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From Citizendium, the Citizens' Compendium

An electron configuration specifies the occupancy with electrons of different electron orbitals of an atom or molecule.

Since for low-symmetry molecules the only relevant physical label of an orbital is its energy and orbital degeneracies do not occur, the electron configuration of the ground state of a low-symmetry molecule is simple. It follows from the Aufbau principle: occupy orbitals in increasing orbital energy and take the exclusion principle into account [not more than two electrons per (spatial) orbital].

For high-symmetry cases, such as atoms and linear molecules, where degenerate orbitals do occur, the electron configuration is determined by the Aufbau principle together with Hund's rules.

See atomic electron configuration for a list of electron configurations of the ground state atoms in the periodic table.