Question

Which gas has the greater degree of intermolecular force: ammonia, `NH_3(g)`; or phosphine, `PH_3(g)`?

Answer 1

Phosphine, `"b.p. "-87.7` `""^@C`; ammonia, `"b.p. "-33.3` `""^@C`;

Explanation:

Given the boiling points, CLEARLY, ammonia, `NH_3`, has the greatest degree of intermolecular bonding. How do we rationalize this? The obvious discriminant is hydrogen bonding. There is little electronegativity difference between phosphorus and hydrogen, and yet a large difference exists between nitrogen and hydrogen.

The `N-H` bond is strongly polar on this account. The result is that the ammonia participates in intermolecular hydrogen bonding, which is a potent intermolecular force.