Explanation:
For simple ions, i.e.
Na+ , Cl− , Fe2+ , Fe3+ , the oxidation number of the element is simply the charge on the ion.
Explanation:
For more complex ions, the SUM of the oxidation numbers equals the charge on the ion. The sum of the oxidation numbers also equals the charge on the molecule in a NEUTRAL molecule.
Let's consider Cl−, ClO2 , ClO−4 . Typically the oxidation number of oxygen in its oxides is −
II , and it is here in these examples.
Given what I have said the oxidation number of
Cl
in chloride ion,
Cl− , is −I . The oxidation number of Cl in ClO
2 is +IV, and the oxidation number of
Cl
in perchlorate,
ClO−4 , is +VII .
I don't what level you are at. If you are at A level, you simply have to know what I wrote in the opening statement. If you are an undergrad you do have to know how to assign oxidation states in more complicated molecules and ions. Good luck.
