OK here is the thing I am taking a basic chemistry class and am not sure our instructor knows what she is talking about and neither does the rest of the class.. We have a test next week and are working on Oxidation and Reduction.. When you are assigning O.N numbers to elements how do you figure them out?? I figured the you need to know the possitive and negative charges of all the elements according to the group they are in.. In class she gave us the charges for groups 1A, 2A, 4A, 5A, 6A, AND 7A.. (Which was wrong the first time she gave them to us) She told us that they were going to be the only ones we will need to know but she gave us a take home test and well all the ones from 3B-3A are on the test.. When we told her that she didn't go over that and that we could not find it in the book she told us to google it and I tried that with no success.. Can someone please help me out.. Thank you sooo much..