The correct lewis structure of CO32- ion

The correct lewis structure of CO32- ion

The Correct Answer and Explanation is:

Correct Lewis Structure for CO₃²⁻ (Carbonate Ion):

The correct Lewis structure for the carbonate ion CO₃²⁻ is:

mathematicaCopyEdit      O
     //
C — O⁻
     \
      O⁻

Or more symmetrically, to show resonance:

mathematicaCopyEdit     O⁻        O        O⁻
      \\      ||       //
        C    ↔   C    ↔   C
      /        \\       /
     O         O⁻     O

This means the ion has three resonance structures, each with a double bond to one oxygen and single bonds to the other two, each carrying a negative charge.

Explanation

The carbonate ion (CO₃²⁻) consists of one carbon atom and three oxygen atoms, with an overall charge of minus two. To draw its Lewis structure, we begin by calculating the total number of valence electrons.

• Carbon has 4 valence electrons.
• Each oxygen atom has 6 valence electrons.
• The ion has a 2− charge, meaning we add 2 electrons.

Total valence electrons:
= 1(C × 4) + 3(O × 6) + 2(extra electrons)
= 4 + 18 + 2
= 24 valence electrons

Step 1: Place carbon in the center, and attach three oxygen atoms around it using single bonds. Each single bond uses 2 electrons, totaling 6 electrons.

Step 2: Distribute the remaining 18 electrons as lone pairs on the oxygens to complete their octets.

Step 3: Now, carbon only has 6 electrons. To complete its octet, one of the single bonds must become a double bond. This is done by converting a lone pair from one of the oxygens into a bonding pair.

Step 4: After creating a double bond between carbon and one oxygen, carbon has 8 electrons. Two oxygens now have single bonds and carry a negative charge each.

Since any of the three oxygen atoms can form the double bond, there are three resonance structures. These structures contribute equally, meaning the actual structure is a resonance hybrid. The bond lengths in the carbonate ion are identical and intermediate between single and double bonds.

This resonance stabilizes the ion and helps explain its chemistry and geometry. The structure is trigonal planar, and the bond angles are approximately 120 degrees.