Which of the following compound has least dipole moment ?

Options

A. `PH_3`
B. `CHCl_3`
C. `NH_3`
D. `BF_3`

Answer

To determine which compound has the least dipole moment among the given options, we will analyze the polarity of each compound step by step.

### Step 1: Understand Dipole Moment
Dipole moment is a measure of the polarity of a chemical bond. It occurs due to the difference in electronegativity between the atoms involved in a bond. A molecule with a net dipole moment is considered polar, while a molecule with no net dipole moment is non-polar.

**Hint:** Remember that the dipole moment depends on both the electronegativity of the atoms and the molecular geometry.

### Step 2: Analyze Each Compound
1. **PH3 (Phosphine)**
- Phosphorus (P) has 5 valence electrons and forms three bonds with hydrogen (H), leaving one lone pair.
- The bond dipoles from P-H bonds point towards the more electronegative hydrogen atoms, and the lone pair contributes to the overall dipole moment.
- Result: PH3 is a polar molecule.

2. **CHCl3 (Chloroform)**
- Carbon (C) forms one bond with hydrogen and three bonds with chlorine (Cl).
- The bond dipoles from C-H and C-Cl bonds will not cancel out due to the presence of three Cl atoms, which are more electronegative than C.
- Result: CHCl3 is a polar molecule.

3. **NH3 (Ammonia)**
- Nitrogen (N) forms three bonds with hydrogen and has one lone pair.
- The bond dipoles from N-H bonds point towards the nitrogen, and the lone pair also contributes to the dipole moment.
- Result: NH3 is a polar molecule.

4. **BF3 (Boron Trifluoride)**
- Boron (B) forms three bonds with fluorine (F) in a trigonal planar geometry.
- The bond dipoles from B-F bonds point towards the more electronegative fluorine atoms.
- Due to the symmetrical arrangement, the dipoles cancel each other out.
- Result: BF3 is a non-polar molecule with a net dipole moment of zero.

### Step 3: Compare Dipole Moments
- PH3, CHCl3, and NH3 are all polar molecules and will have non-zero dipole moments.
- BF3 is a non-polar molecule with a dipole moment of zero.

### Conclusion
The compound with the least dipole moment is **BF3**, as it has a dipole moment of zero.

**Final Answer:** BF3 (Boron Trifluoride) has the least dipole moment.

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