Write a note on hydrides of group VA. Also explain why basicity of these hydrides increase down the group.
Answers
Answer:
The reducing character of hydrides of group 15 elements increases from top to bottom because the E-H strength (Here E= N, P, As, Sb, or Br) bond decreases down the group due to an increase in the size of the central atom.
Reason
The stability of hydrides decreases down the group from NH3 to BiH3. This is due to a decrease in their bond dissociation enthalpy. Reducing character is directly related to the ease of losing hydrogen. NH3 is a mild reducing agent, and BiH3 has the strongest reducing character amongst all hydrides of group 15.
The trend of group 15 hydride based on reducing character is as given below.
BiH3 > SbH3 > AsH3 > PH3 > NH3
Stability decreases down the group as the bond dissociation energy decreases.
Hence, the bond dissociation energy decreases down the group due to the increase in the central atom size.
The hydrides of these elements are pyramidal with a lone pair of electrons in one of the orbitals. The bond angles gradually decrease due to a decrease in bond pair-bond pair repulsion on moving down the group.