Energy Levels for Antibonding Molecular Orbitals

[Albert Chong_1L]

Hi,

For antibonding molecular orbitals, I was wondering why the sigma*s orbitals have a higher energy than the pi*p orbitals. In bonding orbitals, the opposite is true because s orbital electrons penetrate less than p orbital electrons.

Thanks.

[Chem_Mod]

Imagine you have two waves that interfere constructively very strongly. You take one of the waves and shift it half-wavelength, then now your two waves will interfere destructively very strongly. So the more stable the bonding orbital, the more unstable its corresponding antibonding orbital.