The rules for assigning oxidation numbers are in
the Chemist's tools .
Click on the icon
and follow the eleven rules to assign oxidation number to atoms in a chemical
Let's go through the examples below to see how it's
Now let's take a look at sodium nitrate, NaNO3. What
is the oxidation number of nitrogen?
First of all, let's remember what we've learnt:
sodium belongs to group 1A likes to form a +1 charge ion (section
if we forget the charge of the nitrate ion, we can figure it out using the
chemical formula. We know that NaNO3 is a compound
and compounds must be neutral. Since sodium ion is +1, the nitrate ion
(NO3-) must have a -1 charge because we see a 1:1 ratio
of sodium ion to nitrate ion in the chemical formula (see example in section
To determine the oxidation number of nitrogen, we apply
Oxygen is usually assigned an oxidation number
of -2 for oxides. In this case, we have three
oxygen atoms in NO3-.
The sum of oxidation
numbers of an ion or complex ion is the same
as the charge on that ion.
Let the oxidation number of nitrogen be represented as N.
Set up the equation and solve for N.