Named after Johannes Diderik van der Waals (1837-1923), the simplest definition is that they are weak attractive forces that contribute to bonding between molecules or atoms. They are called weak forces because they are weaker than the chemical bonds between molecules or atoms. The starting point for understanding these forces is the four forces of nature: gravity, electromagnetism, the weak nuclear force, and the colour force. van der Waals forces are in a sense a form of electromagnetism. Thinking in terms of electrons in atoms, what happens is that when the electrons of one atom get close to those of another, they push each other away as like charges repel. To use a metaphor, the positive charges on the very much larger protons can ‘see’ each other, and in doing so push each other away so that the objects never touch one another. Without this repellant process, objects would fall through the Earth to its center and if sitting on a chair we would fall to the ground. Under certain circumstances, van der Waals forces can be attractive, and under this regime they produce the lattice structure of atoms in a crystal. Because they attract the atoms and molecules to one another while holding them relatively still, they in fact impart the ‘solidity’ we perceive in solid objects. The balance between attractions and repulsions plays an important role in many molecular complexes such as the DNA double helix (and thus nucleic acids), the structure and function of proteins, cell adhesion phenomena including cell recognition, and membrane formation and transport. One of the major problems in understanding the role of van Waals forces in such contexts is to distinguish their effects from hydrophobic interactions (i.e., solvant-solute interactions involving the tendency of non-polar or insoluble-in-water molecules to come together as they are excluded by a polar solvent like water).
See Cell adhesion molecules (CAMS), Cell recognition molecules, DNA double helix, Force, Protein, Proton