Question

What is the resonance structure for `CO_3^-2`?

Answer 1

`CO_3^(2-)` `=` `(O=)C(-O^-)_2`

Explanation:

There are `4+6+6+6+2` valence electrons, i.e. 12 electron pairs to distribute over 4 centres. Of course, the resonance structure features 3 regions of electron density around a central carbon, and thus a trigonal planar structure. The oxygen atoms are all equivalent, and each `C-O` bond has partial double bond character.