Q10.35P - Chemistry: Molecular Nature Of Matter And Change

Question

Determine the electron-group arrangement, molecular shape, and ideal bond angle(s) for each of the following:

(a)  ${\mathbf{SO}}_4^{2-}$

(b)  ${\mathbf{NO}}_2^{-}$

(c)  ${\mathbf{PH}}_3$

Step-by-Step Solution

Answer

The shapes and bond angles of molecules can be determined from the VSEPR theory. The deviations arise mainly due to lone pair-lone pair repulsions.

Step 1: SO 4 2 -

The shape of the molecule is Tetrahedral. The central sulphur atom is sp³ hybridized with an expected bond angle of $\mathbf{109}\mathbf{.}{\mathbf{5}}^o$. However, lone pair-bond pair repulsion on sulphur reduces the bond angle from the expected value. 

Step 2: NO 2 -

The molecule has a bent or V-shaped shape. The nitrogen atom is sp³ hybridized with an expected bond angle of ${\mathbf{120}}^o$^. The lone pair on nitrogen reduces the bond angle from the expected value.

Step 3: PH 3

The shape of the molecule is Pyramidal. The phosphrous atom is sp³ hybridized with expected bond angle of $\mathbf{109}\mathbf{.}{\mathbf{5}}^o$. However, the lone pair on phosphorous reduces the bond angle from the expected value.