Oxidation Number

The oxidation number of oxygen in most of the compounds is -2 except in peroxides(-1), superoxides (-1/2), oxygendifluoride (+ 2).

In (chromium pentoxide), the chromium atom is surrounded by peroxide groups ( ). To find the oxidation state of Cr, we consider the following: - The peroxide group ( ) has an overall charge of -2. - There are 5 peroxide groups, so their total charge is -10. - To balance the charge, chromium must have an oxidation state of +6. Thus, the oxidation number of Cr in is +6.