Electron Spin

Is there a limit to the number of electrons that an orbital can contain? The answer is, "Yes!" The discovery of the fourth quantum number had implications on how electrons could be arranged in an atom. Unlike the other three quantum numbers, the spin quantum number, $m_s$, is a characteristic of a specific electron rather than a spacial location. Each electron has a quantized spin that is related to the direction of its magnetic dipole. The possible values are $+\frac 1 2$ and $- \frac 12$. Wolfgang Pauli said that no two electrons could have the same four quantum numbers. Since there are only two possible values for $m_s$, this means that there can only be a up to two electrons in an orbital.

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