Question

In the Lewis dot structure of carbonate ion ($ \text{CO}_3^{2-} $), what are the formal charges on oxygen atoms 1, 2, and 3 respectively?

• A. \(-2, 0, 0\)
• B. \(-1, 0, -1\)
• C. \(0, -1, -1\)
• D. \(-3, 0, +1\)

Hint:

In polyatomic ions, formal charge helps explain resonance. Double bonded O has 0 FC, single bonded O has –1.

Answer 1

The Correct Option is B

In \( \text{CO}_3^{2-} \), the resonance hybrid shows:
- One oxygen atom forms a double bond with carbon → formal charge = 0
- Two oxygen atoms with single bonds and lone pairs → formal charge = –1
Hence: - O\(_1\): –1
- O\(_2\): 0 (double bonded)
- O\(_3\): –1
Formal charge calculation (FC): \[ \text{FC} = (\text{Valence electrons}) - (\text{Lone pair electrons}) - \frac{1}{2}(\text{Bonding electrons}) \]