Four calculators, one panel.
Pick a mode below — choose any element from hydrogen to oganesson, and every result explains itself.
Pick any of the 118 elements, from hydrogen to oganesson.
The neutral element the ion is formed from.
Positive for cations (e.g. 2 for Fe²⁺), negative for anions (e.g. -2 for O²⁻).
n = 1 is the shell closest to the nucleus (the K shell).
Ground-state atom — unpaired electrons follow Hund's rule.
Two inputs to an answer.
No manual required — but here's the entire flow in four moves.
Pick a mode
Element for a plain configuration lookup. Ion configuration for a charged species. Shell capacity for the 2n² reference. Unpaired electrons for magnetism.
Choose an element
Pick from the dropdown — every element from hydrogen to oganesson is listed by symbol and name. The example chips jump straight to a common one with one tap.
Read the results
The headline answer sits up top in large type. Related details — block, period, group, shells — sit below, and the full configuration or explanation sits at the bottom.
Trust the checks
Impossible inputs — a charge bigger than the element has electrons for, or a shell number outside 1–7 — get flagged with a plain-English reason. Copy any result set with one click.
The rules behind every answer.
Every mode above comes from the same handful of principles that govern how electrons fill an atom.
Aufbau principle
Electrons fill the lowest-energy subshells first, in this fixed order — with a handful of well-known exceptions like chromium and copper.
Shell capacity
Shell n = 1 holds 2 electrons, n = 2 holds 8, n = 3 holds 18, and so on.
Subshell capacity
Each subshell type holds 2(2l + 1) electrons, where l is 0 for s, 1 for p, 2 for d, and 3 for f.
Questions people actually ask.
The short answers — with the long ones one tap away.
How do I write an electron configuration?+
List each occupied subshell in order of increasing shell number, with the electron count written as a superscript — oxygen, for example, is 1s² 2s² 2p⁴. Electrons fill subshells following the Aufbau principle: lowest energy first, then Hund's rule and the Pauli exclusion principle within each subshell.
What is noble gas (shorthand) notation?+
It replaces the electrons an element shares with the nearest smaller noble gas with that gas's symbol in brackets, then lists only what's left. Iron's full configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s², which shortens to [Ar] 3d⁶ 4s² since argon covers the first 18 electrons.
How do I find the electron configuration of an ion?+
For a cation, remove electrons from the highest principal shell first — for transition metals that means ns electrons leave before (n-1)d electrons, even though d fills after s. For an anion, keep adding electrons in the normal Aufbau order until the extra charge is accounted for. The Ion configuration tab does this automatically.
How many electrons can each shell and subshell hold?+
A shell with principal quantum number n holds up to 2n² electrons. Within it, an s subshell holds 2, p holds 6, d holds 10, and f holds 14 — each following 2(2l+1). The Shell capacity tab breaks this down for any n from 1 to 7.
What is the Aufbau principle?+
It states that electrons occupy the lowest-energy orbitals first, filling subshells in the order 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. A handful of elements, like chromium and copper, deviate slightly because a half-filled or fully-filled d subshell is more stable — this calculator accounts for all of the known exceptions.
How do I know if an element is paramagnetic or diamagnetic?+
Count the unpaired electrons in its ground-state configuration using Hund's rule, which fills every orbital in a subshell singly before pairing any of them up. One or more unpaired electrons means the atom is paramagnetic; every electron paired means it's diamagnetic. The Unpaired electrons tab works this out — and shows the orbital-by-orbital breakdown — for any element.
Is this tool free, and where does my data go?+
It's completely free and runs entirely in your browser — nothing you type is uploaded, logged, or sent to any server. No account, no sign-up, no limits.