Which of the given compound have a permanent dipole moment ?

Options

A. `X_eF_4`
B. `SiF_4`
C. `BF_3`
D. `SF_4`

Answer

To determine which of the given compounds have a permanent dipole moment, we need to analyze the molecular geometry and hybridization of each compound. A permanent dipole moment occurs in molecules that are asymmetrical and have polar bonds. Here’s a step-by-step solution:

### Step 1: Understand the Concept of Dipole Moment
A dipole moment arises in a molecule when there is a separation of charge due to differences in electronegativity between bonded atoms. For a molecule to have a permanent dipole moment, it must be asymmetrical in shape, and the bonds must be polar.

**Hint:** Remember that symmetrical molecules, even if they have polar bonds, may have dipole moments that cancel each other out.

### Step 2: Identify the Hybridization
To analyze the compounds, we first need to determine their hybridization based on the number of bond pairs and lone pairs.

1. **XeF4**:
- Valence electrons: Xe has 8, F has 1 each (4 F atoms contribute 4).
- Total: 8 + 4 = 12 electrons.
- Bond pairs: 4 (Xe-F).
- Lone pairs: 2 (on Xe).
- Hybridization: sp³d² (octahedral geometry).
- Geometry: Symmetrical (due to lone pairs opposite each other).
- **Dipole Moment**: 0 (symmetrical).

2. **SiF4**:
- Valence electrons: Si has 4, F has 1 each (4 F atoms contribute 4).
- Total: 4 + 4 = 8 electrons.
- Bond pairs: 4 (Si-F).
- Lone pairs: 0.
- Hybridization: sp³ (tetrahedral geometry).
- Geometry: Symmetrical.
- **Dipole Moment**: 0 (symmetrical).

3. **BF3**:
- Valence electrons: B has 3, F has 1 each (3 F atoms contribute 3).
- Total: 3 + 3 = 6 electrons.
- Bond pairs: 3 (B-F).
- Lone pairs: 0.
- Hybridization: sp² (trigonal planar geometry).
- Geometry: Symmetrical.
- **Dipole Moment**: 0 (symmetrical).

4. **AsF3** (assuming it's part of the question):
- Valence electrons: As has 5, F has 1 each (3 F atoms contribute 3).
- Total: 5 + 3 = 8 electrons.
- Bond pairs: 3 (As-F).
- Lone pairs: 1 (on As).
- Hybridization: sp³ (trigonal pyramidal geometry).
- Geometry: Asymmetrical.
- **Dipole Moment**: Yes (asymmetrical).

### Step 3: Conclusion
Based on the analysis, the compounds that have a permanent dipole moment are those that are asymmetrical and have polar bonds. In this case, **only AsF3** has a permanent dipole moment.

### Final Answer
The compound with a permanent dipole moment is **AsF3**.