Molecules with a combination of multiple and single bonds may exist in resonance structures. In the carbonate ion , for example, the carbon forms one double bond and two single bonds with the oxygens. However, there are three possible structures for this molecule.
The molecule actually exists in a hybrid structure that is a combination of the three structures given in (1). This structure is represented either by placing double-headed arrows between the structures in (1) or by using a dotted line instead of marking the double bonds.
