Get any element's full and noble-gas electron configuration, with Aufbau exceptions flagged.
Covers all 118 elements. Known Aufbau exceptions (chromium, copper, palladium and others) are shown with a note.
noble-gas shorthand
How to use this tool
Type its symbol (Fe) or its atomic number (26).
The big line is the noble-gas shorthand, the form most textbooks use.
The metrics show every subshell, so you can count electrons and verify the total.
Chromium, copper, palladium and a few others break the simple Aufbau order for stability — the note says when that happens.
Formula & worked example
Iron (Z = 26): full configuration 1s2 2s2 2p6 3s2 3p6 3d6 4s2, shorthand [Ar] 3d6 4s2, with 2 valence electrons in the outermost shell. Chromium (Z = 24) is the famous exception: [Ar] 3d5 4s1, not 3d4 4s2.
Limitations — read this before you rely on it
Configurations are for neutral atoms in the ground state. Ions differ (transition metals lose s electrons first), and a handful of heavy and f-block elements deviate from the simple Aufbau prediction in detailed experimental data; those cases are flagged in general terms, not silently smoothed over.
Frequently asked questions
How an atom's electrons are distributed across shells and subshells — it determines chemical behaviour.
The inner shells match a noble gas exactly, so [Ar] stands for 1s2 2s2 2p6 3s2 3p6 and only the outer electrons are written out.
A half-filled 3d subshell (3d5) is extra stable, so chromium keeps 3d5 4s1 instead of the expected 3d4 4s2. Copper does the same for a filled 3d10.
Count the electrons in the outermost principal shell. For iron, [Ar] 3d6 4s2, that is the 4s2 pair: 2 valence electrons.
Not directly: an ion has a different electron count. Remove or add electrons to the neutral configuration, remembering transition metals lose their s electrons before d electrons.