In pure covalent bonds, the electrons are shared equally. In polar covalent bonds, the electrons are shared unequally, as one atom exerts a stronger force of attraction on the electrons than the other.

Covalent bonds form when electrons are shared between atoms and are attracted by the nuclei of both atoms. The ability of an atom to attract a pair of electrons in a chemical bond is called its electronegativity.

covalent bond — bond formed when electrons are shared between atoms. polar covalent bond — covalent bond between atoms of different electronegativities; a covalent bond with a positive end and a negative end. pure covalent bond — (also, nonpolar covalent bond) covalent bond between atoms of identical electronegativities. electronegativity — tendency of an atom to attract electrons in a bond to itself.