Question

Explain the structure of $C{O}_3^{2-}$ ion in terms of resonance.

Answer 1

Resonance structure of $C{O}_3^{2-}$
"Whenever a single Lewis structure cannot describe a molecule accurately, a number of structures with similar energy, positions of nuclei, bonding and non-bonding pairs of electrons are taken as the canonical structures of the hybrid which describes the molecule accurately".

Resonance structure of $C{O}_3^{2-}$

In case of $C{O}_3^{2-}$ a single Lewis structure based on the presence of two single bonds and one double bond between carbon and oxygen atom is inadequate to represent the molecule accurately as it represents unequal bonds.

Experimental data reveals that all carbon to oxygen bond in $C{O}_3^{2-}$ are equivalent. Therefore, the carbonate ion is best described as resonance hybrid of the canonical forms $I,II$ and $III$ are shown below.