Resonance recognizes that there can be alternative ways to couple electrons that are energetically equivalent. Benzene is one of the archetypical examples of resonance. Here are coupling diagrams for the two forms:

Benzene does not have alternating single and double bonds. It has D_6h symmetry. There are six equivalent σ bonds and six electrons in out-of-plane π bonds that are shared equally among the six carbon atoms. Glyph-based coupling diagrams handle resonance straightforwardly.

In the next section, we will consider ionic and dative bonding.