Ion Peroxide has 1- or 2- charge???

I believe oxidation # of Oxygen in compounds is -2 except when in Peroxides. In which case, it has -1. That's how I learned thru my proffessor.
BUT it's O2 2- according to my text.(Peroxide is in 2- group in the text). I'm quite confused. I have an exam tomorrow and there is no way of asking my proffessor, so please help me.

EX) Calculate the oxidation # of X in the following
2X + 2(-1) = 0
2X - 2 = 0
2X = 2

X + 2(-2)=0
X - 4 = 0
X = 4

The answers are correct, NO???
Then what am I missing???
Please help me.
Thank you so much.


Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Your answers, I believe, are correct, assuming the first example is a peroxide (two oxygens joined together, with overall charge 2-) and the second example is just a commonal garden oxide (two oxygens bonded to X, not bonded to each other, each having a charge of 2-)

The peroxide ion has an overall charge of -2
But when things bond to it, they usually (always?) bond with one thing bonded to one oxygen, and the other to the other oxygen. Each oxygen carried a -1 charge.

It's better to look at the binding using dot a cross, so you can understand the layout of the electrons better.

So the peroxide ion is 2-, but each bond to each oxygen is -1, if that makes sense.

WebElements: the periodic table on the WWW []

Copyright 1993-20010 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.