Electron Configuration Calculator
Determine the ground-state electron configuration of any element by atomic number. The calculator applies Madelung (Aufbau) filling order and shows the configuration in standard orbital notation plus a shell-by-shell breakdown.
How does this calculator work?
Electrons fill orbitals in Aufbau order (1s 2s 2p 3s 3p 4s 3d…); s=2, p=6, d=10, f=14 max. Iron (Z=26): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶. About 20 elements (e.g. Cr, Cu) deviate by one electron from ideal Aufbau; this calculator uses the ideal sequence.
Formula
How this is calculated
Electrons fill atomic orbitals in order of increasing energy, following the Aufbau (German: 'building-up') principle. The Madelung rule gives the filling sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. Each s-subshell holds at most 2 electrons, p holds 6, d holds 10 and f holds 14. The Pauli exclusion principle limits each orbital to exactly two electrons of opposite spin, and Hund's rule puts one electron in each orbital of a subshell before any pairing begins.
The calculator fills orbitals in Madelung order, placing electrons one subshell at a time until all Z electrons are assigned. The result is formatted as standard spectroscopic notation (nℓᵉ per subshell, e.g. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶ for iron, Z=26). Electrons are also summed by principal quantum number n to give the population of each shell K (n=1), L (n=2), M (n=3) and so on.
Important limitation: approximately 20 elements have actual ground-state configurations that deviate from ideal Aufbau predictions. The most common deviations occur in the d-block — chromium (Z=24) is [Ar] 3d⁵ 4s¹ rather than the predicted 3d⁴ 4s², and copper (Z=29) is [Ar] 3d¹⁰ 4s¹ rather than 3d⁹ 4s², because half-filled and fully-filled subshells have extra stability. Many lanthanides and actinides also deviate. This calculator uses ideal Aufbau and will differ from experimental data for those elements by one electron.
Frequently asked questions
Aufbau means 'building up' in German. The principle states that electrons occupy the lowest-energy available orbital first. Combined with the Pauli exclusion principle (maximum two electrons per orbital, with opposite spins) and Hund's rule (one electron per orbital before any pairing within a subshell), it predicts the ground-state electron configuration of most elements correctly.
Completely and half-filled d or f subshells have extra stability due to reduced electron–electron repulsion. Chromium (Z=24) adopts [Ar] 3d⁵ 4s¹ instead of the Aufbau prediction [Ar] 3d⁴ 4s², because a half-filled 3d⁵ configuration is more stable. Copper (Z=29) similarly has [Ar] 3d¹⁰ 4s¹. About 20 elements — mostly d- and f-block — deviate from the simple rule.
Valence electrons occupy the outermost shell and govern chemical behaviour — how an element bonds, its reactivity and the types of compounds it forms. Main-group elements have valence electrons in the highest n shell. For transition metals, the partially filled d-subshell electrons also participate in bonding, which is why they can form multiple oxidation states.
TG we-Calculate Editorial Team. (2026). Electron Configuration Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/electron-configuration-calculator
TG we-Calculate Editorial Team. "Electron Configuration Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/electron-configuration-calculator.
TG we-Calculate Editorial Team, "Electron Configuration Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/electron-configuration-calculator
@misc{wecalculate_electron_configuration_calculator, title = {Electron Configuration Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/electron-configuration-calculator}}, year = {2026}, note = {TG we-Calculate} }
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