Question

why electron spin????

Answer 1

I don't know your background, so hopefully I'm not making this more confusing than helpful, but electron spin is not necessarily a physical spin. The term was just assigned as a descriptor to satisfy the mathematics describing observed behavior. Spin is really a mathematical designation; it does not (necessarily) mean that the electron is physically spinning in space. It is necessary to accurately provide a full description of the behavior of electrons. It provides explanations for things like magnetism (para, dia, and feremagnetism), as well as energy levels observed in spectroscopy. Spin does not just apply to electrons, but also to protons, neutrons, and other subatomic particles.