Why are London dispersion forces attractive?

[fedaykin]

I've looked around in my basic chemistry books and haven't seen this directly answered, and I'm having trouble with it on the internet too.

Wouldn't said force be repulsive just as often as attractive and therefore have no net force?

[Ed Aboud]

London forces are considered both attractive and repulsive fedaykin!
Hope that helps.

[Ygggdrasil]

No Ed, London dispersion forces are always attractive. These are also known as induced dipole-induced dipole interactions. In one molecule, a transient dipole can be formed from there temporarily being more electrons on one side of the atom/molecule than the other. This transient dipole will then induce a dipole (uneven distribution of electrons) in a nearby atom/molecule. This induced dipole in the second molecule will always point in the same way as the dipole of the first molecule, resulting in an attractive interaction. A dipole will never induce a dipole that results in a repulsive interaction (as an analogy, putting a bar magnet next to another bar magnet will never cause the second magnet to align itself to repel itself from the first magnet).

[fedaykin]

Ah, thank you very much. I'm trying to become more diligent in my reading. That's hard for me, especially at 3:00 a.m.