CHEMICAL BONDING Drawing the MO energy diagram for a Period 2 homodiatom Draw the molecular orbital (MO) electron diagram for the C2 molecule: Be sure your diagram contains all of the electrons in the molecule, including any core electrons.

CHEMICAL BONDING Drawing the MO energy diagram for a Period 2 homodiatom Draw the molecular orbital (MO) electron diagram for the C2 molecule: Be sure your diagram contains all of the electrons in the molecule, including any core electrons. Energy

The Correct Answer and Explanation is:

✅ MO Energy Diagram for C₂ (Carbon Dimer)

scssCopyEdit                            σ*(2p)
                            ↑   ↑
                        π*(2p) π*(2p)
                        ↑   ↑
                        π(2p)  π(2p)
                        ↑   ↑
                            σ(2p)
                            ↑
                          σ*(2s)
                          ↑   ↑
                          σ(2s)
                          ↑   ↑
Carbon Atom 1                        Carbon Atom 2

• Total electrons in C₂ = 12 (6 from each carbon)
• Electron configuration: 1s² 2s² 2p² for each carbon
• Core electrons (1s) typically not shown in MO diagrams, but if needed:
  • σ(1s) → 2 electrons
  • σ*(1s) → 2 electrons

So including core electrons:

scssCopyEditσ(1s)      ↑↓  
σ*(1s)     ↑↓  
σ(2s)      ↑↓  
σ*(2s)     ↑↓  
π(2p)      ↑↓  ↑↓  
π*(2p)     (empty)  
σ(2p)      (empty)

---

🧪 Explanation

The molecular orbital (MO) theory explains bonding by combining atomic orbitals to form molecular orbitals. In the case of C₂, which consists of two carbon atoms (atomic number 6), each contributes 6 electrons for a total of 12.

These electrons fill molecular orbitals in a specific order. For Period 2 homonuclear diatomic molecules like B₂, C₂, and N₂, the correct MO ordering (due to s-p mixing) is:

σ(1s) < σ(1s) < σ(2s) < σ(2s) < π(2p) < σ(2p) < π*(2p) < σ*(2p)**

This order changes in O₂ and F₂, where the σ(2p) drops below π(2p) due to reduced s-p mixing.

For C₂:

• The first 4 electrons go into σ(1s) and σ*(1s) orbitals (core).
• The next 4 electrons fill σ(2s) and σ*(2s).
• The remaining 4 electrons occupy the π(2p) orbitals (2 electrons in each π orbital, degenerate in energy).

Notice:

• The σ(2p) and all antibonding π* and σ* orbitals are empty.
• This gives bond order = (bonding electrons – antibonding electrons)/2 = (8 – 4)/2 = 2

Thus, C₂ has a double bond and is diamagnetic (all electrons are paired). Interestingly, this contrasts with Lewis structures which suggest a single or triple bond. MO theory provides a more nuanced view, showing that the bonding involves primarily p-orbitals in π interactions.

This diagram and analysis explain the electronic structure and bonding nature of C₂.