perchromate ion vs chromate ion

[arpitpatel86]

some1 please explain to me why perchromate is CrO and chromate is CrO4

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[doc3232]

some1 please explain to me why perchromate is CrO and chromate is CrO4

There are a LOT of chromate ions and they always just fully oxidize.
K2Cr2O7 H2CrO4 CrO3
These are the only 3 that I have seen, but they all do the same things.
I would assume CrO3 would do the same.

and I just re-read your question......
Generally the "middle" molecule has no prefixes.
As for the "per," think of perchlorate and chlorate, ClO3 for chlorate and perchlorate for the less oxidized form, ClO.