19 4.4 Spin quantum number (ms)
- Any orbital can hold at most two electrons.
- Each electron spins about its own axis (like the Earth) while moving around the nucleus.
- Two electrons in one orbital are both negative and might be expected to repel; however, their spins are in opposite directions, creating opposing magnetic fields that attract each other and lower the repulsion.
- They are said to be spin-paired (↑↓).
The spin quantum number determines the direction of spin: clockwise gives ms = +½ (↑), anticlockwise ms = −½ (↓).