Quantum numbers

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Joined: Fri Jan 10, 2020 2:51 pm

Quantum numbers

Post by sen117 » Tue Jan 28, 2020 5:54 pm


Could you please help me better understand the Quantum numbers?:

I got confused after trying to come up with my own example. Let's say principal quantum number n=4 (which is also the same as the 4th period). Looking at Ca and Cr, the Ca doesn't have d suborbital whereas Cr does. If azimuthal quantum number l=n-1 holds true, then will both Ca and Cr be l=3? I thought l=means the atom contains f suborbital.
To summarize my confusion,
1. I am confused about how n can be the same for both Cr and Ca when they don't have the same subgroups.
2. what am I missing with atoms in period 4 (n=4), why is l=3 when they don't have f suborbital.

Please clarify. I appreciate your help in advance!
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

Re: Quantum numbers

Post by NS_Tutor_Mathias » Wed Jan 29, 2020 1:02 pm

So I think the biggest point of confusion for you is that quantum numbers don't describe elements. They describe electrons: Every electron can be described by 4 quantum numbers.

So calcium for instances has
2 electrons at n = 1
8 electrons at n = 2
8 electrons at n = 3
2 electrons at n = 4

And those last two electrons happen to be at l = 0 and ml 0. One will have a spin (ms) of -1/2 the other +1/2. But at the 3n energy level, we can find both two l = 0 (3s) and six l = 1 electrons (3p) (still no l = 2, since that would be 3d, which is not filled).

So to recap: Every single electron can, individually, be described by a set of 4 quantum numbers.

As an exercise, determine the 4 quantum numbers for the only electron in the valence shell of elemental potassium. Then as a challenge, determine the 4 quantum numbers for every electron in the valence shell of elemental carbon.
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