Oxidation and Reduction!

Aka: Redox

• Oxidation and Reduction is the concept that helps us understand how/why elements gain/ lose electrons

• An important Mnemonic is:• LEO says GER• Lose electrons= oxidation, Gain electrons =

Reduction (OilRig…) idonlike

Oxidation state/number

• The oxidation number of an element is *kind of like the charge.

• We have learned that certain elements always have “a” charge!

• Well… Guess What!!!! (That’s a Bingo!!!)

• Sometimes the charges of elements can change, and/or be different from what we expected. ( yes… that IS exciting!!!)

Oxidation numbers of elements:

Oxidation Rules:1 - oxidation state of a free ( single) element (or diatomic molecule) is 0 Na0, Fe0, N2

0, etc.

2 - oxidation number of a monatomic cation is same as its charge ( group 1, 2 metals in particular!) +1, +23 – normal oxidation number of Hydrogen is +1

but… H -1 in metal hydrides NaH, MgH2,

4 – oxygen is usually -2, but in peroxides it is -1Na2O, MgO, H2O, Na2O2, MgO2,H2O2,

5 – a lot of elements- especially transition metals and most of the non metals can have lots o’ different oxidation numbers

And that sounds fascinating … doesn’t it? (yes!)

*The sum of all oxidation numbers in a compound will = 0 , kinda like what we have been doing with ionic compounds ( examples!)And : NO, NO2,N2O5, etc….

The sum of all oxidation numbers in a polyatomic ion will be the charge of the P.A. ion(examples)…

Examples:

Some, like transition metal ionic compounds you can do!Examples:Molecular compounds we have to figure out, based on rules. ( examples…)Polyatomic ions… we have to figure out based on rules… (examples)