Final answer:
The identical C—O bond lengths in the carbonate ion validate the resonance theory, where the electrons are delocalized over the entire molecule, producing an averaged bond order that results in all bonds being equivalently between a single and double bond.
Step-by-step explanation:
The carbonate polyatomic ion showcases identical bond lengths of 136 pm among all three C—O bonds, which is a significant piece of evidence supporting the concept of resonance. Typically, single and double bonds have different lengths due to the difference in their bond strengths. However, resonance theory suggests that instead of having fixed single and double bonds, the electrons are delocalized across the entire molecule, leading to an average bond order that is the same for all C—O bonds. Thus, each bond has a bond order of 1.33, indicating the sharing of bonding characteristics between single and double bonds and resulting in identical bond lengths. The presence of equivalent resonance structures also indicates that each oxygen has the potential to be the one with a double bond to carbon, but the true representation is a hybrid of all possible structures, where the bonding is an average of these resonance forms.