Which of the following is a the most preferred and hence of the lower energy for `SO_(3)`?

Options

A.
B.
C.
D.

Answer

To determine the most preferred structure of sulfur trioxide (SO₃) with the lowest energy, we need to calculate the formal charges of the different resonance structures. Here’s a step-by-step solution:

### Step 1: Identify the Valence Electrons
- **Sulfur (S)** has 6 valence electrons.
- **Oxygen (O)** has 6 valence electrons, and there are three oxygen atoms in SO₃, contributing a total of 18 valence electrons from oxygen.

**Total valence electrons in SO₃ = 6 (from S) + 18 (from 3 O) = 24 valence electrons.**

### Step 2: Draw Possible Structures
1. **First Structure**:
- Sulfur is bonded to three oxygen atoms with single bonds, and each oxygen has three lone pairs.

2. **Second Structure**:
- Sulfur is bonded to three oxygen atoms with double bonds, and each oxygen has two lone pairs.

### Step 3: Calculate Formal Charges
**For the first structure**:
- **Oxygen**:
- Valence electrons = 6
- Non-bonding electrons = 6 (3 lone pairs)
- Bonding electrons = 2 (1 bond)

Formal Charge (FC) = 6 - 6 - (1/2 * 2) = 6 - 6 - 1 = -1

- **Sulfur**:
- Valence electrons = 6
- Non-bonding electrons = 0
- Bonding electrons = 8 (4 bonds)

FC = 6 - 0 - (1/2 * 8) = 6 - 0 - 4 = +2

**Total formal charges for the first structure**:
- Sulfur = +2, each oxygen = -1 (total of -3 from three oxygens)

**For the second structure**:
- **Oxygen**:
- Valence electrons = 6
- Non-bonding electrons = 4 (2 lone pairs)
- Bonding electrons = 4 (2 bonds)

FC = 6 - 4 - (1/2 * 4) = 6 - 4 - 2 = 0

- **Sulfur**:
- Valence electrons = 6
- Non-bonding electrons = 0
- Bonding electrons = 12 (6 bonds)

FC = 6 - 0 - (1/2 * 12) = 6 - 0 - 6 = 0

**Total formal charges for the second structure**:
- Sulfur = 0, each oxygen = 0 (total of 0)

### Step 4: Compare Formal Charges
- The first structure has formal charges of +2 on sulfur and -1 on each oxygen, which indicates a higher energy state due to the presence of charges.
- The second structure has all formal charges equal to zero, indicating a more stable and lower energy configuration.

### Conclusion
The second structure (with sulfur double bonded to each oxygen) is the most preferred structure for SO₃, as it has the lowest energy due to minimized formal charges.

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