Question

Which molecule has a net dipole moment of zero among \(NH_3\), \(H_2O\), \(NF_3\), and \(CCl_4\)?

• A. \(NH_3\)
• B. \(H_2O\)
• C. \(NF_3\)
• D. \(CCl_4\)

Hint:

Highly symmetrical molecules such as \(CO_2\), \(BF_3\), and \(CCl_4\) often have zero dipole moment because individual bond dipoles cancel out.

Answer 1

The Correct Option is D

Concept: Dipole moment is a measure of the separation of positive and negative charges in a molecule. The overall dipole moment depends on both bond polarity and molecular geometry. If the bond dipoles cancel each other due to symmetry, the molecule has zero net dipole moment.

Step 1: Examine molecular shapes.

• \(NH_3\): Trigonal pyramidal shape due to one lone pair on nitrogen.
• \(H_2O\): Bent or V-shaped geometry due to two lone pairs on oxygen.
• \(NF_3\): Trigonal pyramidal geometry similar to ammonia.
• \(CCl_4\): Tetrahedral and highly symmetrical.

Step 2: Effect of symmetry on dipole moment.
In \(CCl_4\), four identical \(C{-}Cl\) bonds are arranged symmetrically around the carbon atom in a tetrahedral geometry. The dipole moments of these bonds cancel each other. \[ \mu_{\text{net}} = 0 \]

Step 3: Conclusion.
Since the bond dipoles cancel perfectly in \(CCl_4\), it has zero net dipole moment.