Quantum number Ms

[MichelleRamirez_2F]

How do we know when the Ms quantum number should be -1/2, or 1/2?

[904936893]

I don't think we would be able to tell. If a question were to come up on quantum numbers, I think all you would need to know about ms is that it can only be +1/2 or -1/2. Whether it is + or - I believe is arbitrary for this class.

[Isabelle Fontanilla 1I]

A specific valence electron must be specified. For example, 2p^6. In this case, the 3 orbitals of the p subshell(px,py, and pz) must be filled accordingly by following the Pauli Exclusion Principle and the Hund's Rule. Distribute the electrons, using up and down arrows to represent the electron spin direction. The first three electrons will be spin up(Pauli), then the last 3 will be spin down(Hund's). Since the indicated electron is the 6th one, it must be spin down, making it a -1/2.

First 3 electrons:
↑ ↑ ↑
__ __ __
px py pz

Last 3 electrons:
↑↓ ↑↓ ↑↓ This electron is the 6th electron (2p^6), as you can see it's spin down, so it is a -1/2.
__ __ __
px py pz

[905096106]

The +1/2 electrons are the first half of electrons in an orbital. For example each orbital is filled by a +1/2 first and then a -1/2 electron