When two electrons are shared by two atoms covalent type compound is formed. Electron from outermost shell of one atom (which is also called valence shell electron) can be shared by another atom to complete its outermost shell which makes both atoms more stable. The electron pair shared by both the atoms is known as shared pair or bonding pair of electron. If there is no electronegativity difference between two atoms, then non-polar covalent bond is formed between both the atoms. If one atom is more elctronegative than other one, then the covalent polar bond is formed.