I've always thought that the two-form resonance structure of ozone was the scientific concensus (from Wikipedia]:

Two-form resonance structure of ozone

Then today I found two other opinions. A three-form structure:

Three-form resonance structure of ozone

And a four-form structure:

Four-form resonance structure of ozone

Is there a consenus? Are the two and three-form representations just simplifications of the four-form structure? Please include references.

EDIT: The second resonance structure on the four-form image above is drawn incorrectly, as pointed out by @ron. The upper oxygen atom should have a lone pair and a positive charge, just like the second structure of the two-form.


2 Answers 2


Those are all valid resonance structures for ozone (except the second from the left in the "four-form structure" row, that one has two negative charges, maybe it's a typo). In fact you can draw even more structures like this one, where this is no single bond between the middle and terminal-right oxygens.

enter image description here

All of these structures contribute to the "real" structure of ozone - however, some resonance structures contribute more and some resonance structures contribute less. Here is a link to a nice set of rules (see page 2, the "Resonance Contributor Preference Rule" section) that describes how to weight the contribution of various resonance structures. The most important rule is that each atom in the resonance structure should have an octet of electrons. Only the structures labeled I and II in your "three-form structure" row meet this requirement, so they are the two most important resonance structures for ozone - but all of the others do contribute, just to a lesser extent.


Covalent bonds suppose to help an atom achieve filled valence shell by sharing electrons. Resonance structures need to have maximum atoms adhering to the octet rule. Look at III, the oxygen atoms on the right and left have only 7 electrons in their valence shall even AFTER forming covalent bonds. That is why it is not one of the resonance structures.


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