EoS: Permanent Dipoles

Permanent Dipoles

Some molecules, while not having a net charge, have an asymmetrical distribution of charges (Ex: water, ammonia, acetone).


The dipole moment, $\mu$, of a molecule is the charge times the distance separating the charge(s) and has units of Debye (D) (which is 3.336x$10^{-30}Cm$).

$\mu = Ql$

$F_{12} \propto -\frac{\mu_1^2\mu_2^2}{r^7}$

$\Gamma_{12} \propto -\frac{\mu_1^2\mu_2^2}{r^6}$


The potential energy of a dipole drops off dramatically faster with $r$ than the energy between point charges. (Also, because it is an even power, there is a negative in both expressions.)