COMPOUNDS

5.10 - Oxidation Numbers

5.10.1 - Assignment of Oxidation Numbers

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 formula.

Let's go through the examples below to see how it's done.

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 4.6)
• 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 5.9)

To determine the oxidation number of nitrogen, we apply

Let the oxidation number of nitrogen be represented as N. Set up the equation and solve for N.

The apparent charge on nitrogen is +5.

Section 6.3
Oxidation Numbers. Calculating Oxidation Numbers ..p121

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