Van der Waals forces

In physical chemistry, the van der Waals forces, named after Dutch scientist Johannes Diderik van der Waals, are distance dependent interactions between atoms. Unlike hydrogen or covalent bonds, these attractions are not a result of any chemical electronic bond and so this force is more susceptible to being perturbed. Being the weakest of the weak chemical forces, with a strength between 0.4 and 4kJ/mol they may still support an integral structural load when multitudes of such interactions are present. Such a force results from a transient shift in electron density. Specifically, as the electrons are in orbit of the protons and neutrons within an atom the electron density may tend to shift more greatly on a side. Thus, this generates a transient charge to which a nearby atom can be either attracted or repelled by. When the interatomic distance of two atoms is greater than 0.6nm the force is not strong enough to be observed. In the same vein, when the interatomic distance is below 0.4nm the force becomes repulsive. If no other forces are present, the point at which the force becomes repulsive rather than attractive as two atoms near one another is called the Van der Waals contact distance. This results from the electron clouds of two atoms unfavorably coming into contact. It can be shown that van der Waals forces are of the same origin as the Casimir effect, arising from quantum interactions with the zero-point field. The resulting van der Waals forces can be attractive or repulsive.

The term includes:

It is also sometimes used loosely as a synonym for the totality of intermolecular forces. Van der Waals forces are relatively weak compared to covalent bonds, but play a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics. Van der Waals forces define many properties of organic compounds and molecular solids, including their solubility in polar and non-polar media.

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