• Electrons have a unique set of identifiers in the quantum numbers that describe their location and spin.
  • The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers.
  • If those three numbers are identical for two electrons, the spin numbers must be different in order for the two electrons to be differentiated from one another.
  • The two values of the spin quantum number allow each orbital to hold two electrons.
  • The figure below shows how the electrons are indicated in a diagram.
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