Why does NH3 have a boiling point of -33 C while PH3 has a boiling point of -87 C?

Question

the question is why NH3 has a boiling point of -33 C which is higher than PH3 (-87C)? Has to be explained in terms of intermolecular forces but i cant find the answer anywhere, i need to know this, it has a lot of marks on my exam i'm studying for.

Answer 1

Since nitrogen has a high electronegativity compounds containing N-H bonds (like those containing O-H or F-H bonds) will exhibit hydrogen bonding, which is a much stronger intermolecular force than the 'normal' dipole-dipole interaction in PH3.

Answer 2

NH3 has partial charges, since Nitrogen is more electronegative than hydrogen. In each molecule, this leaves nitrogen slightly negative, and each hydrogen slightly negative, allowing for the formation of weak hydrogen bonds between molecules (much weaker than water, since the boiling point is much lower)

Phosphine cannot form hydrogen bonds, and thus the only intermolecular forces are dispersion forces, which are much weaker.

Hope this answers your question.

Answer 3

N is highly electronegative. it can form h-bonds between its molecules. this strong h-bonds require more energy to overcome. hence it has a higher boiling point compared to ph3, which are held together by weaker van der waals forces.