Determining valance electron of transition metal

[KyoPhan]

I'm confused because I've been seeing different answers. I watched chad's video, and he did some examples for determining # of valance e.

Zn 4s 3d10 Said that the d was full so you just count the s electrons; thus 2 valance e
Cu 4s1 3d10 Said something similar; thus just 1 valance electron

So if the d's are full, you don't count them as valance? How about Ni (4s2 3d8)? Following this rule, it would be 10 valance e? Sc would be 3?

Also, can anyone give me a brief explanation of why you wouldn't count them?

Thanks a lot.

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[FeralisExtremum]

I can't tell you why you don't count them (I assume its because the subshell is stable when full so those electrons wouldn't really be participating in bonds/chemical reactions).

But to answer your other question: when the d-subshell isn't full, you count all the electrons. So Ni would be 10, Sc would be 3, etc.

 

[KyoPhan]

Thank you for confirming!

 

[Darrka]

You only count s and p levels for valence because even if 3d isn't full, it's still at a lower principle energy level than 4s, and is not counted as valence. S and p levels only. I just had my chemistry exam last Thursday and electron configurations was probably the biggest subject on the exam.

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