Resonance Structures
Some molecules are best described by several Lewis structures at once.
About this topic
Some molecules cannot be properly shown by a single Lewis structure. Ozone (O₃) and the carbonate ion (CO₃²⁻) have equivalent structures that differ only in where double bonds are drawn. The real molecule is a resonance hybrid, an average of the structures, with bond lengths and strengths in between single and double.
Resonance happens when electrons are delocalised across several atoms. In ozone, the two O–O bonds are identical in length (about 128 pm), between a single (148) and double (121) bond. The molecule does not flip between forms; each structure is just a limitation of our drawing method. Delocalisation makes molecules more stable, and the extra stability is called resonance energy. A double-headed arrow joins the contributing structures.
In carbonate, the double bond could be drawn to any of the three oxygens, giving three structures, and the real ion has three equal C–O bonds with a bond order of 1.33. Benzene, C6H6, has two Kekule structures and a hybrid with six identical bonds, explaining its unusual stability. Resonance also affects acidity and colour in dyes.
A common misconception is that the structures are rapidly interconverting isomers; they are not. The hybrid is a single, real structure, like a mule being a blend of horse and donkey rather than switching between the two.
Key ideas
- Ozone and benzene
- Electrons delocalised
- The real structure is a hybrid
Quick check
Use cases: where Resonance Structures helps
- Homework: review the key idea behind Resonance Structures before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Resonance Structures without notes.
- Visual learning: play with the interactive lab to see how Resonance Structures changes when you adjust its inputs.
- Teaching a friend: explain Resonance Structures in your own words, then compare your version with the key ideas.
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Frequently asked questions
What is Resonance Structures?
Some molecules are best described by several Lewis structures at once.
What will I learn in Resonance Structures?
Ozone and benzene. Electrons delocalised. The real structure is a hybrid.
Is Resonance Structures part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Resonance Structures lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Resonance Structures?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.