It has been observed experimentally that the carbon and oxygen bonds in CO₃^2- are equivalent. As we know that Lewis structure represents only unequal bonds. Hence, it is not enough to represent the molecule by Lewis structure accurately as it represents unequal bonds.

Hence it can be best explained by making its canonical structures and its resonance hybrid.

The structure I, II and III represent the three canonical forms (resonating structures) of CO₃^2-

The structure IV represents the structure of CO₃^2-more accurately. This is called resonance hybrid.