Resonance in Lewis Structures


For some molecules, there are two or more equally valid Lewis structures. Some examples are below.



When there are two equivalent Lewis structures, the bonding of the molecule is likely to be an average of the two.

Think about the molecular orbital diagram of each of these molecules. After forming sigma bonding and sigma antibonding orbitals, three contiguous atoms have a remaining p orbital. These p orbitals are pointing in the same direction, let's call that the x direction.

The Lewis structures show a double bond between either the first 2 atoms or the second 2 atoms. The two structures differ only in the pi bonding.

Can we illustrate pi bonding that extends over 3 or more atoms in a molecular orbital diagram?

First, consider the hybridization of the oxygen atoms in ozone.



After forming the sigma bonds with the 2sp2 hybrid orbitals between the atoms, each oxygen atom has a remaining 2p orbital for pi bonding.


Professor Patricia Shapley, University of Illinois, 2012