Oxidation Number

[Mrudula Akkinepally]

Can someone explain to me how to calculate the oxidation number and what it means?

[Claire_Latendresse_1E]

Hi! There are a few rules that are good to know. I attached a photo with the rules that I use.
Here's an example of how I work through an oxidation number problem (I hope it works for you):
For CO2, I know that oxygen's oxidation number is -2 (the fifth rule in the picture). Because there are two oxygens, the oxygens contribute a total charge of -4 to the molecule.
Because the molecule is not an ion, I know that the net charge must be 0. So, carbon must have an oxidation number of +4 in order to cancel out the oxygen's charge of -4 (0 = x - 4, so x=4).
Here's how I would go through an oxidation number problem with an ion:
For NH4(+), I know that hydrogen's oxidation number is always +1 (the first rule in the picture). Because there are four hydrogens, they contribute a total charge of +4 to the ion.
The ion has a charge of +1, so carbon must have a charge of -3 to bring down the hydrogen's charge of +4 (1=x+4, so x= -3).
I hope this helps!

[Tanya Nguyen 1B]

Oxidation numbers tell you of electrons are lost or gained. The chart posted above is a good reference. For neutral compounds (no charge) all the oxidation numbers should add up to 0. For ions, all the oxidation numbers should add up to the charge of the ion. Then for free elements its oxidation number is 0.

[Mrudula Akkinepally]

That helps a lot, thank you !

[David He]

In the sampling question you can click "hint" on the top then you will get a link to explanation!