Which of the following resonance structures for the carbonate ion (CO_3^{2-}), with oxygen as the central atom, is the most stable?

• A. A structure with the central oxygen atom carrying a +1 formal charge and one double bond to carbon.
• B. A structure with the central oxygen atom carrying no formal charge, and all three C–O bonds being equivalent due to delocalization of electrons.
• C. A structure with the central oxygen atom carrying a -2 formal charge and all bonds to carbon being single bonds.
• D. A structure with a double bond between the central oxygen and carbon, and two single bonds to peripheral oxygens, with appropriate lone pairs and formal charges.

Answer: (B)

Verified step by step guidance

1. Step 1: Identify the correct central atom in the carbonate ion (CO_3^{2-}). The carbonate ion has one carbon atom and three oxygen atoms; carbon is the central atom, not oxygen. This is important because resonance structures depend on the correct connectivity of atoms.
2. Step 2: Recall the concept of resonance in polyatomic ions. Resonance structures are different Lewis structures that represent the same molecule, differing only in the placement of electrons (bonds and lone pairs), not the arrangement of atoms.
3. Step 3: Calculate the formal charges for each resonance structure. Use the formula: \(\text{Formal charge} = \text{Valence electrons} - (\text{Nonbonding electrons} + \frac{1}{2} \times \text{Bonding electrons})\). The most stable resonance structure minimizes formal charges and places negative charges on the most electronegative atoms.
4. Step 4: Analyze the resonance structures given, focusing on the placement of charges and bond types. The most stable resonance structure for carbonate has equivalent C–O bonds due to delocalization, with no formal charge on the central atom (carbon), and negative charges distributed on the oxygen atoms.
5. Step 5: Conclude that the resonance structure with carbon as the central atom, no formal charge on carbon, and three equivalent C–O bonds (due to electron delocalization) is the most stable. Structures with oxygen as the central atom or with large formal charges on oxygen are less stable.