Charge transfer in groups of atoms lead to separate centers of charge in molecules resulting in a dipole moment. In polar molecules a permanent charge transfer generates a permanent electric dipole moment. Unpolar molecules can be polarized by electric or magnetic fields resulting in charge transfer with separate cebters of charge which are called induced dipoles. Thus e.g. metal surfaces can polarize unpolar oil molecules by their electromagnetic fields so that the molecules can be adsorbed by the surface.