Spin orbit coupling is a phenomenon in which the spin and orbital angular momentum of an electron are coupled together. This means that the direction of the electron's spin affects its orbital motion and vice versa.
Spin orbit coupling causes the energy levels of an atom to split into multiple sub-levels. This is because the coupling between spin and orbital angular momentum results in slightly different energies for electrons with different spin orientations.
The filling order for electrons in an atom follows the Aufbau principle, which states that electrons will fill the lowest energy levels first before moving to higher energy levels. This means that the 1s orbital will be filled before the 2s orbital, and so on.
Spin orbit coupling affects the behavior of electrons in a nucleus by causing them to have different energies and therefore different probabilities of being found in different regions of the nucleus. This can impact the stability and reactivity of the nucleus.
The nucleus plays a crucial role in spin orbit coupling as it contains the positively charged protons that interact with the negatively charged electrons. This interaction is what causes the coupling between spin and orbital angular momentum. Additionally, the nucleus also determines the overall energy levels of the atom.