## oxidation number

Posts: 72
Joined: Fri Sep 28, 2018 12:19 am

### oxidation number

how do you find the oxidation number of an element?

Aurbal Popal
Posts: 63
Joined: Fri Sep 28, 2018 12:27 am

### Re: oxidation number

Someone else also asked this question, and this was my response:

I usually figure it out by looking at the periodic table. There is a general pattern:

Group 1 has an oxidation number of +1
Group 2: +2
Group 13 (with Boron): +3
Group 14: +4/-4
Group 15: -3
Group 16: -2
Group 17: -1
Group 18:0

I typically think about it like this: group one elements have one electron, and to get an octet, it will be easier for them to remove that one electron, so it has an oxidation number of +1. Something from group 15, like nitrogen, have five electrons, and will typically want three electrons to complete its octet, so it will have an oxidation number of -3. That is how I remember oxidation numbers.

Hydrogen can either be +1/-1, and oxygen is usually -2, but can be -1 in peroxides.

Metals are typically harder to find out, but if you do the other elements first, you can figure it out by making sure all the charges cancel out (or equal the charge). For example, for SO4 ^(-2), we know that oxygen has an oxidation number of -2. Since there are four oxygens, it has a -8 charge. In order for SO4^-2 to have a -2 charge, Sulfur must have a +6 charge

Cameron_Greenberg_3C
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

### Re: oxidation number

For our purposes in redox problems, the only relevant oxidation numbers are O (-2) and H (+1). These are the only elements coupled with metals, and the metals have an unspecified oxidation number that can be deduced from adding up the oxidation numbers of the O and H ions and then subtracting back to match the overall charge.