According to the sources, a single Lewis structure for the carbonate ion ($CO_3^{2-}$), showing one double bond and two single bonds, is inadequate because experimental data proves that all three carbon-to-oxygen bonds are equivalent . This equivalence is explained by resonance, where the ion is a hybrid of three canonical forms . Consequently, all three bonds have the same length, which is intermediate between a single and a double bond, resulting in a bond order between 1 and 2 (specifically 1.33) . Furthermore, the central carbon atom in the carbonate ion is $sp^2$ hybridised to maintain its trigonal planar geometry, not $sp^3$ . The structure contains three sigma ($\sigma$) bonds and one delocalised \pi ($\pi$) bond, rather than three separate $\pi$-bonds .