Resonance structures

[906155996]

Hello! I am confused on how the atoms move on the resonance structure and how, do we know where to start counting, when given a resonance structure?

[Annabelle Jeon 3K]

The atoms don't move on the resonance structure per se. We use the dotted lines to represented delocalized regions of electron density. I'm not entirely sure what you mean by when to start counting. But resonance structures are the possible variations of a molecule. The overall charge should be the same but we can still arrange it in a different way so there are different number of bonds, which creates charges in different parts of the molecule, but again, it should even out to the same overall charge of the molecule.

[105717435]

In a resonance structure atoms do not move only the electrons move meaning that the electron density fluctuate between the two atoms that are "happy" to take on additional electrons therefore delocalizing electron density because it is bounced between atoms.

[105561735]

When it comes to figuring out which resonance structure is best suit, try and find a structure whose formal charge is closest to 0 or if there is a question that gives you a molecule with a particular charge, try and ensure that the molecules add up to that charge