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, N20, etc.
2 - oxidation number of a monatomic cation is
same as its charge ( group 1, 2 metals in
particular!) +1, +2
3 – 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 -1
Na2O, 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)