How do you determine the oxidation number of any element by reading the periodic table

Question

How do you determine the oxidation number of any element by reading the periodic table

Answer 1

Some elements can have only one oxidation number, like the elements in groups IA, IIA and IIIB, (which are +1, +3 and +3 respectively) but other elements can have several oxidation numbers, like many of the transition metals.

For metals, at least one of the oxidation numbers will match the Roman numeral at the top of the column in the PT.  

For nonmetals, there will be one negative oxidation number, which can be determined by subtracting the Roman numeral at the top of the column from 8.  Halogens are -1, chalcogens (O, S, etc) are -2, the nitrogen family is -3, etc.

Other oxidation numbers must be determined experimentally.  If you have the formula of a compound it is possible, by knowing the oxidation numbers of H and O, to deduce the oxidation number of another element.

For instance.  What is the oxidation number of Cr in H2CrO4?  H is +1 and O is -2, and we know that the sum of the oxidation numbers for a compound must equal zero.

+2 +x -8 = 0

+1 +x -2

H2CrO4

solve for x.

x = +6

The oxidation number of Cr in H2CrO4 is +6 which agrees with the Roman numeral at the top of the column in which we find Cr on the periodic table.

Answer 2

In my Periodic Table, the oxidation are written in the top left corner of each box