The electronegativity of an atom is the tendency of an atom in a compound or molecule to attract bonding electrons unto itself. A polar bond is formed when there is an uneven distribution of charges in the molecule brought about by differences in the electronegativities of the atoms in the bonds. These differences create regions of partially positive and partially negative charges. A nonpolar bond only have very small differences in the electronegativity of the bonding atoms.
Generally, when the difference in electronegativity is less than 0.5, the bond is polar. When the difference is between 0.5 and 1.7, the bond is polar. Finally, when the difference is greater than 1.7, the bond is ionic, which means that the bonding electron is very much attracted to the highly electronegative atom that it is transferred to the said atom instead of merely being shared by the atoms in the bond.
