How to determine atom oxidation level in connection

How to determine atom oxidation level in connection

Atom, forming a chemical bond with others, can become a positively charged or negatively charged ion. It depends on that how many electrons it will give to the next atoms, or, on the contrary, will attract to itself. The quantity of the given or attracted electrons characterizes such concept as oxidation level. That is, if atom gave one electron, its oxidation level will be +1. And if it accepted two others electrons, then its oxidation level will be-2.

It is required to you

  • - Mendeleyev's table;
  • - table of electronegativity of elements.


1. Write down an exact chemical formula of connection. Let's say you have such substances which part oxygen is: O2, Na2O, H2SO4. That is oxygen, oxide of sodium and sulfuric acid. What will be the oxidation level of each element in each connection? There is a rule: (that is, consisting of atoms only of one element) the oxidation level of each of these atoms is equal in simple connection to 0. Therefore, the oxidation level of atoms of oxygen is equal in diatomic molecule O2 to 0.

2. The reason of it is obvious. Oxidation level can be other than zero only if electronic density is displaced from the center of symmetry of a molecule aside. And identical atoms have absolutely identical properties, therefore, electronic density cannot be displaced.

3. The molecule of oxide of sodium consists of two elements: alkaline metal of sodium and gas-nonmetal of oxygen. In whose party will the general electronic density is displaced? At sodium on an external electron layer only one electron, and to it is much simpler to give this electron, than to attract to itself seven more (for transition to a steady configuration). At oxygen – six, to it two more others electrons are much simpler to accept, than to give six. Therefore, each of two atoms (more precisely, ions) sodium in this connection will have oxidation level +1. And oxygen ion, respectively,-2.

4. Now consider a formula of sulfuric H2SO4 acid. It consists of three elements: hydrogen, sulfur and oxygen. All of them are nonmetals. Hydrogen as the very first element of the table of Mendeleyev having the one and only electron will show oxidation level +1 (it can only give this electron to other atom). Therefore, total oxidation level of hydrogen +2.

5. Oxygen – more electronegative element, than it is gray (you can check it according to the table of electronegativity) therefore it will accept others electrons, its oxidation level will be equal-2, and total-8. What oxidation level of sulfur? There is one more rule: total oxidation level of all elements taking into account their indexes is equal in connection to 0. Means, sulfur oxidation level + 6.

Author: «MirrorInfo» Dream Team