Guys I'm doing uni Chem (but only fundamentals), can I ask a question here?
I'm really confused about the 'difference' between oxidation numbers and ionic charges.
It's clear to me what ionic charges are for standalone ions e.g. Cl-, K+, Ca2+ etc.
Now we have just learned oxidation numbers and their 'rules' which I understand is not the same as the ionic charge - fine.
BUT what seems to happen is that when figuring out the oxidation numbers for individual elements in a compound, sometimes they use the oxidation number 'rules' and sometimes they use the ionic charges. Like my lecturer today said, for some compound that contained Cl, "The Chlorine has an oxidation number of -1 because it does in it's ionic state." but then thats not the case for other elements.
I'm REALLY confused about what to use when here, can anyone help?
Here's an example question that I found an answer to online.
Q: What is the oxidation number of iron in K4Fe(CN)6?
Well from the 'rules' we know that Group I elements will carry +1, so the K4 is +4. That means the net charge of the Fe(CN)6 needs to be -4.
But then the answer goes on to say "CN has a -1 charge. It just does. Hence, CN is contributing -6. "
I know that the polyatomic ion CN has an ionic charge of -1 (CN-) but this just doesn't make sense to me, all of a sudden we are using the ionic charge for the polyatomic ion instead of the oxidation number?