The Pauli Exclusion Principle& the “Building up Principle”

• Electrons in an atom are arranged in individual “orbitals” each having a set of quantum numbers (n, l, ml, ms)

• No two occupied electron orbitals can have the same set of quantum numbers.

• The electrons in an atoms occupy the set of lowest energy orbitals consistent with this exclusion principle.

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This “building up principle” was a meaningful way to understand the periodic table of the elements, and the fact that it works shows that it contains a least some elements of truth and reality.