When does oxygen count?

[Sandra U 2E]

Hi, I’m a little confused on how the oxygens in an oxelate ion (bidentate) or CO₃^2- (mono/bidentate) are not considered when determining what kind of ligand they are but, at least to my understanding, most of the oxygens in EDTA are considered, making it hexadentate. What is the difference that makes the oxygens in EDTA count but not for the others? Is there a pattern to be aware of? If the oxygens were, say, sulfurs, would this pattern still remain the same? Thanks!

[Danis Rivera 2C]

In EDTA, all the oxygens are involved in bonding with the metal, while in oxalate and carbonate, some of the oxygens are used because of different shapes.