Electron configurations, filled one electron at a time

An electron configuration lists which subshells hold an atom’s electrons. The diagram above draws each subshell as a row of orbital boxes, raised by energy. Press Play and electrons drop in one element at a time, from hydrogen to oganesson. Each arrow is one electron; up and down are the two spin states.

The filling order

Subshells fill in order of increasing n + ℓ, and on a tie the lower n goes first. That is the Madelung rule, and the staircase in the diagram is that rule drawn in 3D:

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p

Three rules decide where each electron goes. Aufbau: lowest energy first. Pauli exclusion: at most two electrons per orbital, with opposite spins. Hund’s rule: inside a subshell, spread out with parallel spins before pairing. Step through carbon, nitrogen, and oxygen and watch 2p go ↑, ↑ ↑, ↑ ↑ ↑, then ↑↓ ↑ ↑.

Exceptions to the Aufbau principle

The rule is a prediction; the ground state is a measurement. For 20 elements in this dataset they disagree, mostly where (n−1)d and ns, or 4f/5f and 5d/6d, are nearly the same energy. Switch to “Madelung rule only” above to see what the rule alone would give.

Electron configuration chart for all 118 elements

Ground-state configurations in noble-gas shorthand, from the same dataset as the interactive periodic table. Each name links to the full element profile. For the shapes of the s, p, d, and f orbitals themselves, see hydrogen orbitals in 3D and why the table is four blocks.

For the heaviest elements, roughly past Z = 100, configurations are calculated predictions rather than spectroscopic measurements — those atoms survive seconds or less, a few at a time.

Electron configuration questions