Valence Electrons (2.55)

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Grace Ramey 2K
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Valence Electrons (2.55)

Postby Grace Ramey 2K » Wed Oct 25, 2017 6:42 pm

Can someone explain how we determine which electrons of an atom are valence-shell electrons? I was doing homework problem number 55 from Ch. 2, and some of the answers to the question include electrons in different shells ((n-1)d^10 ns^1 for part d). Wouldn't the valence-shell configuration require n to be the same, since n denotes which shell the electrons are in?

Austin Ho 1E
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Re: Valence Electrons (2.55)

Postby Austin Ho 1E » Wed Oct 25, 2017 8:59 pm

Valence shell electrons are written out following the closest previous noble gas; for Copper it would be [Ar]3d104s1. The part we care about is the 3d104s1. Note that we have a 4s1 and not a 4s2; this is one of the exceptions you need to know for this class (including Chromium). I won't go into detail because Dr. Lavelle covered it in lecture.

Since the question asks about the 'coinage metals,' or the group 11 (Cu, Ag, Au, etc.), we need a generic valence shell form that would apply to all of the group 11 metals.

From the example I provided above, we know that the electron configuration for Cu is [Ar]3d104s1. If we look at the next group 11 element, Ag, we see that its electron configuration is [Kr]4d105s1. Do you see a trend? The electron configuration for the group 11 metals is going to be (n-1)d10ns1. It is written this way because it is generic for all the group 11 metals. If we plug an example, such as Cu, we can see how it works. For Cu, the principal quantum level n is 4 since that's the outermost valence shell. Thus, we get (4-1)d10(4)s1... or 3d104s1, as I showed above. We don't include the [Ar] because this form is generic, and [Ar] wouldn't apply to Ag, Au, etc.

This formula works for all the group 11 metals; for Ag it would be (5-1)d10(5)s1, or 4d105s1, as I showed above again.

We use the 'n' notation because we need a generic formula that applies to all the group 11 metals, as the question asks.

Hope this helps!

Deap Bhandal L1 S1J
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Re: Valence Electrons (2.55)

Postby Deap Bhandal L1 S1J » Wed Oct 25, 2017 11:04 pm

Basically, the (n-1) is used for the d orbital since it is always one level lower in each configuration.

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