Boiling points of hydrogen compounds...?

Question

What would be the pattern in the boiling points for group 15 hydrogen compounds because there's NH3 with -33, and PH3 with -87, AsH3 with -55, and SbH3 with -17? Would it have anything to do with London forces or is it something else?

Answer 1

if you ignore NH3, the trend seen in all the other compounds IS related nearly completely to the differences in their London dispersion forces. NH3 has a very odd boiling point because it can form hydrogen bonds between molecules. These are much stronger and so it is out of line with all the other compounds.