Final answer:
Resonance occurs when multiple valid Lewis structures can depict a molecule or ion, suggesting that the electrons are delocalized. The concept of a resonance hybrid better represents the actual bonding situation, as seen with carbonate ions and benzene, by considering all bonds as having intermediate character rather than as separate single and double bonds.
Step-by-step explanation:
The concept of resonance in chemistry refers to situations where more than one valid Lewis structure can be drawn for a molecule or ion, indicating that electrons are delocalized across multiple atoms. For example, in the case of the carbonate ion (CO32-), there are three equivalent resonance forms. The oxygen atoms and the carbon are connected in such a way that each carbon-oxygen bond has an intermediate character, with a bond order of 1.33, rather than separate single and double bonds. This is sometimes represented in a resonance hybrid structure which most accurately reflects the actual bonding situation within the molecule.
Resonance structures imply a certain amount of delocalization of electrons, as is also seen in benzene (C6H6), where instead of alternating single and double bonds, all the carbon-carbon bonds are equal and of intermediate length and bond order. It's also notable that resonance does not occur with atoms in sp3 hybridization unless they contain a lone pair that can be moved into a p-orbital upon rehybridization to sp2.
Furthermore, having multiple resonance forms can contribute to the stability of the compound. This is referred to as resonance stabilization, which is stronger when more equivalent contributors are present. Thus, substances like the carbonate ion with three equal contributors will experience greater resonance stabilization than molecules with fewer such contributors.