Class 11 Chemistry Chemical Bonding Structure Resonance


It is given by Heisenberg.

He took a molecule of ozone. Its structure was represented as:


According to the structure, it is clearly seen that it has one double bond and another single bond. So, obviously the bond lengths will be different. For double bond between oxygen atoms, the bond length is 121pm and for single bond it is 148pm.

But, the bond length was found experimentally to be same for both the bonds that is 128pm .This bond length lies in between the values of single and double bond lengths.


So, this proved that this structure is not able to explain and prove all properties .So ,it was assumed that ozone has two structures:



  • The pi electrons can be delocalized ,therefore they make weak bond.The resonating structures are hypothetical structures drawn just to explain their properties.
  • We know less energy, more stability .So, out of this canonical structure the one which will have low energy will contribute more towards actual structure.

Resonance structures: Is defined as difference  between actual bond energy and energy of most stable resonating structures.



  • Resonance averages the bond characteristics of a molecule as a whole.
  • Resonance stabilizes the molecule because energy of the resonance hybrid is less than the energy of any canonical forms.


  1. It has no real existence.
  2. Resonance has same bond length.
  3. Resonance hybrid has lowest energy.
  4. Greater the resonance and resonance energy the more stable is the structure.
  5. Resonance is theoretical concept with no experimental verification.

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