How to Draw Molecular Orbital Diagram for CO2

To draw the molecular orbital (MO) diagram for carbon dioxide (CO2), follow these steps:

1. Determine the Total Number of Electrons: Carbon has 4 valence electrons, and each oxygen has 6 valence electrons. Therefore, for CO2, we have:
   • Carbon: 4 electrons
   • Oxygen (2 atoms): 6 x 2 = 12 electrons

   Total = 4 + 12 = 16 electrons.

2. Understand the MO Energy Levels: For diatomic molecules like CO2, the order of energy levels may vary. In general, the order for molecules involving second-period elements is:
   • σ(1s) < sigma*(1s) < σ(2s) < sigma*(2s) < σ(2p) < π(2p) < π*(2p) < σ*(2p)
3. Fill the Molecular Orbitals: Begin filling the molecular orbitals with the total number of electrons you calculated. Fill from the lowest energy level upward, and follow the Pauli exclusion principle and Hund’s rule.
   • Fill σ(1s) with 2 electrons.
   • Fill σ*(1s) with 2 electrons.
   • Fill σ(2s) with 2 electrons.
   • Fill σ*(2s) with 2 electrons.
   • Fill σ(2p) with 2 electrons.
   • Fill π(2p) with 4 electrons (2 in each π orbital).
4. Resulting MO Diagram: After placing all 16 electrons, the sketch of the MO diagram will display filled bonding and antibonding orbitals as follows:
   1. σ(1s) (2 electrons)
   2. σ*(1s) (2 electrons)
   3. σ(2s) (2 electrons)
   4. σ*(2s) (2 electrons)
   5. σ(2p) (2 electrons)
   6. π(2p) (4 electrons)
   7. π*(2p) and σ*(2p) remain unoccupied.

The resulting bond order of CO2 can be calculated as follows:
Bond Order = (Number of Bonding Electrons – Number of Antibonding Electrons) / 2
In this case, the bond order is (10 – 0) / 2 = 5. This indicates a strong double bond character between the carbon and each oxygen atom.

Understanding molecular orbital theory helps explain molecular properties such as stability and magnetism, making it essential in the field of chemistry.