Representation of a Molecular Structure as a Resonance Hybrid

When a reasonable (octet rule is satisfied) Lewis representation has a minimum of formal charges, it is usually a suitable description of the structure of the species (molecule or ion).

If two or more equivalent Lewis structures can be drawn, the species is best represented as an average, or combination, or resonance hybrid of all the equivalent structures. Examples of this include the benzene molecule, the ozone molecule, the acetate anion, the carbonate anion and the nitrate anion. In this way the equivalence of atoms within the species, or symmetry, is included in the representation of structure.