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 formula for formal charge.
Formal charge is calculated using \[ \text{Formal charge} = \text{Valence electrons} - \text{Non-bonding electrons} - \frac{1}{2} (\text{Bonding electrons}) \] For oxygen, \[ \text{Valence electrons}=6 \]

Step 2: Find the formal charge on oxygen atom \(2\).
Oxygen atom \(2\) is double bonded to carbon.
It has: \[ 4 \text{ non-bonding electrons} \] and \[ 4 \text{ bonding electrons} \] Therefore, \[ \text{Formal charge} = 6-4-\frac{4}{2} \] \[ =6-4-2 \] \[ =0 \] Thus, oxygen atom \(2\) has formal charge \[ 0 \]

Step 3: Find the formal charge on oxygen atoms \(1\) and \(3\).
Oxygen atoms \(1\) and \(3\) are single bonded to carbon.
Each oxygen has: \[ 6 \text{ non-bonding electrons} \] and \[ 2 \text{ bonding electrons} \] Therefore, \[ \text{Formal charge} = 6-6-\frac{2}{2} \] \[ =6-6-1 \] \[ =-1 \] Thus, both oxygen atoms \(1\) and \(3\) carry \[ -1 \] formal charge.

Step 4: Final conclusion.
Hence, the formal charges on oxygen atoms \(1,2,3\) respectively are \[ \boxed{-1,0,-1} \]