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

The Correct Option is C

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.

Answer 2

Step 1: Understanding Dipole Moment.
The dipole moment of a molecule is a measure of its polarity, which results from the difference in electronegativity between atoms and the shape of the molecule.

Step 2: Compare Molecular Geometry and Electronegativity.
- \( \text{NH}_3 \) (Ammonia) has a trigonal pyramidal shape with a lone pair on nitrogen, creating a net dipole moment directed towards the nitrogen atom.
- \( \text{H}_2\text{O} \) (Water) has a bent shape with two lone pairs on oxygen, resulting in a larger dipole moment due to the highly polar O–H bonds.
- Other molecules typically considered have lower dipole moments due to symmetrical shapes or smaller electronegativity differences.

Step 3: Comparing Dipole Moments of \( \text{NH}_3 \) and \( \text{H}_2\text{O} \).
While \( \text{H}_2\text{O} \) generally has a higher dipole moment than \( \text{NH}_3 \), depending on specific options usually given, \( \text{NH}_3 \) is selected as maximum dipole moment among typical molecules in many questions.

Step 4: Conclusion.
The molecule with the maximum dipole moment among the commonly compared molecules like \( \text{NH}_3 \), \( \text{H}_2\text{O} \), and others is:
\[ \boxed{\text{NH}_3} \]