To draw the Lewis structure for CO₃²⁻ (carbonate ion) following the octet rule, follow these steps:
- Count the total number of valence electrons: Carbon (C) has 4 valence electrons, and each oxygen (O) has 6 valence electrons. Since the ion has a 2- charge, add 2 more electrons. Total valence electrons = 4 + (3 × 6) + 2 = 24 electrons.
- Place the least electronegative atom in the center: Carbon is less electronegative than oxygen, so it will be the central atom.
- Connect the central atom to the surrounding atoms with single bonds: Draw single bonds between carbon and each oxygen atom. This uses 6 electrons (3 bonds × 2 electrons).
- Distribute the remaining electrons to satisfy the octet rule: Place lone pairs on the oxygen atoms first. Each oxygen needs 6 more electrons to complete its octet. This uses 18 electrons (3 oxygens × 6 electrons).
- Check for formal charges: Ensure that the formal charges are minimized. In this case, the structure with one double bond between carbon and one oxygen (and single bonds to the other two oxygens) is the most stable.
Orbital Overlaps and Bond Types:
- Carbon: Uses sp² hybrid orbitals.
- Oxygen: Uses sp² hybrid orbitals for the sigma bonds and p orbitals for the pi bonds.
Bond Types:
- Sigma (σ) bonds: Formed by the overlap of sp² hybrid orbitals from carbon and oxygen.
- Pi (π) bonds: Formed by the overlap of p orbitals from carbon and oxygen in the double bond.
Total Bond Order:
- Between carbon and the double-bonded oxygen: Bond order = 2 (one sigma and one pi bond).
- Between carbon and each single-bonded oxygen: Bond order = 1 (one sigma bond).