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.

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Leaving Certificate Chemistry (Oxidation numbers) Notiz am Oxidation numbers, erstellt von eimearkelly3 am 06/11/2013.