What concept describes bonding that cannot be correctly represented by a single Lewis structure?

• A. Resonance
• B. Lewis Structure
• C. Structural Formula
• D. Polyatomic Ion

Answer: (A)

Resonance describes bonding that cannot be correctly represented by a single Lewis structure because electrons can be delocalized over several atoms. In these cases there are multiple valid Lewis structures, called resonance forms, that differ in where bonds and lone pairs are placed. The real molecule is a resonance hybrid, with bond characteristics—like bond order and lengths—that are intermediate between the options shown in any one form. A classic example is benzene, where the electrons are spread around the ring so all carbon–carbon bonds are equivalent, something a single Lewis structure can’t capture. Another example is the nitrate ion, which can be drawn with the double bond to one oxygen or another configuration with the double bond in a different place; the actual structure is a blend with partial double-bond character in all N–O bonds. The other terms—Lewis structure as a single representation, structural formula as connectivity, and polyatomic ion as a charged group of atoms—don’t describe this delocalization phenomenon.