To determine which of the given molecules is a polar molecule, we will analyze each option step by step. We will calculate the total valence electrons, bond pairs, lone pairs, and the molecular geometry to assess polarity.
### Step 1: Analyze BF3
1. **Calculate Valence Electrons**:
- Boron (B) has 3 valence electrons.
- Fluorine (F) has 7 valence electrons, and there are 3 fluorine atoms.
- Total = 3 (B) + 3 × 7 (F) = 3 + 21 = 24 valence electrons.
2. **Calculate Bond Pairs and Lone Pairs**:
- Total valence electrons = 24.
- Divide by 8: 24 ÷ 8 = 3 (bond pairs).
- Remainder = 0, so there are 0 lone pairs.
3. **Determine Geometry**:
- With 3 bond pairs and 0 lone pairs, the geometry is trigonal planar.
4. **Assess Polarity**:
- The molecule is symmetrical (trigonal planar), so BF3 is a non-polar molecule.
### Step 2: Analyze SF4
1. **Calculate Valence Electrons**:
- Sulfur (S) has 6 valence electrons.
- Fluorine (F) has 7 valence electrons, and there are 4 fluorine atoms.
- Total = 6 (S) + 4 × 7 (F) = 6 + 28 = 34 valence electrons.
2. **Calculate Bond Pairs and Lone Pairs**:
- Total valence electrons = 34.
- Divide by 8: 34 ÷ 8 = 4 (bond pairs).
- Remainder = 2, so 2 ÷ 2 = 1 (lone pair).
3. **Determine Geometry**:
- With 4 bond pairs and 1 lone pair, the geometry is seesaw (a variation of trigonal bipyramidal).
4. **Assess Polarity**:
- The presence of a lone pair makes the molecule unsymmetrical, thus SF4 is a polar molecule.
### Step 3: Analyze SiF4
1. **Calculate Valence Electrons**:
- Silicon (Si) has 4 valence electrons.
- Fluorine (F) has 7 valence electrons, and there are 4 fluorine atoms.
- Total = 4 (Si) + 4 × 7 (F) = 4 + 28 = 32 valence electrons.
2. **Calculate Bond Pairs and Lone Pairs**:
- Total valence electrons = 32.
- Divide by 8: 32 ÷ 8 = 4 (bond pairs).
- Remainder = 0, so there are 0 lone pairs.
3. **Determine Geometry**:
- With 4 bond pairs and 0 lone pairs, the geometry is tetrahedral.
4. **Assess Polarity**:
- The molecule is symmetrical (tetrahedral), so SiF4 is a non-polar molecule.
### Step 4: Analyze XeF4
1. **Calculate Valence Electrons**:
- Xenon (Xe) has 8 valence electrons.
- Fluorine (F) has 7 valence electrons, and there are 4 fluorine atoms.
- Total = 8 (Xe) + 4 × 7 (F) = 8 + 28 = 36 valence electrons.
2. **Calculate Bond Pairs and Lone Pairs**:
- Total valence electrons = 36.
- Divide by 8: 36 ÷ 8 = 4 (bond pairs).
- Remainder = 4, so 4 ÷ 2 = 2 (lone pairs).
3. **Determine Geometry**:
- With 4 bond pairs and 2 lone pairs, the geometry is square planar.
4. **Assess Polarity**:
- The molecule is symmetrical (square planar), so XeF4 is a non-polar molecule.
### Conclusion
After analyzing all the options, the only polar molecule among the given choices is **SF4**.
