Question

Which of the following is incorrect order of $X-P-X$ bond angle?

• A. $PB{r}_3>PC{l}_3>P{F}_3$
• B. $POB{r}_3>POC{l}_3>PO{F}_3$
• C. $PB{r}_4^{+}>PC{l}_4^{+}>P{F}_4^{+}$
• D. $PC{l}_4^{+}>PC{l}_3$

Answer 1

The correct option is C $PB{r}_4^{+}>PC{l}_4^{+}>P{F}_4^{+}$

a) The $X-P-X$ bond angle follows the order $PB{r}_3>PC{l}_3>P{F}_3$, because as electronegativity decreases from $F$ to $Br$, bond pair- bond pair repulsion will increase in the manner $PB{r}_3>PC{l}_3>P{F}_3$.
b) Due to the same reason $X-P-X$ bond angle in $POB{r}_3$, $POC{l}_3$ and $PO{F}_3$ follows the order $POB{r}_3>POC{l}_3>PO{F}_3$
c) Since all the $PB{r}_4^{+},PC{l}_4^{+},P{F}_4^{+}$ have the tetrahedral geometry so bond angles are equal.
d) Though both $PC{l}_4^{+}$ and $PC{l}_3$ have $s{p}^3$ hybridisation, but due to presence of a lone pair in $PC{l}_3$, there will be some lone pair-bond pair repulsion, which decreases the bond angle of $PC{l}_3$ from the ideal bond angle (${109.5}^0$).