Question

Which of the following is the incorrect order of dipole moment?

• A. $\mathrm{HF}>\mathrm{HCl}>\mathrm{HBr}$
• B. ${\mathrm{NH}}_3>{\mathrm{NCl}}_3>{\mathrm{NF}}_3$
• C. ${\mathrm{NH}}_3>{\mathrm{NF}}_3>{\mathrm{NCl}}_3$
• D. ${\mathrm{CH}}_3\mathrm{Cl}>{\mathrm{CH}}_3\mathrm{F}>{\mathrm{CH}}_3\mathrm{Br}$

Answer 1

The correct option is C

${\mathrm{NH}}_3>{\mathrm{NF}}_3>{\mathrm{NCl}}_3$

Explanation of the correct option:

C. ${\mathrm{NH}}_3>{\mathrm{NF}}_3>{\mathrm{NCl}}_3$

• In ${\mathrm{NH}}_3$ , $\mathrm{N}$ is more electronegative than H, so the bond in $\mathrm{N}-\mathrm{H}$ dipole moment is from $\mathrm{H}$ to $\mathrm{N}$ and in case of ${\mathrm{NF}}_3$, $\mathrm{F}$ is more electronegative than $\mathrm{N}$, so electron will move from $\mathrm{N}$ to $\mathrm{F}$and in ${\mathrm{NCl}}_3$,$\mathrm{Cl}$ is more electronegative than $\mathrm{N}$ so electron will move from $\mathrm{N}$ to $\mathrm{Cl}$, but $\mathrm{Cl}$ electronegativity is less than $\mathrm{F}$.

Explanation of the incorrect options:

A: $\mathrm{HF}>\mathrm{HCl}>\mathrm{HBr}$

• As $\mathrm{F}$ is a more electronegative element than $\mathrm{Cl}$ and $\mathrm{Br}$.
• So the order of arrangement is correct for the dipole moment.

B: ${\mathrm{NH}}_3>{\mathrm{NCl}}_3>{\mathrm{NF}}_3$

• In case of ${\mathrm{NH}}_3$ > ${\mathrm{NCl}}_3$ > ${\mathrm{NF}}_3$, ${\mathrm{NH}}_3$ electrons will move from $\mathrm{H}$ to $\mathrm{N}$.
• ${\mathrm{NCl}}_3$ dipole moment is more than ${\mathrm{NF}}_3$, because in ${\mathrm{NCl}}_3$ bond pair-bond pair repulsion is more, so its bond angle is also more than ${\mathrm{NF}}_3$.

D: ${\mathrm{CH}}_3\mathrm{Cl}>{\mathrm{CH}}_3\mathrm{F}>{\mathrm{CH}}_3\mathrm{Br}$

• In ${\mathrm{CH}}_3\mathrm{Cl}$ > ${\mathrm{CH}}_3\mathrm{F}$ > ${\mathrm{CH}}_3\mathrm{Br}$, in ${\mathrm{CH}}_3\mathrm{Cl}$ the $\mathrm{C}-\mathrm{Cl}$bond length is greater than $\mathrm{C}-\mathrm{F}$ bond length.
• Because of this, the separation of charges is more in ${\mathrm{CH}}_3\mathrm{Cl}$ as a result of which dipole moment is more in ${\mathrm{CH}}_3\mathrm{Cl}$ than ${\mathrm{CH}}_3\mathrm{F}$.
• $\mathrm{Br}$ is less electronegative than $\mathrm{F},\mathrm{Cl}$ so its dipole moment is also less.

Hence, the correct option is C i.e. the incorrect order of dipole moment is ${\mathrm{NH}}_3$ > ${\mathrm{NF}}_3$ > ${\mathrm{NCl}}_3$