Intermolecular forces are ones which act between molecules. There are 3 types of intermolecular forces:
Instantaneous and Induced Dipoles
The electrons in a molecule are constantly moving around at random. At a single moment in time, there is likely to be a higher concentration of electrons at one end of a molecule than at another. This makes the specific molecule polar for that moment in time. The negative end of that molecule will repel electrons in an adjacent molecule, and the result is a very small negative charge on one end of a molecule next to a very small positive charge on another molecule - this is induced dipole interaction, which occurs in everything.
The forces involved are very weak. With more electrons, the forces get...