Calculating oxidation state

[DangerRoss]

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Q1) For a compound like KMnO4, how do we calculate the oxidation state of each atom?

Should we first assume that all alkali metal is +1, all alkali earth metal is +2, and oxygen has -2 state, and then calculate the state of transition metal using these information? So then the compound above Mn will have oxidation state of +7.

Q2) I'm then confused as to if KMnO4 is an "ionic compound" or "chelated compound" where Lewis acid (K or Mn) is surrounded by Lewis base (Oxygen). How do you distinguish the two? Thanks in advance.

 

[axo86]

Hi dangerross,
The rules you suggested are generally correct and it's completely true that manganese has 7+ oxidation state in the permanganate ion. If you ever get stuck or confused with those rules, there is another method you can use where you determined the oxidation state directly from a Lewis structure. Once you have the correct structure, just imagine "giving" all the electrons in every bond in your structure to the more electronegative atom. So if you tried this for permanganate, every oxygen would end up with 8 electrons (6-8= -2 oxidation state) which would confirm what you already stated. (You can see an example of this method here: wiki carbon dioxide example )