Which of the following correctly represents the molecular orbital (MO) energy diagram for Li\(_2^+\), considering only the 1s and 2s atomic orbitals?

• A. Both 1s and 2s atomic orbitals combine to form only antibonding MOs.
• B. The 2s atomic orbitals combine to form a single nonbonding MO, and the 1s atomic orbitals remain unchanged.
• C. The 1s atomic orbitals combine to form only a bonding MO, while the 2s atomic orbitals do not participate in MO formation.
• D. The 1s atomic orbitals combine to form a lower-energy \(ext{σ}_{1s}\) bonding MO and a higher-energy \(ext{σ}^*_{1s}\) antibonding MO; the 2s atomic orbitals combine to form a lower-energy \(ext{σ}_{2s}\) bonding MO and a higher-energy \(ext{σ}^*_{2s}\) antibonding MO.

Answer: (D)

Verified step by step guidance

1. Recall that molecular orbitals (MOs) are formed by the linear combination of atomic orbitals (AOs) from the bonded atoms. For diatomic molecules like Li\(_2^+\), the 1s and 2s orbitals from each lithium atom combine to form bonding and antibonding MOs.
2. Understand that each pair of atomic orbitals (1s with 1s, and 2s with 2s) combines to form two molecular orbitals: one bonding MO (lower energy) and one antibonding MO (higher energy). This is a fundamental principle of MO theory.
3. For the 1s orbitals, the combination results in a bonding molecular orbital labeled \(\text{σ}_{1s}\) and an antibonding molecular orbital labeled \(\text{σ}^*_{1s}\). The bonding MO is lower in energy than the original atomic orbitals, while the antibonding MO is higher in energy.
4. Similarly, the 2s orbitals combine to form a bonding molecular orbital \(\text{σ}_{2s}\) and an antibonding molecular orbital \(\text{σ}^*_{2s}\). These orbitals are higher in energy than the 1s MOs but follow the same bonding-antibonding pattern.
5. Therefore, the correct MO energy diagram for Li\(_2^+\) includes both the 1s and 2s atomic orbitals combining to form bonding and antibonding molecular orbitals, specifically \(\text{σ}_{1s}\), \(\text{σ}^*_{1s}\), \(\text{σ}_{2s}\), and \(\text{σ}^*_{2s}\).