Oxidation Numbers

Jessica Esparza 2H
Posts: 130
Joined: Wed Sep 18, 2019 12:15 am

Oxidation Numbers

Does anyone have any tips for finding oxidation numbers?

Posts: 100
Joined: Wed Sep 18, 2019 12:19 am

Re: Oxidation Numbers

Break the molecule into each of its elements. Then use a periodic table to find the normal charge of each element. Then combine those to find the oxidation number.

Daniel Toscano 1L
Posts: 95
Joined: Tue Nov 13, 2018 12:18 am

Re: Oxidation Numbers

Verity Lai 2K
Posts: 100
Joined: Sat Aug 24, 2019 12:18 am

Re: Oxidation Numbers

The oxidation number is the charge of the element which you can find from patterns on the periodic table. For example, group 1 has an oxidation number/charge of +1.

Angela Patel 2J
Posts: 110
Joined: Sat Aug 24, 2019 12:17 am

Re: Oxidation Numbers

We know common oxidation numbers. For example oxygen always has an oxidation number of 2-. Hydrogen is typically +1. All group 1 metal cations have a charge of +1, etc. You can use these known oxidation numbers to find the oxidation numbers of other elements in compounds with these.

Dina Marchenko 2J
Posts: 54
Joined: Thu Jul 25, 2019 12:16 am

Re: Oxidation Numbers

You're best off memorizing the main rules (ex: O2 is always -2 for this class, group 1 are +1, etc.)

When looking at a compound, first look at the elements that have oxidation number rules and figure out what the oxidation number of a single atom would be. Then multiply that by any subscript or stoichiometric coefficients to get the overall charge of that subunit (if it's cl2, within a compound then the overall charge would be -2 not -1). Once you know this, you can find the oxidation number of the other element(s) of the compound (usually this will be the transition metal). Find a number that combines with the charge you just found to equal the overall charge of the compound (neutral or -1 or +1 or whatever it is). For main group elements (not d block metals) the oxidation number will often coincide with the group number.

Just taking it one step at a time and being precise.

Charlene Datu 2E
Posts: 62
Joined: Wed Sep 11, 2019 12:16 am

Re: Oxidation Numbers

I would also break down the molecule, like someone said previously. By using the periodic table, you can determine the formal charges for the well-known elements. However, for the other elements that you don't know as well, you can find it based off of the other elements in the molecule. The overall charge of the molecule should equal the sum of the charges of all of the elements.

Manav Govil 1B
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

Re: Oxidation Numbers

The oxidation numbers for metals in their natural states are their charges, I believe.

Posts: 97
Joined: Tue Feb 12, 2019 12:15 am

Re: Oxidation Numbers

I like to set it up as if it were an algebraic expression. For example, if we want to find the oxidation number of S in SO4^2-we can set it up algebraically. We know that the overall molecule has to equal -2 and that oxygen has an oxidation number of -2. There are 4 oxygens so we multiply 4 by -2 to get the oxidation number of oxygen. Since S is unknown, we can find it through this equation with S as a variable: S+ 4(-2)=-2 . If we solve for S , we get S=6+ , so 6+ is the oxidation number of S.

Connor Chappell 2B
Posts: 59
Joined: Wed Feb 20, 2019 12:16 am

Re: Oxidation Numbers

Many of the compounds that we deal with in redox reactions contain oxygen, hydrogen, and/or a transition metal, as well as common group 1 elements. Memorizing that Oxygen is 2- and the group 1 elements are +1 can help you identify the oxidation states of the other elements in the compound.