## Quantum numbers

sen117
Posts: 12
Joined: Fri Jan 10, 2020 2:51 pm

### Quantum numbers

Hello,

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.

NS_Tutor_Mathias
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

### Re: Quantum numbers

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.

Edit:
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.