[saman_Z]

for instance oxide is (O)2- while peroxide is (O-O)2-
Similarly manganate is (MnO4)2- and permanganate is(MnO4)- . Why are they named so??

[Dungsbars]

Per means higher oxidation state. MnO₄^2- has Mn at +VI, while MnO₄^- has Mn at +VII. O^2- has O at -II, while O₂^2- has O at -I.

[ARGOS++]

Dear Saman_Z;

You can find a lot about this Nomenclature, if you search on the Internet for:   

“prefix per peroxide permanganate”

Good Luck!
                    ARGOS⁺⁺

[macman104]

Using ARGOS's search, it appears that originally it was used for acids that were formed from Hydrogen Peroxide or release it upon treatment with sulfuric acid.  You read the first few pages of this book:

http://books.google.com/books?id=kxFDAAAAIAAJ&printsec=titlepage

But I suppose what you are really asking is why do we use the prefix "per" and not..."foo" or whatever you want.  That may or may not be online, or it may be one of those relics that no one knows why it's called per, not sure.

[ARGOS++]

Dear macman104;

For “per-” see on:    http://www.affixes.org/p/per-.html
                     or :   http://www.merriam-webster.com/dictionary/per-

Good Luck!
                    ARGOS⁺⁺

[macman104]

Thanks, that's what I was looking for.

Actually, that first link looks exactly like what you want.

[saman_Z]

thankyou so much, ARGOS++  and MACMAN 104!!!!! ..

[ARGOS++]

Dear Saman_Z;

You’re welcome!   ─   Soon again.

Good Luck!
                    ARGOS⁺⁺