Quantum Numbers for Helium’s 1s2 Electrons

Quantum Numbers for Heliums 1s² Electrons

Helium has the electron-configuration diagram 1s². The 1 in the  electron-configuration diagram identifies the principal quantum number: n=1. The s in the electron-configuration diagram identifies the azimuthal quantum number (): =0. The azimuthal quantum number for any s sublevel has just m = 0. See figure 1. Since helium has one s  orbital, the two electrons are in that one orbital. However, they must have opposite spin to occupy the same orbital: ms=+½ for an arrow up and ms=-½ for an arrow down. The quantum numbers (n, , m, ms) for the two electrons are: 1, 0, 0, +½ and 1, 0, 0, -½.   

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