force of attraction of a dipolar molecule for another molecule or
ion depends on how much charge is separated and how great the separation
is. The strength of a dipole is measured by its dipole moment, u.
If two equal and opposite charges, +q and -q, are separated by a distance
r, then the dipole moment is defined as
u = qr
Either doubling the charges, or doubling the separation between them,
has the effect of doubling the strength with which the molecule will
attract its neighboring molecules. The dipole moment of a molecule
is an easy quantity to measure and is a useful indication of a molecule's
chemical and physical behavior.