Question

How do I figure out the intermolecular attractive forces between molecules? I have this question as my homework: What kinds of intermolecular attractive forces (dipole-dipole, London, hydrogen bonding) are present in the following substances?
HF
PCl3
SF6
SO2
The answers are HF: dipole-dipole, london forces. PCl3: dipole-dipole, london forces
SF6: London forces
SO2: dipole-dipole, london
Why? and how can I figure out the geometry of them?

Answer 1

I'm gonna go over some theory, but if it gets to general or just not understandable let me know.
Hydrogen bonding are special in such a way that molecules that posses them are independent of their specific identity. It is a attractive interaction that arises from a link on the following form:
X-H * * * Y
Here are X and Y highly electronegative elements and Y processes a lone pair. In theory we usually say that hydrogen binding is limited to the atoms N, O and F.

Answer 2

London forces also known as "induced-dipole-induced-dipole interactions" and are in principle found in every molecule. The interaction occurs from the transient dipoles all molecules have as a result of fluctuations in the instantaneous positions of electrons.

Answer 3

Dipole-dipole arises when we are able to set up a polarity in the molecule. So for an example if a highly electronegative atom is bond to a less electronegative atom then there will be a polarity in the molecule and we therefore have the dipole-dipole interaction.

Answer 4

For the determination of geometry for the specific examples you suggest I would use the VSEPR (Valence Shell Electron Pair Repulsion) model and by that determine the geometry.

Answer 5

Thank you!

Answer 6

No problem. If you want some of it expand fx VSEPR just let me know.