How do you know the charge of polyatomic ions?

Oxidation state assignment rules and procedures, how to treat polyatomic ions in neutral compounds.?

• Greetings, What exactly is the procedure for dealing with polyatomic ions within a neutral compound? I.e. AgNO3 I do know that Ag's oxidation state is +1 but I did not initially want to assign it this way based on the empirical rules that want me to first assign oxygen, then the 5A element nitrogen and then Ag. My question is as follows: Does the oxidation for Ag come form the fact that, although it is not a 1A element, it's +1 charge is predictable (much line Zn^2+ or Sc^3+). Or does this oxidation from the fact that I treat NO3 as a nitrate unit = -1 (This seems flawed to me, but I'm just not certain and my references aren't clarifying). I guess ultimately: 1) In a large compound that has a polyatomic ion embedded in it, do I follow the oxidation assignment as if I didn't know it were there (i.e., just let the element oxidation flow chart take over) 2) Is Ag an exception not listed in the general empirical rules for oxidation assignment? One that acts like a group IA?

• Answer:

  Here is the way I do this. Simply check the oxidation numbers for silver and the nitrate ion Plus one silver, - one nitrate ion. Then examine the nitrate ion knowing that the oxidation number for each oxygen atom is a -2 most of the time, so three time -2 would be a total charge of -6 on the three oxygen ions, so then ask yourself what would the charge on the nitrogen have to be to bring the overall charge on the nitrate ion down to -1. Of course it would have to be a plus 5.