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.
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