About the van der Waals force

Van der Waals Forces is the electrostatic attraction between dipoles formed by uncharged molecules. To simplify what the above sentence mean, it is the kind of attraction between uncharged molecules.

Van der Waals force include three types of intermolecular attractions. 1) Dipole-dipole Interactions 2) Dipole induced dipole interactions 3) Instantaneous dipole induced dipole Interactions

1) Dipole-dipole interactions is the interaction between two permanent dipoles. Permanent dipole means the uncharged molecule is composed of two atoms, which have difference in electronegativity. The more electronegative atom tends to attract the bonded electron, result in slightly -ve charged, and the less electronegative atom becomes electron difficient, result in slightly +ve charged. The -ve end of the molecule will be attracted by the +ve end of another molecule, this attraction is called Permanent dipole dipole interaction. (e.g. HCl)

2) Dipole induced dipole interactions is the interaction between one permanent dipole and one non-polar molecule. When the non-polar molecule comes close to the permanent dipole, The non-polar molecule will be induced to form a temporary dipole. The induced dipole will be oriented in opposite with the permanent dipole, result in the attraction between the induced dipole and permanent dipole. (e.g. HCl and He)

3) Instantaneous dipole induced dipole interactions is the interaction between two non-polar molecules. The non-polar molecules normally have electron cloud uniformly distributed around the nuclei, however, because of the fluctuation of electrons at any particular instant, +ve and -ve charge will exist temporarily, therefore temporary dipole will be produce at any particular instant. The instantaneous induced dipoles will be oriented in oppositie position, result in the attraction between the instantaneous induced dipoles. This attraction is also called London Dispersion Force, London Force, or Dispersion Force. (e.g. Halogen, noble gas)