i. Covalent bonds are formed between two atoms of the same or different elements.
ii. When a covalent bond is formed between atoms of same element such as H-H, F-F, ClCl, etc., the shared pair of electrons is attracted equally to both atoms and is situated midway between two atoms. Such covalent bond is termed as nonpolar covalent bond.
iii. When a covalent bond is formed between two atoms of different elements that have different electronegativities, the shared electron pair does not remain at the centre.
The electron pair is pulled towards the more electronegative atom resulting in the separation of charges.
This give rise to dipole.
The more electronegative atom acquires a partial -ve charge and the other atom gets a partial +ve charge.
Such a bond is called as polar covalent bond.
The examples of polar molecules include HF, HCl, etc.
Fluorine is more electronegative than hydrogen, therefore, the shared electron pair is more attracted towards fluorine and the atoms acquire partial +ve and -ve charges, respectively.
iv. Polarity of the covalent bond increases as the difference in the electronegativity between the bonded atoms increases.
When the difference in electronegativities of combining atom is about 1.7, ionic percentage in the covalent bond is 50%.
