’.
For example: Hydrogen chloride (HCl) molecule forms polar covalent bond. The bonding of hydrogen and chlorine atoms lies more towards Cl atom (because Cl is more electronegative) in the shared pair of electrons. Therefore, Cl atom acquires a slight negative charge, and H atom a slight positive charge.