What are the four different intermolecular forces?

The four intermolecular forces (forces between molecules) are hydrogen bonding, permanent dipole–permanent dipole, permanent dipole–induced dipole and instantaneous dipole–induced dipole. These vary in strength, and I have listed these from the strongest (hydrogen bonding) to the weakest (instantaneous dipole–induced dipole). Hydrogen bonding can only take place between molecules containing nitrogen, oxygen or fluorine. The reason for this is that they are all very electronegative and have at least one lone pair of electrons. They form a hydrogen bond with a hydrogen atom on the other molecule. I remember these atoms as 'NOF', and they are all adjacent to each other on the Periodic Table. The latter three forces are collectively called Van der Waals forces, and the particular Van der Waals force present depends on the polarity of the molecules involved. Permanent dipole–permanent dipole forces exist between polar molecules; permanent dipole–induced dipole forces exist between a polar molecule and a non-polar molecule; and instantaneous dipole–induced dipole forces exist between non-polar molecules. The latter two here, also known as London forces, are short-range, and increase in strength as the relative molecular mass of the molecule increases. It is important to determine the polarity of the molecules involved to work out which type of intermolecular force is present.