# Subshells

Discussion in 'DAT Discussions' started by Awuah29, Mar 24, 2007.

1. ### Awuah29 Christian predent

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Kaplan pg.213 ( old editon 3rd red book)

Example which fill first, the 3d subshell or the 4s subshell. Dont understand their example. If I have to determine which subshell fills first , I just look at the flowing chart.

Why is 3d n=3 and l=2 and 4s n=4 and l=0
Don't get that part??? Anyone can explain . thanks alot

3. ### DentalKitty

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For 3d, when n=3, the values for l can be from n-1 to 0 so l=2, 1, 0. We know that the d subshell is when l=2. So n+l=3+2=5. For 4s, n=4 so l can be 3, 2, 1, 0. We know that the s subshell is when l=0. So n+l=4+0=4. Since 4 is less than 5 the 4s subshell will fill first. The diagram is also very helpful though and much faster

4. ### DDSDakoo

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Feb 27, 2007
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a good approach also is this
N in is these kinds of problems is the number infront of the letter.
so if you have
WHICH FILLS FIRST 3p or 4s?

In the case of the 3p, it's 3. and in 4s, its 4.
to figure out l: commit s=0, p=1, d=2, f=3 to ur memory.
l is directly correlated to these letters in these problems

So 3p: n=3 and L=1 , following n+l= 3+1= 4

4s: n=4, and L=0, n+l= 4

what 2 do now if they are both the same #?

Go with the one that gives u a lower N. IN THIS CASE, 3p. hope that helps