Gchem: rules for Oxidation states/polyatomic ions?

[mcdds75]

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anyone have some good rules for remembering Oxid #'s and rules? Polyatomic ions kill me for some reason, any suggestions?

 

[SupahShyGuy]

anyone have some good rules for remembering Oxid #'s and rules? Polyatomic ions kill me for some reason, any suggestions?

For polyatomic ions, just look at the anions first, you need to establish the degree of negative charge before the positive charge. In MnO4-, look at the oxygens, each one is 2- and there are 4 oxygens making a total charge of 8-. The overall charge of MnO4- is 1- therefore the Manganese cation should be 7+; (😎+(7) = -1 overall charge.

 

[NumbaOneStunna]

1. Elements = 0 Oxidation State (like H2 or O2)
2. Group 1 or 2 Metals get +1 ox or +2 ox respectively
3. H is +1 unless bound to a metal then it's -1
4. More Electronegative Atoms get their normal oxidation numbers (their group number minus 8, so a halogen gets -1 and oxygen would get -2)
5. Leave the last atom to balance out the overall charge. If it's a polyatomic ion and say the charge is -4 then the sum of all the ox states of each atom must equal -4. So if we have 4 atoms in a molecule with a charge of say -2 and we apply the rules above to get the ox states of three atoms the fourth atom would be X where -2 = sum of ox states of three atoms + X.

 

[mcdds75]

thanks, kind of a stupid question I guess? I haven't had GC in a long time, but I found some resources to help as well!!

 

[NumbaOneStunna]

Not stupid at all mate, I didnt know this stuff until like 2 months ago. Luckily (well actually now not really ), I took Gen Chem in college on pass/fail so I never really tried.