Which of the following molecule has highest dipole moment ?

Question

Accepted Answer

The correct answer is Option 2: NH_3. Let's explore why NH_3 has the highest dipole moment among the given options and why the other molecules have lower dipole moments.

1. **NH_3 (Ammonia):**
   - NH_3 has a trigonal pyramidal shape due to the presence of a lone pair on the nitrogen atom. This lone pair causes a distortion in the geometry, resulting in a net dipole moment.
   - The electronegativity difference between nitrogen and hydrogen creates polar N-H bonds. The vector sum of these bond dipoles, along with the lone pair's contribution, results in a significant net dipole moment.
   - The dipole moment of NH_3 is approximately 1.47 Debye, which is relatively high.

2. **NF_3 (Nitrogen trifluoride):**
   - NF_3 also has a trigonal pyramidal shape, similar to NH_3, but the electronegativity of fluorine is higher than that of nitrogen.
   - The bond dipoles in NF_3 are directed towards the fluorine atoms, which partially cancel out the dipole due to the lone pair on nitrogen, resulting in a lower net dipole moment.
   - The dipole moment of NF_3 is approximately 0.24 Debye, which is much lower than that of NH_3.

3. **BF_3 (Boron trifluoride):**
   - BF_3 has a trigonal planar shape, and the symmetry of the molecule causes the individual bond dipoles to cancel each other out.
   - As a result, BF_3 has no net dipole moment, making it a nonpolar molecule.

4. **CCl_4 (Carbon tetrachloride):**
   - CCl_4 has a tetrahedral shape, and the symmetry of the molecule leads to the cancellation of the individual C-Cl bond dipoles.
   - This results in a net dipole moment of zero, making CCl_4 a nonpolar molecule.

In conclusion, NH_3 has the highest dipole moment among the given options due to its molecular geometry and the presence of a lone pair on nitrogen, which enhances the net dipole moment. The other molecules either have lower dipole moments due to bond dipole cancellation (NF_3) or are nonpolar due to their symmetrical shapes (BF_3 and CCl_4).