Can 1s and 2s atomic orbitals from molecular orbitals

Answer

To determine whether 1s and 2s atomic orbitals can form molecular orbitals, we need to consider the following steps:

### Step-by-Step Solution:

1. **Understanding Atomic Orbitals**:
- Atomic orbitals are regions in an atom where there is a high probability of finding electrons. The 1s orbital is the lowest energy orbital, while the 2s orbital is higher in energy.

2. **Energy Levels of Orbitals**:
- The 1s orbital is filled first as it has a lower energy level compared to the 2s orbital. The energy difference between these two orbitals is significant.

3. **Molecular Orbital Theory**:
- According to molecular orbital theory, atomic orbitals combine to form molecular orbitals. For effective overlap and bonding, the combining orbitals should have similar energy levels.

4. **Combining Orbitals**:
- In order to form molecular orbitals, orbitals must have comparable energies. Since the 1s and 2s orbitals have a substantial energy difference, they cannot effectively combine.

5. **Allowed Combinations**:
- The 1s orbitals can combine with other 1s orbitals to form molecular orbitals such as σ (sigma) and σ* (sigma star).
- Similarly, 2s orbitals can combine with other 2s orbitals to form their own molecular orbitals (σ and σ*).

6. **Conclusion**:
- Therefore, due to the significant energy difference between the 1s and 2s atomic orbitals, they cannot combine to form molecular orbitals.

### Final Answer:
No, 1s and 2s atomic orbitals cannot form molecular orbitals due to their significant energy difference.

---