問題關於量子力學和電子

You need to distinguish betwween electrons in the free state and electrons in the bound state. Electrons in atomic orbits are in a bound state.

In quantum mechanics, electrons belong to the class of particles called "fermions", which obey the Pauli Exclusion Principle. Briefly speaking, no two electrons (fermions) can possess the same energy (more exactly, the same quantum state). This principle governs the distribution of electrons in orbits of an atom.

In the ground state of an atom, electrons fill all lowest possible energy states (i.e. orbits). Since an electron has two spins (+ve and -ve, which indicates the direction of spin), an orbital level (termed an energy level in quantum mechanics) can only accommodate at most two electrons in order to comply with the Pauli Exclusion Principle.

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