How do I find the oxidation numbers of individual elements in an ion or molecule?

1 Answer
Oct 24, 2016

Answer:

The sum of the oxidation numbers ALWAYS equal the charge on the ion, OR on the molecule....

Explanation:

And of course, if it is a neutral molecule, the sum of the constituent elemental oxidation numbers is ZERO.

Nitrogen oxide, #NO#, is a neutral molecule, and thus the sum of the oxidation numbers must be zero. The oxidation number of #O# is normally #-II#, and it is here. The oxidation number of nitrogen must of course be #+II#, because the sum of the oxidation numbers must equal the neutral charge on the molecule. For #NO_2#, the oxidation number of #N# must be #+IV#. And of course, for #N_2O_5# the oxidation number of nitrogen is?

For nitrous oxide, #N_2O#, the oxidation number of #O# is still #-II#. And for this neutral molecule, the oxidation number of #N# is #+I#, i.e. #1+1-2=0# as required.

Given all this, can you tell me the oxidation number of the metal in #Cr_2O_7^(2-)#?