Get the electron configuration of any element or ion in Madelung order, with shells K to Q, valence shell, orbital diagram and quantum numbers.
An electron configuration says how an atom's electrons are distributed over shells and subshells. The Madelung rule (the Linus Pauling diagram taught in Brazil) fills subshells by increasing n + ℓ and, on a tie, by the lower n: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. The s, p, d and f subshells hold 2, 6, 10 and 14 electrons, and shell n holds at most 2n². For iron (Z = 26) the order gives 1s2 2s2 2p6 3s2 3p6 4s2 3d6, or [Ar] 4s2 3d6, with 2, 8, 14 and 2 electrons in shells K, L, M and N. The tool does not rely on the rule alone: neutral atoms come from the NIST ground-state configurations (Z from 1 to 108), and 20 elements in that range depart from the rule, such as Cr ([Ar] 3d5 4s1), Cu ([Ar] 3d10 4s1), Pd ([Kr] 4d10) and Au ([Xe] 4f14 5d10 6s1). For 109 to 118 the configurations are predicted. In ions, electrons leave the outermost shell: Fe3+ is [Ar] 3d5, not [Ar] 4s2 3d3. The tool also shows the orbital diagram by Hund's rule, the unpaired electrons (paramagnetism) and the quantum numbers n, ℓ, mℓ and ms of the last electron.
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Take the atomic number (the number of electrons in the neutral atom) and distribute them over the subshells in Madelung order, filling each to its maximum (s 2, p 6, d 10, f 14). For chlorine (Z = 17): 1s2 2s2 2p6 3s2 3p5, or [Ne] 3s2 3p5, with 2, 8 and 7 electrons in shells K, L and M.
The small number in each box is the filling order and the large one is the number of electrons in the subshell. The arrows follow the diagonals.
Elements up to Z = 108 whose ground state departs from the Madelung filling order. Tap a symbol to open it.
See also: periodic table · molar mass · equation balancer
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