[tumblewush]

So we were there doing a review on quantum numbers, and somehow I got confused about what my instructor said regarding some of the problems:

What is the maximum number of electrons that an atom can have with each of the following quantum number specifications?
a. n = 3, m_s = -1/2
b. n = 2, l = 0, m_l = 0, m_s = -1/2

My solution:
a. Since only n is given, I go 2n² to find the total number of electrons, which is 18. This 18 involves the -1/2 and +1/2 spin electrons, so I divide 18 by 2 to get 9 electrons that have an m_s of -1/2. For some reason, my instructor says it's 18. He may be right, I'm just confused as to how he got the answer
b. As for this one, since the complete set of quantum numbers are already given, only 1 electron can have this exact address. For some reason, my instructor says it's 2.

What my instructor said is confusing me. Am I right in assuming that for this particular question the orbitals involved are already completely filled? Can anybody shed some light on my confusion?

[AWK]

The problem lays down rather in the precise understanding
all with s=-1/2 - you understanding
all to s=-1/2 (inclusive) - your instructor understanding

Spins are numbered +1/2 and -1/2

[mjc123]

I don't think so. If the question was exactly as quoted, there is no ambiguity. s = 1/2, m_s = +1/2 or -1/2. In this case m_s = -1/2 is specified - there is no question of "inclusive". OP's answers were right, instructor's wrong.

[Borek]

OP's answers were right, instructor's wrong.

+1 on that.