What do dispersion forces depend on

Figure 1: Dispersion Interaction with an instantaneous dipole on one He atom inducing a dipole on a nearby He atom. If it were not for dispersion forces, the noble gases would not liquefy at any temperature since no other intermolecular force exists between the noble gas atoms. The low temperature at which the noble gases liquefy is to some extent indicative of the magnitude of dispersion forces between the atoms.

Electron distribution around an atom or molecule can be distorted. This distortion is called the polarizability. Figure 2: Dispersion interaction in the gas phase. It is possible that these forces arise from the fluctuating dipole of one molecule inducing an opposing dipole in the other molecule, giving an electrical attraction. It is also possible that these interactions are due to some sharing of electrons between the molecules in "intermolecular orbitals", similar to the "molecular orbitals " in which electrons from two atoms are shared to form a chemical bond.

The stronger farther-reaching electrical forces from ions and dipoles are considered to operate in addition to these forces. The polarizability is used to describe the tendency of molecules to form charge separation. Induced dipole occurs when a molecule with an instantaneous dipole induces a charge separation on other molecule. The result is a dipole-dipole attraction. In F 2 , both F atoms are holding all the electrons really tightly, trying to grab them and not share.

In contrast, iodine is really soft. It's electrons are far away from the nucleus, and they can move around easily. If they all happen to move one direction, creating a temporary dipole, the other molecules nearby can adjust, making more dipoles to attract the first one.

These are called induced dipoles, because they appear in response to the original accidental dipole. Lots of induced dipoles can create attraction between molecules, called London dispersion forces. London dispersion forces are always present, but they vary widely in strength. In light atoms, they are very small, because there aren't many electrons and they are held tightly.

In large atoms, they can be very big, because the atoms are very soft and easy to polarize. Generally, London dispersion forces depend on the atomic or molecular weight of the material.

What is the dipole moment of nitrogen trichloride? How does dipole moment affect molecules in solution? What causes dipole moment? See all questions in Dipoles. Impact of this question views around the world. You can reuse this answer Creative Commons License.