London Dispersion vs. Dipole-Dipole

[Labiba Sardar 2A]

When do you know that a molecule with London dispersion forces will have stronger intermolecular forces than a molecule with dipole-dipole interactions? More specifically, why aren't the dipole-dipole interactions stronger than the London dispersion forces?

An example can be H2S (LDF's) vs. H2Se (dipole-dipole). H2S is stronger.

[Chem_Mod]

London dispersion forces increase in strength the larger (and thus more electron dense) the molecule is. You do not have to know the threshold in size for this to occur, but in general, dipole-dipole forces will be stronger. Additionally, H2S can also participate in dipole-dipole interactions, and stronger ones than H2Se since S is more electronegative than Se, so I am not sure where you got that example from.

[Mai V 4L]

Does anyone have a video they think is a good reference for this topic? Will this be on the final?