Electron Configuration Calculator: Full, Noble-Gas and Orbital Diagram for Any Element or Ion

How it works

Electrons = Z − ion charge · fill subshells in Madelung order 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p · capacity of a subshell = 2(2l + 1): s 2, p 6, d 10, f 14 · shell capacity = 2n² · unpaired electrons in a subshell with e electrons and k = 2l + 1 orbitals = e if e ≤ k, else 2k − e

Pick an element and, for an ion, its charge. The calculator places Z − charge electrons into subshells in order of increasing n + l (the Madelung or Aufbau rule), filling each before the next: s holds 2, p 6, d 10 and f 14. It then applies the 20 measured exceptions listed by NIST, such as chromium ([Ar] 3d⁵ 4s¹), copper, palladium, gold and several lanthanides and actinides, where a half-filled or filled d or f set lowers the energy. For a cation it removes electrons from the subshell with the highest n first, and within that shell the highest l, so iron’s 4s electrons leave before its 3d electrons (Fe²⁺ is [Ar] 3d⁶). For an anion it adds electrons to the next open subshell. The output gives the full configuration, the noble-gas shorthand, a copy-friendly plain-text version, an orbital diagram filled by Hund’s rule, unpaired electrons and magnetism, electrons per shell, and the element’s block, period and group. Valence electrons follow the usual group convention: outer s and p electrons for main-group elements, plus the (n−1)d electrons for transition metals; for lanthanides and actinides the inner f electrons are left out. Unlike the effective nuclear charge or Bohr model calculators, this tool builds the whole orbital filling rather than one property. Configurations for elements 104–118 are predictions.

Worked example

Iron has Z = 26, so a neutral atom has 26 electrons. Filling in order gives 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20) and 3d⁶ (26): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, or [Ar] 4s² 3d⁶. The six 3d electrons spread over five orbitals as ↑↓ ↑ ↑ ↑ ↑, leaving 4 unpaired electrons, so iron is paramagnetic. Its shells hold 2, 8, 14 and 2 electrons, it is a d-block element in period 4, group 8, with 8 valence electrons (4s² + 3d⁶). Set the charge to +3 and the two 4s electrons leave first, then one 3d electron: Fe³⁺ is [Ar] 3d⁵ with 5 unpaired electrons.

Sources: NIST: Periodic Table of the Elements, 2024 (ground-state configurations) · Omni Calculator: Electron configuration calculator · Wikipedia: Electron configurations of the elements (data page)

Frequently asked questions