Instantaneous dipole attraction

Instantaneous dipole attraction involves molecules without a permanent dipole. Molecules can be thought to be surrounded by a negatively charged cloud of constantly moving electrons. If at any particular instant more of the electrons happen to be more at one side of the molecule than another, this side becomes more negative, whereas the other side becomes more positive - a dipole is developed.

Although this dipole is only evident for a very short time, it can cause intermolecular attractions to occur through induced-dipole attraction.