# According to VSEPR theory, what is the shape of the PH_3 molecule best described as?

Oct 8, 2016

The shape of phosphine is $\text{pyramidal}$; i.e. it is an analogue of ammonia.

#### Explanation:

There are $5 + 3$ valence electrons for which to account; and this gives 4 electron pairs arranged the central phosphorus atom. These assume a tetrahedral geometry, however, one of the arms of the tetrahedron is a lone pair, and geometry descends to trigonal pyramidal with respect to phosphorus.

The $\angle H - P - H$ $\cong$ 94""^@, whereas that for /_H-N-H~=105""^@. This difference in bond angles between the homologues is not readily rationalized, and beyond the scope of even a third year inorganic chemist. This bond angle discrepancy is also observed for ${H}_{2} S$ versus ${H}_{2} O$.

So, the shape is PYRAMIDAL :

Hope it Helps :)