Van der Waals forces are the weakest intermolecular force and consist of dipole-dipole forces and dispersion forces.
Dipole-dipole forces are the attractive forces that occur between polar molecules.
A molecule of hydrogen chloride has a partially positive hydrogen atom and a partially negative chlorine atom. In a collection of many hydrogen chloride molecules, they will align themselves so that the oppositely charged regions of neighboring molecules are near each other.
London Dispersion Forces
London dispersion forces are the intermolecular forces that occur between atoms and between nonpolar molecules as a result of the motion of electrons.
Van der Waals forces are weak interactions between molecules that involve dipoles.
Polar molecules have permanent dipole-dipole interactions.
Non-polar molecules can interact by way of London dispersion forces.