Question

Which of the following is the most polar compound?

• A. ${\mathrm{NH}}_3$
• B. ${\mathrm{BiH}}_3$
• C. ${\mathrm{AsH}}_3$
• D. ${\mathrm{SbH}}_3$

Answer 1

The correct option is A

${\mathrm{NH}}_3$

Explanation of the correct option:

(A)${\mathrm{NH}}_3$

• There is a large difference in electronegativity between $\mathrm{N}$ and $\mathrm{H}$.
• Since nitrogen's valence shell has five electrons, it has to interact with three hydrogen atoms.
• As ${\mathrm{NH}}_3$has three Nitrogen- Hydrogen bond dipoles that do not cancel out.
• ${\mathrm{NH}}_3$ is the most polar compound.

Explanation of the incorrect options:

(B)${\mathrm{BiO}}_3$

• $\mathrm{Bi}$ is an electronegative element whose valency is 3.
• Its electronic configuration is $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}6{\mathrm{s}}^{2}6{\mathrm{p}}^3$, so it has many shells of electrons around the nucleus.
• Because of that $\mathrm{Bi}$ can not attract outside electrons from $\mathrm{O}$ with a large force.
• ${\mathrm{BiO}}_3$ is a polar compound but its polarity is not so high as ${\mathrm{NH}}_3$.

(C)${\mathrm{AsH}}_3$

• ${\mathrm{AsH}}_3$ contains 3 polar bonds and one lone pair and this lone pair distorts the geometry.
• The dipole moment vectors do not cancel out in the resultant trigonal pyramidal shape.
• As the electronegativity of $\mathrm{As}$ is less than $\mathrm{N}$.
• So ${\mathrm{AsH}}_3$is a polar compound, but its polarity is less than ${\mathrm{NH}}_3$.

(D) ${\mathrm{SbH}}_3$

• The size $\mathrm{Sb}$ is larger and it contains many shells around the nucleus.
• Because of this $\mathrm{Sb}$ is less electronegative than $\mathrm{N}$.
• ${\mathrm{SbH}}_3$ has induced dipole-induced dipole force.
• ${\mathrm{SbH}}_3$ is a polar compound but its polarity is less than ${\mathrm{NH}}_3$.

Hence, option (A) is correct. ${\mathrm{NH}}_3$ is the most polar compound.