Number of resonating structures (hypothetical)

To my knowledge, resonance happens where more than one lewis stucture can represent the compound with no shift in sigma bonds


so, suppose in a simple conjugated system even like 1-3 pentadiene , two forms are well known, i want to know if a third form where each atom has completely filled or completely empty p orbitals should also be taken into consideration, as technically, there is nothing wrong with it, I accept that it's "contribution" will be negligible, but it should be counted in all POSSIBLE resonating structures


<https://commons.wikimedia.org/wiki/File:Naphthalene_resonance_structure.svg> 


similar argument here, a lot more can be created if we allow charge separation of pi bond


EDIT: The question is whether there is a convention of some sort which tells us which ones to count which ones not (if we cant tell the magnitude of difference in stability of the structure)




Resonances structures are a model of the quantum mechanical orbital mixing. To my mind they are a complete farce. They are also quite useful


A model is a simplification of a problem, usually based on ignoring negligible factors. So this question really distills down to what is negligible and what isn't? 


That depends on roughly two factors:


1. The conditions of reaction.


Are the conditions strongly ionic or acidic? Then charge separation may become relevant.


2. The rigor of the problem.


Is this for a high school course? A Ph.D. thesis? A bar-room chat with your mates?


Unfortunately, like most of chemistry, there is not an absolute answer here.


 2