CoachA van der Waals interaction is a weak attraction between neighbouring molecules, which exists between all molecules, polar or not: the electrons of each molecule are constantly moving, and the momentary uneven charges of one molecule attract those of its neighbours. Between polar molecules, the permanent partial charges add a further attraction.
Examples
Example 30.16 (Three solids)
Sodium chloride, an ionic solid, melts at ; ice, held by hydrogen bonds, at ; solid methane, held only by van der Waals interactions between small molecules, far below .