“The product of magnitude of negative or positive charge (q) and the distance (d) between the centres of positive and negative charges is called dipole moment”.
µ = Electric charge bond length
As q is in the order of 10–10 esu and d is in the order of 10–8 cm, m is in the order of 10–18 esu cm. Dipole moment is measured in “Debye” (D) unit. 1D = 10-18 esu cm 3.33×10-30 coulomb metre (In S.I. unit)
Dipole moment is indicated by an arrow having a symbol (→) pointing towards the negative end. Dipole moment has both magnitude and direction and therefore it is a vector quantity
(1) Dipole moment is an important factor in determining the geometry of molecules.
(2) Every ionic compound having some percentage of covalent character according to Fajan's rule. The percentage of ionic character in compound having some covalent character can be calculated by the following equation.
The % ionic character = (Observed µ/Theoreticalµ) × 100.
(3) The trans isomer usually possesses either zero dipole moment or very low value in comparison to cis–form