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I'm a little confused about when d-orbital electrons count as valence electrons. For example, in problem 2A1, Sb is considered to have 5 valence electrons. I assume those electrons are the 3 in the 5p shell and the 2 in the 5s shell. If that is the case, the 10 4d electrons are not considered valence. However, also in problem 2A1, Mn is considered to have 7 valence electrons. That has to be both the 2 electrons in the 4s shell and the 5 electrons in the 3d shell, right? Why are the d-shell electrons counted as valence for Mn and not Sb? Is it just because the d sub-shell is full in Sb and not in Mn?
This would be correct. To the best of my understanding, valence electrons are those that when we draw are a part of an energy level that has not been fully occupied. Therefore, in the one where the d is already full they do not count for valence electrons but because in the other the d is not completely full, it will still continue to count as valence electrons as they are active in bonding. The reason for this is, for it to be a valence electron it would have to be able to interact with other valence electrons and if the subshell's orbitals are full there is no possible manner through which they could interact as they are already stable. Hope this helps!
I think it has to do with the d orbital being a lower energy level when it is full, so its no longer a valence shell.
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