Frankly, I think the whole idea of valence electrons with transition metals is nonsense unless the rules make sense and most don't. I've spent almost two hours looking at page after page for an explanation of valence electrons. No two sites give the same rules for transition metals (Cu is a transition metal). The rules are straightforward for groups 1,2,14-18 but not for groups 3-12.
Here is the best site I found but it doesn't agree with other sites about how to treat groups 3-12.
http://www.wikihow.com/Find-Valence-Electrons
I define valence electrons as those in the outside shell. For Cu that is 1 because of the electron configuration which you have correct. And almost all sites agree you don't count FILLED 3d orbitals (which is the case with Cu), then they do count them on groups 3-12. If your key is counting that +1 wrong the author of the key is not defining it the same way. I can understand why 2 might be permissible BUT that isn't the electron configuration ALTHOUGH +1 AND +2 are possible oxidation states. On that basis, the number of valence electrons is +2 for Mn ALTHOUGH it has common oxidation states of +2, +4 and +7 with some others thrown in for good measure. Having said all of that, I think +1 should be the answer; and no, 11 is not right.
I think the confusion is caused by the general idea that most of us have about using the words oxidation state and valence interchangeably and not having set rules about when we count and when we don't count electrons in inner orbitals. Hope this helps and doesn't confuse.
I just need a definitive answer because I've searched everywhere and it's made me second guess my original answer.
How many valence electrons does copper have? I thought it was one but now I'm unsure. I know it's electron configuration is [Ar]4s1 3d10, so that's why I said it was one but then it got marked wrong so is 11 right? 2? I have no idea.
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That's very helpful! Thank you!