Final answer:
The Lewis structure for carbonate shows one double bond and two single bonds with oxygen atoms, but due to resonance, all three C-O bonds are actually equivalent. This equivalence results in three resonance forms for the carbonate ion, and the true structure is a hybrid average of these forms.
Step-by-step explanation:
The Lewis structure for the carbonate ion (CO₃²⁻) involves placing the carbon atom in the center with three oxygen atoms surrounding it. Each oxygen has six valence electrons and carbon has four, which are shared to form a stable structure with octets around each atom. This structure is represented by one oxygen having a double bond with carbon and two others having single bonds, while also having two extra electrons to account for the -2 charge. However, because all three oxygen atoms are equivalent, the double bond can be located at any of the three oxygen positions, leading to three different resonance forms. These resonance forms show the same arrangement, just with the double bond's position varying among the oxygen atoms. Experiments have shown that all C-O bonds in CO₃²⁻ are of the same length, implicating that the actual distribution of electrons is a hybrid of all three resonance forms, where each C-O bond is a blend and has a bond-order of 1.33.