# How do you work out the oxidation number of an element in a compound? E.g finding the oxidation number of the element Cr from the compound Cr2O3

Jan 8, 2018

The overall compound has a no charge (neutral). That means the positive and negative charges are equal in number. For the compound $C {r}_{2} {O}_{3}$, Chromium is a metal and hence its oxidation number is positive, lets say +x is its oxidation number. The oxidation number of oxygen is already known i.e -2. So, we can write an equation, as

$2 \cdot \left(+ x\right) + 3 \cdot \left(- 2\right) = 0$
(We equate it to zero because he overall charge is 0)

or 2$x - 6 = 0$

or $2 x = + 6$

or $x = + 3$