What is Resonance Theory?

The resonance structures are defined as a group of two or more Lewis structures that can collectively represent a single polyatomic species. This will display the electronic bonding that exist between the metals and that will include the fractional bonds and the fractional charges.

This can be described as the combination of several contributing structures that forms that leads to the formation of hybrid resonance structures in accordance with the valence bond theory that is with association of certain molecules and ions.

In most cases, a single Lewis structure fails to explain the bonding in a molecule due to the presence of partial charges as well as fractional bonds in it. In these circumstances, the resonance structures will lead to the chemical bonding.

The bonding in case of the molecules or ions happens by merging many contributory structures or forms.  There is a resonance structure is described below:


In the process of delocalization of electrons that can be explained as the fractional bonds. How stable the structure will be will depend on the type of bond that they will exhibit. This is known as the Resonance Hybrid. In this case the resonance structures are not equivalent.

It will also be important to determine which one(s) best describe the actual bonding. In this the formal charge of the electron bonding can be used to predict the most favorable resonance structure.


There are four types of resonance that are based on the orbital the electrons that are placed in and also on the base of the electron bond that exists. 

Type 1: This resonance is said to be the interaction of an empty p-orbital and an adjacent electron pair.  This is circulating in terms of the simple π-bond. This type of resonance structure will result in a structure analogous to a simple π-bond.

Type 2:  In this phase there is interaction between the empty orbital and a π-bond. The most important examples for that are allelic and benzyl systems.

Type 3: In this type of structure, the electron pair and an adjacent π-bond will produce allelic or benzyl anions.  In field of organic chemistry, the focus is not more on the ionic bonds.  A look into the reaction levels of the elements and also the reason why they are termed to be so very important.

Type 4 in resonance there is one where we have two (or more) π-bonds interacting with each other. In this mixture of the bonds that we take into consideration is strictly speaking, conjugated, for the multiple π-bonds participating in resonance as a “conjugated system” due to their special chemical properties.


In this the bond lengths of both nitrogen-oxygen bonds are equal. The Lewis dots structures tend to represent the different types of the bonds in which there will be a combination of nitrogen and oxygen bonds.

We are here to know the formation of these structures so that we will be able to have a clear understanding of the resonance structure as well. The resonance hybrid of this polyatomic ion, obtained from its different resonance structures, can be used in explaining the equal bond lengths.

  The reaction process below will explain the elaborate structures as well:

Resonance Structures of NO2

Resonance Structures of NO2- Ion

According to the resonance hybrid of NO2– each oxygen atom holds a partial charge of magnitude -½. Here the bond length of the N-O bonds is found to be 125 pm. This will help us to place the resonance structure of nitrogen.


This process will explain the ozone gas formation. In this the ozone molecule consists of a central oxygen atom. It is singly bonded to one oxygen atom and doubly bonded to another. 

There is no one charge that the Lewis structures of this molecule show a +1 charge on the central oxygen and a -1 charge on the singly bonded oxygen. These two are the places where the resonance structures are to be accumulated and the figure below explains the same.

Resonance Structures of O3

Resonance Structures of O3

In this kind of structure the resonance hybrid of the ozone gas here has a +1 charge associated with the oxygen which is at the centre and a partial charge of – (½) associated with the other oxygen atoms.

There will be definite composition of the structures as well. The resonance theory will be helping us understand the structure formation of the atoms. There will be a structural representation for the same.