The oxidation number of an atom is the charge that the atom appears to have when the electrons are distributed according to certain rules...

RULES:-

In free elements .e.g N2, each atom has an oxidation number of 0.

The sum of the oxidation numbers of all the atoms in a molecule is 0.

The oxidation number of a simple ion containing one atom is equal to the charge on the ion e.g. oxidation number of Cl- = -1

The sum of all the oxidation numbers of all the atoms in a complex ion is equal to the charge on the ion e.g. a nitrate ion (NO3-) where nitrogen has an oxidation number of +5 and oxygen has an oxidation number of -2, the oxidation number adds up to -1.

Hydrogen has an oxidation number of +1 in its compounds EXCEPT in metallic hydrides where it is -1.

Oxygen has an oxidation number of -2 in its compounds EXCEPT in hydrogen peroxide where it is -1 (H2O2), and when bonded to fluorine it is +2.

The oxidation number of a group 1 element in its compounds is always +1, and of the group 2 elements is always +2.

The oxidation number of a halogen when bonded to a less electronegative atom is -1 (Fluorine is the most electronegative element, and ALWAYS has an oxidation number of -1 in its compounds)

Chlorine has an oxidation number of -1 in compounds where it is not bonded to oxygen or fluorine.

	Created by eimearkelly3 about 11 years ago

Leaving Certificate Chemistry (Oxidation numbers) Note on Oxidation numbers, created by eimearkelly3 on 06/11/2013.