Question

Question #da032

Answer 1

These molecules are all nonpolar. So they can interact among themselves by means of the so called "London dispersion forces". This is the name which was given, after the German-american physicist Fritz London's theory, in 1930, to those forces that are caused by temporary dipoles, which are generated everytime two nonpolar molecules get very close due to random movements and thermal motion. The electron cloud becomes uneven respect to positive charge distribution of the nuclei. These temporary dipoles induce a short lived dipole in other neighbor molecules, and the "London Dispersion Forces" (LDF) are the attractive forces among the molecules that have become temporary polarized.
The LDF are weak and short ranged, i.e. rapidly decreasing with distance, as much as `1/r^6`. And this is really more rapid than `1/r^3` decrement or "fading" pattern for the attraction between a charge and a dipole or `1/r^2` rate between two opposite charges. LDF attractions are normally weaker than forces between permanently polar molecules, forces between molecules and ions, or hydrogen bonds, but their strength is higher for bigger molecules, i.e. molecules with more electrons and larger surface.

I think this video can be helpful: Bozeman's description of LDF