How to determine substance oxidation level

How to determine substance oxidation level

Oxidation level – the conditional charge of atom in connection calculated proceeding from the assumption that it consists only of ions. Some elements have constant oxidation level, others are capable to change it. That to determine it at the substances having in different connections, various values we will use a special algorithm.


1. oxidations it is written degree over designation of an element, stitched together the sign, and then value is put. It can be negative, positive or equal to zero. The sum of all oxidation levels is equal in substance to zero. Some substances have constant oxidation levels in all connections. For example, at metals it always is positive and is equal to their valency (abilities to attach or replace a certain number of atoms or groups of atoms). Alkaline metals have the oxidation level +1, and alkaline-earth - +2. Hydrogen always has the oxidation level +1, an exception are hydrides, there--1 (for example, KH(-1)). Oxidation level of oxygen is equal-2, exceptions: peroxides (BaO2(-1)) and fluoride of oxygen (O (+2)F). Fluorine always has-1 (NaF(-1)).

2. If substance consists of one or several atoms of the same name, i.e. is simple, then extent of its oxidation is equal to zero. For example, H2, Ag, O2, Na, etc.

3. In complex substance first of all we place values of oxidation levels at elements at which it does not change. Then we work out the equation from one unknown, i.e. we designate the oxidation level which needs to be found for X. We solve this equation, we receive required size. It should be noted that in the presence in complex substance several atoms of the same element extent of its oxidation by drawing up the equation is multiplied by quantity of elements. Let's consider on examples.

4. If necessary to find sulfur oxidation level in substance Na2SO4 we act this way: at first we place values known to us: Na(+1)2SO(-2)4. We designate sulfur oxidation level for X, we write down the equation, remembering that the sum of all oxidation level is always equal to zero: 2+X-8 = 0. We solve: X = 8-2 = +6. Therefore, the oxidation level of sulfur is equal to +6.

5. One more example: AgNO3. We place: Ag(+1)NO(-2)3. We receive the equation: 1+X-6 = 0. We calculate: X = 6-1 = +5. The required value is found.

Author: «MirrorInfo» Dream Team