Question

Arrange the following molecules in decreasing order of their dipole moments:
${H}_2{O}, {NF}_3, {H}_2{S}, {NH}_3$

• A. ${H}_2{O}>{NF}_3>{H}_2{S}>{NH}_3$
• B. ${NF}_3>{H}_2{O}>{H}_2{S}>{NH}_3$
• C. ${NF}_3>{H}_2{O}>{NH}_3>{H}_2{S}$
• D. ${H}_2{O}>{NH}_3>{H}_2{S}>{NF}_3$

Hint:

Dipole moments are influenced by both the electronegativity of atoms and the molecular geometry. Molecules with higher asymmetry and greater electronegativity differences tend to have higher dipole moments.

Answer 1

The Correct Option is D

The dipole moment depends on the electronegativity difference and the molecular geometry. Here’s the analysis:

• H₂O: High dipole moment due to the bent shape and significant electronegativity difference between oxygen and hydrogen.
• NH₃: High dipole moment due to the trigonal pyramidal shape and electronegativity difference between nitrogen and hydrogen.
• H₂S: Lower dipole moment than H₂O due to less electronegativity difference and similar bent shape.
• NF₃: Lower dipole moment due to the trigonal pyramidal shape and the opposing dipole moments of the N-F bonds partially canceling each other.

Thus, the decreasing order of dipole moments is:

$${H}_2{O} > {NH}_3 > {H}_2{S} > {NF}_3$$

Final Answer:
${H}_2{O} > {NH}_3 > {H}_2{S} > {NF}_3$