Van der Waals forces
Entry by Robin Kirkpatrick AP 225, 2011
Van der Waals forces refer to the sum of the forces between molecules, exlcuding those that are ionic or covalent in nature.
These forces are a result of:
1. Repulsion, as a result of the Pauli Exlcusion principal. 2. Keesom/electrostatic interactions between charges, dipoles, quadrapoles, and (in general) multipoles. 3. Induction/Debye forces, which result from interaction of a permanent multipole with an induced multipole. 4. Dispersion/London Forces, which result from the interaction of instantaneous multipoles.
While induction and dispersion forces are attractive, electrostatic forces can be either attractive or repulsive depending on oreintation. As a result, random thermal motion is usually enough to disrupt the electrostatic component. The Lennard-Hones potential is an approximation to the isotropic component of the Van der Waals force, and is given below by: