Delocalization happens when electric charge is spread over more than one atom. For example, bonding electrons may be distributed among several atoms that are bonded together.

How do you know when electrons are delocalized?

The easiest way to spot delocalized electrons is to compare electron locations in two resonance forms. If a pair appears in one place in one form, and in a different place in another form, the pair is delocalized.

What causes delocalization of electrons?

Since conjugation brings up electron delocalization, it follows that the more extensive the conjugated system, the more stable the molecule (i.e. the lower its potential energy). If there are positive or negative charges, they also spread out as a result of resonance.