To understand the bonding in lithium hydride (LiH), we can analyze the molecular orbitals (MOs) formed by the overlap of atomic orbitals from lithium (Li) and hydrogen (H).
In LiH, lithium has an electron configuration of 1s22s1 and hydrogen has an electron configuration of 1s1. When these two atoms come together to form LiH, the 2s orbital of lithium interacts with the 1s orbital of hydrogen.
The molecular orbital diagram for LiH can be constructed as follows:
- The 1s orbital of hydrogen is lower in energy compared to the 2s orbital of lithium, due to the difference in electronegativity and atomic size.
- When these orbitals combine, they form two molecular orbitals: a bonding molecular orbital (σ1s) and an antibonding molecular orbital (σ1s*)
The bonding molecular orbital (σ1s) is lower in energy and is filled with the two electrons from LiH – one from lithium’s 2s orbital and one from hydrogen’s 1s orbital. The antibonding molecular orbital (σ1s*) is higher in energy and remains unoccupied.
The energy splitting can be visualized as follows:
Energy
+-------------+
| σ1s* |
+-------------+
| σ1s |
+-------------+
Since the bonding molecular orbital is occupied, it leads to a net stabilization of the system, which indicates that the formation of LiH is indeed favorable. The total energy of the system decreases when the bond is formed, leading to a more stable arrangement.
In summary, the energy splitting diagram confirms that the bonding in lithium hydride is favorable due to the population of the bonding molecular orbital, resulting in a stable diatomic molecule.