Polar Character of covalent Bond
Two types of covalent bonds are formed depending upon the electronegativity of the combining elements.
Non-polar covalent bond
When a covalent bond is formed between two atoms of the same element, the shared electron pair will lie exactly midway between the two atoms i.e. the electrons are equally shared by the atoms.
The resulting molecule will be electrically symmetrical i.e., centre of the negative charge coincides with the centre of the positive charge.
This type of covalent bond is described as a non-polar covalent bond. The bonds in the molecules H2, O2, Cl2 etc., are non-polar covalent bonds.
Polar covalent bond
The bond between two unlike atoms, which differ in their affinities for electrons is said to be a polar covalent bond.
When a covalent bond is formed between two atoms of different elements, the bonding pair of electrons will lie more towards the atom, which has more affinity for electrons.
As the said electron pair do not lie exactly midway between the two atoms, the atom with higher affinity for electrons develops a slight negative charge and the atom with lesser affinity for electrons, a slight positive charge. Such molecules are called 'polar molecules'.
In the hydrogen chloride (HCl) molecule, 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. This causes the covalent bond between H and Cl to have an appreciable ionic character.
The compounds having polar bonds are termed polar compounds.
Polar substances in their pure forms, do not conduct electricity, but give conducting solutions when dissolved in polar solvents.