There are many well-known differences in the physical and chemical properties of ozone (O-3) and sulfur dioxide (SO2). O-3 has longer and weaker bonds than O-2, whereas SO2 has shorter and stronger bonds than SO. The O-O-2 bond is dramatically weaker than the O-SO bond, and the singlet triplet gap in SO2 is more than double that in O-3. In addition, O-3 is a very reactive species, while SO2 is far less so. These disparities have been attributed to variations in the amount of diradical character in the two molecules. In this work, we use generalized valence bond (GVB) theory to characterize the electronic structure of ozone and sulfur dioxide, showing O-3 does indeed possess significant diradical character, whereas SO2 is effectively a closed shell molecule. The GVB results provide critical insights into the genesis of the observed difference in these two isoelectronic species. SO2 possesses a recoupled pair bond dyad in the a ''(pi) system, resulting in SO double bonds. The pi system of O-3, on the other hand, has a lone pair on the central oxygen atom plus a pair of electrons in orbitals on the terminal oxygen atoms that give rise to a relatively weak pi interaction.