Oxidation States

[Ariel Fern 2B]

What is the best method to calculating oxidation numbers? What should I look for first? Any tips to calculate it faster? Thanks for any help!

[Daria Azizad 1K]

Elements in Groups 1, 2, 6, and 7 generally will carry the same oxidation state as the charge of the cation/anion they form. Therefore, assigning their oxidation states first allows us to find the oxidation state of an unknown oxidation state. Also, knowing the charges of polyatomic cations and anions will aid in figuring out the overall charge of a molecule and therefore what oxidation state an element must have to achieve that.

[Hui Qiao Wu 1I]

Hydrogens are +1 if bound to nonmetals or -1 if bound to metals.
If oxygen is seen as peroxide (O2), then it's -1; if in any other compounds, it's -2

[Daniela Shatzki 2E]

I agree with what was said above: try to find the elements that generally have the same oxidation states first and assign them their charge so you can then figure out the states of the other elements to make the overall charge zero or satisfy the overall charge of the molecule.

[SVajragiri_1C]

The oxidation number of Group 1 elements is +1, it is +2 for Group 2 elements, halogens are -1 (in binary compounds). The oxidation number of H is usually +1. Using these facts combined with the rule that the sum of oxidation numbers of ions in a compound has to equal the total charge of that compound, work backwards to determine the charge of other ions in that compound.

[Amy Kumar 1I]

Use typically known oxidation states (such as -2 for oxygen) and work backwards from the overall charge to find the oxidation state of the remaining element(s).

[Nohemi Garcia 1L]

There are some things to look out for when finding oxidation states:
1. The oxidation number for an atom in an elemental form is always 0
2.The oxidation number of of all Group 1A metals is +1, and Group 2A is +2, unless they are elemental.
3. Hydrogen is either +1 (when bonded to a nonmetal), or -1 (when bonded to a metal).
4.Oxygen is either -1 (in peroxides), or -2 in all other compounds (this is the most common oxidation number).
5. The sum of all oxidation numbers of all atoms in an ion is equal to the charge of the ion.

[ThomasNguyen_Dis1H]

When looking at oxidation numbers, you really only care about the metal group because that's what is usually oxidized or reduced. First look at oxygen. Oxygen will always be -2 UNLESS it is in peroxide which then it will be -1. Hydrogen for the most part will be +1 unless it is with a cation metal then it's -1. The charge also has to match the total oxidation numbers so it's easy calculating metal cations. Free elements also have oxidation states of 0 (O2, H2, N2).