Oxidation Numbers

• Any uncombined element (element not in a compound) has an oxidation number of 0.
• Fluorine always has an oxidation number of -1 in a compound.
• Oxygen has an oxidation number of -2 in all compounds except when it is part of a binary compound with a halogen.
• Hydrogen has an oxidation number of +1 except when it is with metals.
• The algebraic sum of the oxidation numbers in a compound is zero.

EXAMPLE: Find the oxidation number of carbon (C) in Na₂CO₃.

~ Let x = oxidation # of carbon
~ Na’s oxid. # is +1
~ O’s oxid. # is -2
~ sum of (# of each element in cmpd. multiplied by its oxid. #) = 0
~ 2 (+1) + 1 (x) + 3 (-2) = 0
Na C O
~ 2 + x – 6 = 0
~ x – 4 = 0
~ x = +4 (Carbon’s oxidation number in Na₂CO₃ is +4.)

Find the oxidation number of the underlined element in each compound.

1.  KMnO₄

2.  LiNO₃

3.  NaClO

4.  MnO₂

5.  Ca(NO₂)₂

6.  Ba(ClO₄)₂

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