Applications of Dipole moment:
(a) In determining the polarity of bonds:
As μ = e x d, obviously greater is the magnitude of dipole moment, higher will be the polarity of the bond. This is applicable to molecules containing only one polar bond like HCL, HBr etc. In non-polar molecules like H2, O2,N2 the dipole moment is zero. It is because there is no charge separate in these molecules [e = 0].
Thus dipole moment can also be used to distinguish between polar and non-polar molecules.
(b) In the calculation of percentage ionic character: Take an example of HCI. Its μ = 1.03 D If HCl is 100% ionic. Each red would carry charge- one unit i.e. 4.8 x 10−10 e.s.u (bond length) in H - CI - 1.275 Å
\(\therefore\) For 100% kric character, dipole moment will be
μionic = e x d
= 4.8 x 10-10 e.s.u x 1.275 x 10-8 cm
= 6.12 x 10-18 e.s.u cm
= 6.12 D
\(\therefore\) % ionic character
= \(\frac{\mu_{observed}}{\mu_{ionic}}\) x 100 = \(\frac{1.03}{6.12}\) x 100 = 16.83
(c) In determining the symmetry (or shape) molecules: Dipole moment is an important property in determining the shape of molecules containing 3 or more atoms. For instant if any molecule possesses two or more polar bonds, it will not be symmetric if it possesses some net molecular dipole moment as in case of water (H2O) μ = 1.84 D and ammonia (μ =1.49 D). But if a molecule contains a number of similar atoms linked to a central atom, the overall dipole moment of the molecule is found out to be zero, this will imply that the molecule is the symmetrical as is the case of CO2, BF3, CH4, CCI4 etc.
