# Sulfur Dioxide (SO2) Formal Charge

In sulfur dioxide (SO_{2}), sulfur (S) has a double covalent bond with one oxygen (O) atom and a single covalent bond with another. SO_{2} undergoes the following resonance.

O^{–}–S^{+}=O ↔ O=S^{+}–O^{–}

Let us calculate the formal charge of both these structures.

## i. O^{–}–S^{+}=O

V = 6, N = 2, B = 6

Therefore,

q_{f} = 6 – 2 – 6/2 = 1

**Oxygen 1**

V = 6, N = 6, B = 2

Therefore,

q_{f} = 6 – 6 – 2/2 = -1

**Oxygen 2**

V = 6, N = 4, B = 4

Therefore,

q_{f} = 6 – 4 – 4/2 = 0

The net formal charge is: 1 – 1 + 0 = 0

## ii. O=S^{+}–O^{–}

**Sulfur**

V = 6, N = 2, B = 6

Therefore,

q_{f} = 6 – 2 – 6/2 = 1

**Oxygen 1**

V = 6, N = 4, B = 4

Therefore,

q_{f} = 6 – 4 – 4/2 = 0

**Oxygen 2**

V = 6, N = 6, B = 2

Therefore,

q_{f} = 6 – 6 – 2/2 = -1

The net formal charge is: 1 + 0 – 1 = 0

The formal charge of SO_{2} is zero. It spends half its time in each of its two resonance structures. It flips back and forth swiftly between the two forms.