CHEM 121 glossary

Resonance

The situation where two or more valid Lewis structures differ only in where the electrons (lone pairs and multiple-bond pairs) sit, with the atoms in the same places. The forms are joined with $\leftrightarrow$ ; none of them alone is the real species.

One of the three equivalent resonance forms of carbonate; the C=O can sit on any O.

Example

The formate ion, $\ce{HCOO-}$ , has 2 resonance forms, so each C–O bond has bond order $\tfrac{2+1}{2} = 1.5$ and the two C–O bonds are the same length.