Resonance of valency structures

Following a similar argument for the molecule of benzene, it is impossible to prefer one of the two valency forms to the other since the electron of the first carbon atom may equally well be exchanged with that of the second carbon atom as with that of the sixth. Consequently both forms exist in the molecule and when these are superimposed there arises the transitional structure which possesses a lower energy th n either of the original states and is therefore more stable. Unfortunately it is impossible to represent this transitional structure with the use of the conventional valency nomenclature and it was to overcome this difficulty that the idea of the resonance of valency structures was introduced by Slater and Pauling. The which-tly... 

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