A covalent bond involves the sharing of a pair a of electrons between two atoms. When the atoms are alike ,as in the case of the H-H bond of H2 ,the bonding electrons are equally shared. That is, the electrons spend equal time in the vicinity of each atom. But when the two atoms are of different elements ,the bonding electrons need not be shared equally. A polar covalent bond is formed when the bonding electrons spend more time near one atom than the other.For example,in the case of the HCl molecule ,we know that the bonding electrons spend more time near the chlorine atom than the hydrogen atom. Figure 7.4 shows the distribution of electrons in the H—Cl bond. Thus the H-Cl bond is polar covalent.