Question

Assign a reason for each of the following statements :
(i) Ammonia is a stronger base than phosphine.
(ii) Sulphur in vapour state exhibits a paramagnetic behaviour.

Answer 1

(i) Due to the presence of lone pair of electrons on the central atom both `NH_(3)` and `PH_(3)` are Lewis Bases. When `NH_(3)` or `PH_(3)` accepts a proton, an additional N-H or P-H bond is formed.
`H_(3)N : + H^(+) rarrNH_(4)^(+), H_(3)P : + H^(+) rarrPH_(4)^(+)`
Due to smaller size of N than P, N-H bond thus formed is much stronger than P-H bond. As a result `NH_(3)` has more tendency than `PH_(3)` to accept a proton. Therefore, `NH_(3)` is stronger base than `PH_(3)`.
(ii) In vapour state sulphur partly exists as `S_(2)` molecule which has two unpaired electrons is the artibonding `pi**` orbitals like `O_(2)` and hence, exhibits paramagnetism.