Question

Discuss the important characteristics of the hydrides of group 15 elements.

Answer 1

1) Thermal stability: As the element moves down the group, the group 15 element hydrides lose thermal stability. BiH₃ has only been found in traces and is highly unstable.

NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃

2) Basic character: The hydrides of group 15 elements act as Lewis bases because the core atom has a single pair of electrons. The strongest of these bases is ammonia. As one moves down the group, the hydrides of group 15 elements lose their basic strength. PH₃ is a far weaker base than NH₃, which is clearly basic. AsH₃, SbH3, and BiH₃ do not show any basic properties.

3) Reducing character: As the hydrides of group 15 elements transition from NH₃ to BiH₃, their lowering character rises. The reducing nature of these hydrides follows:

NH₃ < PH₃ < AsH₃ < SbH₃ < BiH₃

4) Tendency to form hydrogen bonding: Ammonia is the only hydride of group 15 elements that can create intermolecular hydrogen bonds with both water molecules and itself. The existence of hydrogen bonding leads to the association of a large number of ammonia molecules in its liquid state. The other hydrides show practically no tendency to form hydrogen bonding.

5) Boiling point: Compared to phosphine, ammonia has a greater boiling point. When moving from AsH₃ to BiH₃, the boiling points rise.