Here’s a explanation of how Molecular Orbital (MO) Theory explains resonance:
1. What is Resonance?
- In some molecules, a single Lewis structure cannot describe the bonding fully.
- Electrons are delocalized (spread out) over two or more atoms instead of being fixed in one bond.
- Example: Benzene (C₆H₆) — the double bonds keep shifting positions.
2. MO Theory and Resonance
- MO theory says that atomic orbitals combine to form molecular orbitals that belong to the whole molecule.
- Electrons in these molecular orbitals are delocalized over several atoms, not confined to a single bond.
- This delocalization is exactly what resonance describes in Lewis structures.
3. Example: Benzene
- In benzene:
- Each carbon atom has a p orbital.
- These six p orbitals combine to form six π molecular orbitals that extend over all six carbons.
- The π electrons are shared equally across all carbon atoms, not fixed between individual pairs.
- So, the molecule is stabilized due to delocalization — this is the resonance stabilization.
4. Key Point
- Resonance structures in Lewis theory are just a way to show electron delocalization, but MO theory gives a real picture: the electrons are truly spread over the whole molecule.