A pair of separated opposite electric charges. The dipole moment is the product of the positive charge and distance between the charges. Dipole moments are often state in debyes; the SI unit is the coulomb metre.

In a diatomic molecule, such as HCI, the dipole moment is a measure of the polar nature of the bond i.e. the extent to which the average electron charge is displaced towards one atom.

In a polyatomic molecule, the dipole moment is the vector sum of the dipole moments of the individual bonds.

In a symmetrical molecule, such as tetrachloromethane (CCI4), there is no overall dipole moment, although the individual C-CI bonds are polar.