posted by mike .
DrBob222, thank you for answering my question(s). Sorry for asking repeatedly, I am new to this "posting" stuff. I thought I was asking different persons. Let me rephrase my question. How do I determine which roman numeral to place between the cation and the anion of a metal-nonmetal substance? I think that there must be a rule of thumb that would tell me how VCl3 ends up being Vanadium (III) Chloride and how CrO2 ends up being Chromium (IV) oxide. There must be some kind of relationship between the charges of each element. But I just can't figure out what it is and how to apply it. Can you help me, please?
Here is the relationship: The net charge on any molecule is zero.
CrO2 you know O is -2, there are two O, making a -4 charge, so Cr must have a +4 charge. Chromium(IV) oxide.
Check that on VCl3
Here is a site that gives some rules for determining the oxidation state of an element.