Question

Which one of the following molecules has maximum dipole moment ?

• A. $\text{NF}_3$
• B. $\text{CH}_4$
• C. $\text{NH}_3$
• D. $\text{PF}_5$

Answer 1

Answer: (C)

$\text{NH}_3$

Answer 2

Understanding Dipole Moment:

The dipole moment is a measure of the separation of positive and negative charges in a molecule. Molecules with polar bonds and an asymmetrical shape often exhibit a dipole moment. The greater the electronegativity difference between atoms and the asymmetry in the molecule, the higher the dipole moment.

Analyze Each Molecule:

$\text{NF}_3$: Although nitrogen and fluorine have a large electronegativity difference, the structure of $\text{NF}_3$ (trigonal pyramidal) leads to a partial cancellation of the dipole moment due to the lone pair on nitrogen. The net dipole moment of $\text{NF}_3$ is lower than that of $\text{NH}_3$.

$\text{CH}_4$: Methane ($\text{CH}_4$) is a nonpolar molecule with a tetrahedral structure. The dipole moments of the C-H bonds cancel each other out, resulting in a net dipole moment of zero.

$\text{NH}_3$: Ammonia has a trigonal pyramidal structure with a lone pair of electrons on nitrogen. This creates an asymmetrical distribution of charge and a significant net dipole moment. The lone pair on nitrogen intensifies the dipole moment, making $\text{NH}_3$ have a higher dipole moment compared to $\text{NF}_3$.

$\text{PF}_5$: Phosphorus pentafluoride has a trigonal bipyramidal structure, with dipole moments of the axial and equatorial bonds cancelling out. As a result, $\text{PF}_5$ is a nonpolar molecule with a net dipole moment of zero.

Conclusion:

Among the given molecules, $\text{NH}_3$ has the maximum dipole moment due to its trigonal pyramidal structure and the presence of a lone pair on nitrogen, which increases its net dipole moment.