Answer
The application of molecular orbital theory to the heteronuclear diatomic molecule HF involves the combination of the 1s orbital of hydrogen and the 2s and 2p orbitals of fluorine to form bonding and antibonding molecular orbitals. The resulting electronic configuration and bond order explain the stability and covalent nature of the HF molecule.
Work Step by Step
To describe the bonding in the heteronuclear diatomic molecule HF (hydrogen fluoride) using molecular orbital (MO) theory, we need to consider the following steps:
1. Determine the atomic orbitals involved:
- Hydrogen (H) has one 1s atomic orbital.
- Fluorine (F) has five atomic orbitals: one 1s, three 2p, and one 2s.
2. Construct the molecular orbitals:
- The 1s orbital of hydrogen and the 2s and 2p orbitals of fluorine will interact to form the molecular orbitals.
- The 1s orbital of hydrogen will combine with the 2s and 2p orbitals of fluorine to form bonding and antibonding molecular orbitals.
3. Determine the energy levels of the molecular orbitals:
- The bonding molecular orbitals will have lower energy levels than the individual atomic orbitals, while the antibonding molecular orbitals will have higher energy levels.
- The order of the energy levels from lowest to highest is: σ1s (bonding), σ*1s (antibonding), π2p (bonding), π*2p (antibonding).
4. Populate the molecular orbitals:
- Following the Pauli exclusion principle and Hund's rule, the electrons will occupy the molecular orbitals in the order of increasing energy.
- In the case of HF, the electronic configuration is: (σ1s)2 (σ*1s)0 (π2p)4 (π*2p)0.
5. Determine the bond order:
- The bond order is calculated as (number of bonding electrons - number of antibonding electrons) / 2.
- For HF, the bond order is (2 - 0) / 2 = 1, indicating a single covalent bond.
6. Explain the stability of the molecule:
- The bonding in HF is stabilized by the formation of the σ1s bonding molecular orbital, which has a lower energy than the individual atomic orbitals.
- The antibonding σ*1s orbital remains unoccupied, further contributing to the stability of the molecule.
