Oxidation states exceptions, help?

a) NaMnO4


b) K2Cr04


c) HIO4





I'm confused with these because of the exceptions. Thanks in advance.

Oxidation states exceptions, help?
O is almost always -2.


Na, K and H are almost always +1


So, Mn is +7


Cr is +6


I is +7





Watch out for hydrides (H is -1) and superoxides (O is -1)
Reply:Oxygen is most compounds has an oxidation number of -2, as in the cases you listed.


Monoatomic ions have oxidation numbers that are equal to their ionic charge. In the compounds you listed, the sodium would be +1 and the potassium would be +1.


Hydrogen in most cases is also +1, unless it is the hyride ion which is not the in the compounds you listed,


Use the sum rule to determine the oxidation number of the third element. The sum of the oxidation number for a compound must equal zero.


Example NaMnO4


Na +1 Mn = ? O = -2


+1 + ? + 4(-2) = 0


The oxidation number of the Mn would be +7





Try this for the other two compounds.

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