Resonance Structures - Same Formal Charges or No?

[Joanna Zhao 1J]

Do the resonance structures for a molecule have to all have the same formal charges for each atom? I'm doing the Achieve textbook problems in 2C: Beyond the Octet Rule. For 2C.3a, the answer key says IO4- ion has four resonance structures with three I-O double bonds, a formal charge (FC) of 0 on the central iodine, FC of 0 on 3 O atoms, and FC of -1 on the fourth. The IO4- Lewis structure that obeys the octet rule (FC of +3 on central iodine) isn't grouped in. This follows my traditional understanding of resonance structures.

However, for 2C.3c, HClO3's stablest form with a FC of 0 on the Cl atom isn't the only structure. There are two more structures (totaling to three resonance structures), one with a FC of +1 on Cl and one with a FC of +2 on Cl. So, the resonance structures on HClO3 all have different formal charges, and they do not follow the lecture definition of having bonds in different equivalent locations.

Which begs the question, why are the resonance structures for HClO3 different in terms of bonds and formal charges? Can resonance structures be inequivalent after all? If HClO3 can have a resonance structure with a Cl atom with a FC of +2, why can't IO4- have a resonance structure with an I atom with a FC of +3? Or, am I misinterpreting the key?

[Chem_Mod]

Yes, resonance structures can have different formal charge distributions. Resonance hybrid essentially means that the actual existence is a blend of multiple resonance structures. More stable structures with minimal formal charges with contribute more, or are said to be major structures. While, less stable structures are minor and contribute less.

[Ashley Presnell 1C]

Resonance structures can have different formal charge distributions as bonds are not placed in the same places, affecting the formal charges of inidivual atoms in a molecule. Since the actual structure is an average of the resonance structures, it will be more heavily skewed to more stable structures with lower formal charges.

[Joanna Zhao 1J]

That makes sense. Thank you for clearing this up. Following this reasoning, is the IO4- ion with the +3 formal charge on central iodine just too unstable to exist and contribute to resonance?