Which of the following statements regarding bond angles in the given molecules is correct?
Which of the following statements regarding bond angles in the given molecules is correct?
$\mathrm{NF}_{3}>\mathrm{NH}_{3}$ and $\mathrm{OF}_{2}>\mathrm{OH}_{2}$
$\mathrm{NF}_{3}>\mathrm{NH}_{3}$ and $\mathrm{OF}_{2} < \mathrm{OH}_{2}$
$\mathrm{NF}_{3} < \mathrm{NH}_{3}$ and $\mathrm{OF}_{2}>\mathrm{OH}_{2}$
$\mathrm{NF}_{3} < \mathrm{NH}_{3}$ and $\mathrm{OF}_{2} < \mathrm{OH}_{2}$
Solution
Bond angle in $\mathrm{NF}_{3}$ is smaller than in $\mathrm{NH}_{3}$. Also bond angle in $\mathrm{OF}_{2}$ is smaller than in $\mathrm{OH}_{2}$. This is primarily due to ionicity of $\mathrm{N}-\mathrm{F}$ and $\mathrm{O}-\mathrm{F}$ bonds. The more electronegative fluorine atoms attract bonding electorn pairs away from $\mathrm{N}$ and $\mathrm{O}$ nuclei. This causes expansion of lone pair causing bond angles $\mathrm{F}-\mathrm{N}-\mathrm{F}$ and $\mathrm{F}-\mathrm{O}-\mathrm{F}$ smaller than those in $\mathrm{H}-\mathrm{N}-\mathrm{H}$ and $\mathrm{H}-\mathrm{O}-\mathrm{H}$. Experimental values are: $\mathrm{NF}_{3}\left(102.3^{\circ}ight), \mathrm{NH}_{3}\left(107.2^{\circ}ight), \mathrm{OF}_{2}$ $\left(103.1^{\circ}ight)$ and $\mathrm{OH}_{2}\left(104.5^{\circ}ight)$
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