Electron Configuration Calculator
Enter an atomic number from 1 to 118 to see that element's ground-state electron configuration, written both in full and using noble-gas shorthand.
Last updated: September 26, 2026
Frequently asked questions
What is the Aufbau principle?
It's the idea that electrons fill the lowest-energy orbitals first, building up an atom's configuration one electron at a time in a standard subshell order (1s, 2s, 2p, 3s, and so on).
What are the Pauli exclusion principle and Hund's rule?
The Pauli exclusion principle says each orbital can hold at most two electrons, with opposite spins. Hund's rule says that within a subshell with multiple orbitals of equal energy, electrons occupy separate orbitals singly before any pairing up, which minimizes electron-electron repulsion.
Does simple Aufbau filling always give the correct configuration?
No. It's correct for most elements, but there are known exceptions, mostly among transition metals (like chromium and copper) and some heavier elements, where a filled or half-filled d or f subshell provides extra stability that changes the actual ground-state configuration.
How is this different from the Atom Calculator?
The Atom Calculator gives you the total number of protons, neutrons, and electrons from Z, A, and charge. This calculator instead shows how those electrons are distributed among subshells and orbitals.
What does noble-gas shorthand mean?
It abbreviates the inner, already-filled shells using the symbol of the preceding noble gas in brackets, then lists only the additional subshells filled beyond that noble gas, which is shorter and easier to read for heavier elements.
Does this support ions?
This calculator covers neutral atoms only. Ion configurations, especially for transition metals, don't always follow the reverse of the neutral-atom filling order (electrons aren't necessarily removed from the last subshell filled), so a robust ion mode needs separate, carefully verified rules not included here.