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Some chemical molecules cannot be satisfactorily described by a single configuration of bonded atoms. The theory of resonance is concerned with the representation of such molecules by a dynamic combination of several structures, rather than by any one of them alone. The molecule is then conceived as 'resonating' among the several conceivable/describable structures and is said to be a 'resonance hybrid' of them. The classic example is the benzene molecule with 6 carbon atoms linked together in a ring. This is one of the basic features of many larger molecules essential to life. Its cyclic form only became credible when it was shown that the structure oscillated between two (and later five) extreme cyclic forms.
[Features]The precisely defined nature of the structural extremes in contrast with the lack of precision concerning the ordering of this oscillation between them.
[Contrast]The concept of resonance is not at present used as a metaphor except occasionally in referring to the relationship between two people (or groups) who are 'in resonance'.
[Keys]Typology of molecular resonant structures. Probabilistic nature of chemical resonance. Implication for complementary paradigms of any kind (e.g. wave versus particle explanation).