Question

The `PH_3` molecule can be represented in a tetrahedral arrangement similar to `NH_3`. How does one `PH_3` molecule interact with other `PH_3` molecules?

Answer 1

Hydrogen bonding does not operate in phosphine.........

Explanation:

For the ammonia molecule, there is a large difference in electronegativity between the hydrogen and nitrogen nuclei, and the nitrogen atom polarizes electron density towards itself, `""^(delta-)N-H^(delta+)`. The result? Intermolecular hydrogen bonding operates, which is why the boiling point of ammonia, `-33` `""^@C`, is relatively elevated.

On the other hand, there is not a great of electronegativity difference between the phosphorus atom, and the hydrogen atom. The `P-H` bond is relatively non-polar as a result.

And the consequence? Because of the reduced intermolecular interaction, the boiling point of phosphine is `-87.7` `""^@C`. This is even despite the fact that phosphine is a larger molecule than ammonia, with a larger, more polarizable electron cloud.

And thus dispersion forces only operate in phosphine.