Electron Configuration Calculator

Full and noble-gas electron configuration, orbital diagram, valence and unpaired electrons for any element or ion.

Fill subshells in Aufbau order (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d…) with up to 2, 6, 10 and 14 electrons in s, p, d and f. Iron (26 electrons) is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, or [Ar] 4s² 3d⁶. Cations lose their highest-n electrons first, so Fe²⁺ is [Ar] 3d⁶.

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How to use it

  1. Type an element symbol (Fe), name (iron) or atomic number (26).
  2. For an ion, enter its charge: 2 for Fe²⁺, −1 for Cl⁻.
  3. Read the full and shorthand configuration, the orbital diagram and the unpaired electron count.

What you enter

What you get

Formula

Subshell capacity = 2(2l + 1): s 2, p 6, d 10, f 14 | Filling order by increasing n + l, then n (Madelung rule)

Ground-state exceptions in the d and f blocks (Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, La, Ce, Gd, Pt, Au, Ac, Th, Pa, U, Np, Cm) use measured configurations.

Worked example: iron and Fe³⁺

Input: Fe, charge 0 and then +3

Result: Fe: [Ar] 4s² 3d⁶, 4 unpaired; Fe³⁺: [Ar] 3d⁵, 5 unpaired

Fe³⁺ has a half-filled 3d subshell, which is why it is strongly paramagnetic.

Questions

How do you write an electron configuration?

Count the electrons (the atomic number for a neutral atom), then fill subshells in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. Write each subshell with its electron count as a superscript.

What is the noble gas shorthand?

Replace the inner electrons with the symbol of the previous noble gas in brackets. Sodium, 1s² 2s² 2p⁶ 3s¹, becomes [Ne] 3s¹.

Why are chromium and copper exceptions?

A half-filled or completely filled d subshell is extra stable, so one 4s electron moves into 3d. Chromium is [Ar] 4s¹ 3d⁵ rather than 4s² 3d⁴, and copper is [Ar] 4s¹ 3d¹⁰.

How do you find the electron configuration of an ion?

For an anion, add electrons in the normal filling order. For a cation of a transition metal, remove the outermost s electrons before d electrons: Fe is [Ar] 4s² 3d⁶, Fe²⁺ is [Ar] 3d⁶ and Fe³⁺ is [Ar] 3d⁵.

Limitations

References

More Chemistry

All free tools · By Dr. Zubair Khalid, DVM, MS, PhD.