The bond angle in ` PH_3 ` is :

Options

A. Much less than `NH_3`
B. Equal to that of `NH_3`
C. Much greater than `NH_3`
D. Slightly greater than `NH_3`

Answer

A

Explanation

In `NH_3`, there are 3 bonding and 1 lone pair of electrons. The expected geometry is tetrahedral but due to a lone pair of electron the actual geometry is trigonal pyramidal.

The repulsion between lone pair and bond pair of electrons is more than that of between two bond pairs. Thus the bond angles reduced from `109^@28.` (in tetrahedral) to `107^@48.` (i trigonal pyramidal for `NH_3)`.
`PH_3` :
The geometry of `PH_3` is similar to `NH_3`. But the bond pair of electrons are much further away from the central atom due to large size of P atom (Bond length of P – H is more than that of `N - H`). So the lone pair -bond pair repulsion is less than that of in `NH_3`. So due to less repulsion between electrons bond angle in `PH_3` is small than `NH_3`.