Representation of Antibonding Sigma (σ*) Molecular Orbital

Question:
When ψ_A and ψ_B are the wave functions of atomic orbitals, then antibonding sigma (σ*) molecular orbital is represented by:

Correct Answer: ψ_A − ψ_B

Explanation (Molecular Orbital Theory)

According to Molecular Orbital Theory, atomic orbitals combine either by addition or subtraction of their wave functions.

Bonding molecular orbital (σ):
Formed by constructive interference:

σ = ψ_A + ψ_B

This increases electron density between the nuclei and stabilizes the molecule.

Antibonding molecular orbital (σ*):
Formed by destructive interference:

σ* = ψ_A − ψ_B

This creates a node between the nuclei, decreases electron density and destabilizes the molecule.

Hence, the correct mathematical representation of antibonding sigma molecular orbital is:

ψ_A − ψ_B

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