Resonance

The benzene molecule consists of a hexagonal ring which is very stable despite its alternating single and double bonds. Pauling showed that if all atoms of a molecule were in a single plane and symmetrically placed, as in the benzene ring, the bonds are neither single nor double, but something in between. This concept of resonance made chemical reactions more predictable and increased molecular stability.
 Linus Carl Pauling United States 1931 Resonance

The benzene molecule consists of a hexagonal ring which is very stable despite its alternating single and double bonds. Pauling showed that if all atoms of a molecule were in a single plane and symmetrically placed, as in the benzene ring, the bonds are neither single nor double, but something in between. This concept of resonance made chemical reactions more predictable and increased molecular stability.