[michaelscwu]

As a general rule, when a polyatomic ion's prefix or suffix changes it just means that the ion either has more or less oxygen but retains the charge.
i.e. carbonATE CO3 (2-) and carbonITE CO2 (2-)

How come manganate, MnO4 (2-), has the same number of oxygen as PERmanganate, MnO4 (1-), and has a different charge?

Shouldn't PERmanganate have 1 more oxygen than manganate, and shouldn't the two have the same charges?

[Borek]

Shouldn't PERmanganate have 1 more oxygen than manganate, and shouldn't the two have the same charges?

Well, mother nature doesn't follow our general rules, quite the opposite - our general rules try to follow mother nature. The don't always succeed.

[michaelscwu]

Shouldn't PERmanganate have 1 more oxygen than manganate, and shouldn't the two have the same charges?

Well, mother nature doesn't follow our general rules, quite the opposite - our general rules try to follow mother nature. The don't always succeed.

Is there a reason why though? Are they two completely different things?

[Borek]

Not sure what you are asking about this time.

Manganate and permanganate are two different things. They differ by one electron.

Cr²⁺ and Cr³⁺ are two different things. They differ by one electron.

Fe(CN)₆^3- and Fe(CN)₆^4- are two different things. They differ by one electron.

[lancenti]

I think that the prefix of PER such as that found in Perchlorate and Permanganate simply mean that it's one oxidation state higher and not that there should be one more oxygen atom attached.

EDIT:

I think that the reason we have this idea comes from how PERoxide = 2 oxygen atoms.