Show how a hydrogen 1s atomic orbital and a fluorine 2p atomic orbital overlap to form bonding and antibonding molecular orbitals in the hydrogen fluoride. Are these molecules sigma or pi molecular orbitals?
To understand how a hydrogen 1s atomic orbital and a fluorine 2p atomic orbital overlap to form bonding and antibonding molecular orbitals in hydrogen fluoride (HF), we need to consider the molecular orbital theory.
1. Draw the atomic orbitals:
Start by drawing the hydrogen 1s orbital and the fluorine 2p orbitals. The hydrogen 1s orbital is spherically shaped, while the fluorine 2p orbitals are dumbbell-shaped with three equivalent p orbitals (2px, 2py, and 2pz).
2. Determine the overlap type:
The overlap between the hydrogen 1s orbital and the fluorine 2p orbitals will result in the formation of two molecular orbitals: a bonding molecular orbital (σ) and an antibonding molecular orbital (σ*).
3. Determine the molecular orbital symmetry:
In this case, the bonding molecular orbital (σ) forms by the head-to-head overlap of the hydrogen 1s orbital and the fluorine 2p z orbital. This molecular orbital is symmetrical around the internuclear axis, and thus it is a sigma (σ) molecular orbital. The bonding orbital is lower in energy than the starting atomic orbitals, indicating a stable bond formation.
4. Determine the antibonding molecular orbital:
The antibonding molecular orbital (σ*) forms by the overlap of the hydrogen 1s orbital and the fluorine 2p z orbital with opposite phase or wave function. This molecular orbital has a nodal plane perpendicular to the internuclear axis, dividing the electron density into two lobes. Since it is symmetrical about the internuclear axis, it is also a sigma (σ) molecular orbital. The antibonding orbital is higher in energy than the starting atomic orbitals, indicating destabilization and a weak interaction.
Therefore, the molecular orbitals formed by the hydrogen 1s and fluorine 2p overlap are sigma (σ) molecular orbitals.