Types of Covalent Bonding

The nature of a covalent bond depends on the relative electronegativities of the atoms sharing the
electron pairs. Covalent bonds are polar or nonpolar depending on the difference in
electronegativities between the atoms.

POLAR COVALENT BONDS

Polar covalent bonding occurs between atoms with small differences in electronegativity. The
bonding electron pair is not shared equally, but pulled more toward the element with the higher
electronegativity. Yet the difference in electronegativity is not high enough for complete electron
transfer (ionic bonding) to take place. As a result, the more electronegative atom acquires a partial
negative charge, δ–, and the less electronegative atom acquires a partial positive charge, δ+, giving
the molecule partially ionic character. For instance, the covalent bond in HCl is polar because the
two atoms have a small difference in electronegativity. Chlorine, the more electronegative atom,
attains a partial negative charge and hydrogen attains a partial positive charge. This difference in
charge is indicated by an arrow crossed (a plus sign) at the positive end pointing to the negative end:

This small separation of charge generates what is known as a dipole moment.

NONPOLAR COVALENT BONDS

Nonpolar covalent bonding occurs between atoms that have the same electronegativities. The
bonding electrons are shared equally, with no separation of charge across the bond. Not
surprisingly, nonpolar covalent bonds occur in diatomic molecules with the same atoms. Certain
elements exist under normal conditions only as diatomic molecules: N 2 , O 2 , F 2 , Cl 2 , Br 2 , I 2 , H 2 . Their
positions in the periodic table form an inverted L-shape towards the top right, excluding the noble
gases.