# Thread: Quantum numbers and Aufbau principle

1. Maybe someone asked this before, but I've searched on this forum and found nothing that can help me.
My question(s):

I know the Bohr model isn't totally right and that electrons are in orbitals (s, p, d, f..).
The exact location of an electron is being specified with 4 quantum numbers:
n I get that one, say n=4
l Dot get that exactly, but I know that when n=4, the possibilities for l are 0,1,2 and 3
m For every l: all integers bitween -l and +l
s +1/2 or -1/2 something with the spin?

I don't know if it is really necessary to know what those quantum nubers exactly are?

Okay, now they're named by 1s, 2s, 2p, 3s etc.
are they named like the numbers 1s, 2s, 2p, 3s are the n's?
and the letters, 1s, 2s, 2p, 3s are the l's? (l=0 -> s, l=1 -> p, etc?)

If that's right, I think i get that.
My last question, Aufbau priciple, I think it's so weird
why has for example 3d a higher energy level than 4s? and does someone have a hint how you can remember that?
I'm also wondering how you must distribute the electrons in the orbitals (say, you're working with O (8 electrons)), I know it has something to do with the quantum numbers, but what?
I hope someone has enough time to help me out.

2.

3. AufBau =>
It's actually pretty simple... the orbitals are s, p, d and f respectively. Such that s < p < d < f. So the d-orbital, either of any shell, will have a higher energy level than s-orbital. Simple ^_^

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