What is the difference between a resonance structure and a resonance hybrid structure?
A Lewis resonance structure is one structural "snapshot" out of many that contribute to a molecule or polyatomic ion's overall, real-life resonance hybrid structure.
Let us take
The resonance hybrid structure is actually
because in reality, the electrons in this polyatomic ion are delocalized, meaning that they travel freely throughout the system.
Because the electrons aren't fully localized as one
The individual resonance structures simply illustrate still states for the electron distributions that contribute to the overall resonance hybrid.