Question

In the Lewis dot structure of carbonate ion shown under, the formal charges on the oxygen atoms \(1,2\) and \(3\) are respectively:

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

Hint:

In carbonate ion \((CO_3^{2-})\), the oxygen atom forming a double bond with carbon has zero formal charge, while each singly bonded oxygen carries a \(-1\) formal charge.

Answer 1

The Correct Option is B

Step 1: Recall the Lewis resonance structure of carbonate ion $CO_3^{2-}$.
In one resonance structure, C forms a double bond with O2, and single bonds with O1 and O3. O1 and O3 each carry a negative formal charge.
Step 2: Recall the formal charge formula.
\[ \text{FC} = \text{Valence electrons} - \text{Non-bonding electrons} - \frac{\text{Bonding electrons}}{2} \] For oxygen: valence electrons = 6.
Step 3: Calculate FC on O2 (doubly bonded to C).
O2 has a double bond: bonding e = 4, non-bonding e = 4. \[ FC = 6 - 4 - \frac{4}{2} = 0 \]
Step 4: Calculate FC on O1 and O3 (singly bonded to C).
Each has a single bond: bonding e = 2, non-bonding e = 6. \[ FC = 6 - 6 - \frac{2}{2} = -1 \]
Step 5: Verify total formal charge.
Total FC = $(-1) + 0 + (-1) = -2$. This matches the charge of $CO_3^{2-}$.
Step 6: State the formal charges on O1, O2, O3.
\[ \boxed{-1,\ 0,\ -1} \]