- #1

jeebs

- 325

- 4

I have a helium atom in the excited state of (1s,20p), and I am told that it has 4 corresponding atomic terms. I am supposed to "write down the quantum numbers of these 4 atomic terms".

As I understand it, an atomic term is specified by the

^{2S+1}L

_{J}notation, where S is the spin quantum number for the whole atom, L is the orbital angular momentum quantum number for the whole atom, and J is the total angular momentum quantum number for the whole atom.

So, looking at the individual electrons, the 1s electron has spin quantum number s=1/2, and orbital angular momentum quantum number l=0.

the 20p electron has s=1/2, l=1.

I think I am right in saying that only the 20p electron contributes any orbital angular momentum to the atom, so that for the whole atom, L = l = 1, therefore the atomic term should become

^{2S+1}P

_{J}.

However, this is where I start to get confused. My notes aren't that clear and there are a lot of L's, S's J's, l's, s's, j's etc. getting thrown around. How am I supposed to determine what S and J are?

I am assuming there are only 4 possible combinations of S and J. I thought of doing S = s

_{1}+s

_{2}= s+s = 1/2 + 1/2 = 1, therefore M

_{s}= -1,0,1 (not sure if this is relevant) but I was not sure about this and got the impression from my notes this was incorrect. The same goes for saying J=L+S. This would only give me the one atomic term,

^{3}P

_{2}, where I need 4 terms.

I'd appreciate it if someone could help me out here.

Thanks.