[govibe]

1) What is the exact requirements for a hydrogen bond? I know it is a hydrogen bonded to N,O, or F, but does there have to be a lone pair of electrons somewhere? Also, what is a hydrogen bond acceptor and donor

2) When there are dipole-dipole forces, are there also dispersion forces? Is this true for any other forces?

3) When you have molecules that all have similar bonds (dispersion, ion, dipole-dipole), do you then use the formula weight of the molecules to determine the strength of the bond, or do you use the electronegativity difference in the atoms in the molecules?

[Yggdrasil]

1) What is the exact requirements for a hydrogen bond? I know it is a hydrogen bonded to N,O, or F, but does there have to be a lone pair of electrons somewhere? Also, what is a hydrogen bond acceptor and donor

A hydrogen bond acceptor is a N, O, or F with a lone pair.  A hydrogen bond donor is an N, O, or F with a hydrogen attached.  When the hydrogen bond is formed, a weak bond is formed between the hydrogen on the donor and the lone pair on the acceptor.

2) When there are dipole-dipole forces, are there also dispersion forces? Is this true for any other forces?

Yes.  However, since dipole-dipole forces are, in most cases, much stronger than dispersion forces, the dipole-dipole forces are the main contributors to the intermolecular interaction.  This goes for other interactions as well.  When ions interact, there are also dipole-dipole and dispersion forces, but these forces are much weaker than the Coulombic (ionic) forces between the ions and can usually be ignored.

3) When you have molecules that all have similar bonds (dispersion, ion, dipole-dipole), do you then use the formula weight of the molecules to determine the strength of the bond, or do you use the electronegativity difference in the atoms in the molecules?

Can you give an example?

[govibe]

Can you give an example?

Place the following substances in order of increasing volatility.
CH4
CH3Br
CHCl3
CH2Cl2
CH3Cl
CCl4

[Yggdrasil]

Formula weight is the more important difference in this case.  This is why the bp of CH₃Br is 3.56^oC and the bp of CH₃Cl is -24^oC.  If electronegativity difference were the dominant factor, then you would expect CH₃Cl to have the higher boiling point since the electronegativity difference between C and Cl is greater than the difference between C and Br.

[govibe]

so when do you know to use electronegativity difference versus difference in atomic weights to distinguish which IM forces are strongest (for the same types of forces)

[Yggdrasil]

I would say that you should use atomic weight over electronegativity difference in almost all cases.

[govibe]

^even when finding strength of ion-ion bonds? Also, doesn't polarizability have something to do with atomic size?