Oxidations Numbers

[Chloe Shamtob 2H]

Hi, Im confused about the topic of oxidation numbers. What are they and how do you find them? Have we learned them yet?

[Charlie Russell 2L]

Hey, I just answered a question similar to this one!

Here was my answer:

Oxidation numbers, also called oxidation states, are the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom.

An oxidation number can be assigned to a given element or compound by following the following rules:

- The oxidation number of a free element (a chemical element that is not combined with or chemically bonded to other elements like O₂) is always 0.

- The oxidation number of a monatomic ion (such as K⁺ or O^2-) equals the charge of the ion.

- Fluorine in compounds is always assigned an oxidation number of -1.

- The alkali metals (group I) always have an oxidation number of +1.

- The alkaline earth metals (group II) are always assigned an oxidation number of +2.

- Oxygen almost always has an oxidation number of -2, except in peroxides (H₂O₂) where it is -1 and in compounds with fluorine (OF₂) where it is +2.

- Hydrogen has an oxidation number of +1 when combined with non-metals, but it has an oxidation number of -1 when combined with metals.

The algebraic sum of the oxidation numbers of elements in a compound is zero.
The algebraic sum of the oxidation states in an ion is equal to the charge on the ion.

They relate to bonding and charges and this unit is primarily bonding, and my TA said they are fair game on the midterm.

Hope this helps!

(look up a picture or video on oxidation numbers online!)

[Jerry_T]

You can find a guide to oxidation numbers on Sapling (https://sites.google.com/site/chempendix/oxidation). He hasn't gone over oxidation numbers in depth yet.

[Hasan Mirza 3F]

Thanks for the resources and explanations. I was really confused with oxidation #'s.

[Jeremy Wei 2C]

Thanks for the explanation! He didn't go over it really and I was also stuck on oxidation numbers.