## Spin Quantum Number: Test 3

Sabrina Fardeheb 2B
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### Spin Quantum Number: Test 3

For Test #3 question #8, why are the possible quantum numbers both positive and negative 1/2?

I put only positive 1/2 and got it wrong. I thought that unpaired electrons start off with positive 1/2 and then after the orbitals are half filled, then the electrons are spin down. Is this completely wrong? Can the first electron be either spin up or spin down?

Thuy-Anh Bui 1I
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### Re: Spin Quantum Number: Test 3

The question asks "Write all the possible values that a spin quantum number can take for this electron." It can be either +1/2 or -1/2 because the "positive" and "negative" directions are relative. The + and - do not necessarily mean "up" or "down;" they just mean that there are two opposite spins. Therefore, a given electron has a possible spin quantum number of +1/2 or -1/2 because there is no way you can know which one it is unless there is experimental evidence.

Nicole Nikolov 1K
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### Re: Spin Quantum Number: Test 3

There is no way of predicting whether the electron will be spin up or spin down. That is why we should always write +/- 0.5. In addition, question #8 is asking for ALL the possible values for the spin quantum number, so that would include both the positive and negative value.

Ashin_Jose_1H
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### Re: Spin Quantum Number: Test 3

Technically, the first electron can either spin up or spin down. There's no way of identifying which comes first. When drawing the orbital diagram, we typically start off with spin up. We could start with spin down on the orbital diagram and it diagram would follow Pauli's exclusion principle and Hund's rule.