Dipole moment

Molecules are formed by sharing electrons. In a molecule, if there is a pair of electrons, one with negative charge and the other one with positive charge and if the center of the negative charge do not coincide with the center of the positive, then the extent of polarity in this covalent molecule is known as the dipole moment.

Dipole moment = magnitude of the charge x distance of separation

Dipole moment is a vector quantity and is represented by a small arrow with tail at the positive center and head pointing towards a negative center.
For example, the dipole moment of HCl molecule is 1.03 D and that of H₂O is 1.84 D. The dipole of HCl may be represented as follows: