Electron Configuration Calculator
Type an element symbol, name or atomic number to get its ground-state electron configuration in full and noble-gas shorthand, an orbital box diagram drawn with Hund's rule, the number of valence and unpaired electrons, and a shell-by-shell breakdown. Add a charge to get the configuration of an ion.
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e.g. 2 for Fe²⁺, -1 for Cl⁻
How to use the Electron Configuration Calculator
- Enter an element as a symbol (Fe), a name (iron) or an atomic number (26).
- Add a charge if you need an ion, e.g. 3 for Fe³⁺ or -2 for O²⁻; leave 0 for a neutral atom.
- Read the configuration in full and in noble-gas shorthand, plus valence and unpaired electrons.
- Check the orbital diagram to see how electrons fill each orbital; tick the box to include the core.
- Copy the results or download the shell table as CSV.
The Aufbau order and subshell capacities
Electrons fill the lowest-energy subshell available first. The energy order follows the n + l rule: lower n + l fills first, and for a tie the lower n fills first. Each orbital holds two electrons with opposite spins (Pauli exclusion principle), and within a subshell electrons spread out singly before pairing (Hund's rule).
| Subshell | l | Orbitals | Max electrons | First filled at |
|---|---|---|---|---|
| s | 0 | 1 | 2 | H (1s) |
| p | 1 | 3 | 6 | B (2p) |
| d | 2 | 5 | 10 | Sc (3d) |
| f | 3 | 7 | 14 | Ce (4f) |
Filling order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p. A shell with principal number n holds at most 2n² electrons (2, 8, 18, 32…).
Examples and common exceptions
| Element / ion | Shorthand configuration | Note |
|---|---|---|
| Oxygen (O) | [He] 2s² 2p⁴ | 6 valence, 2 unpaired |
| Sodium (Na) | [Ne] 3s¹ | 1 valence electron |
| Iron (Fe) | [Ar] 3d⁶ 4s² | 4 unpaired electrons |
| Fe²⁺ / Fe³⁺ | [Ar] 3d⁶ / [Ar] 3d⁵ | 4s electrons are removed first |
| Chromium (Cr) | [Ar] 3d⁵ 4s¹ | Exception: half-filled 3d |
| Copper (Cu) | [Ar] 3d¹⁰ 4s¹ | Exception: filled 3d |
| Palladium (Pd) | [Kr] 4d¹⁰ | Exception: no 5s electrons |
| Silver (Ag) / Gold (Au) | [Kr] 4d¹⁰ 5s¹ / [Xe] 4f¹⁴ 5d¹⁰ 6s¹ | Same pattern as copper |
| Gadolinium (Gd) | [Xe] 4f⁷ 5d¹ 6s² | Exception: half-filled 4f |
How valence electrons are counted here: main-group elements use the electrons in the outermost shell; d-block elements use ns + (n−1)d; f-block elements use all electrons outside the noble-gas core. Configurations of the superheavy elements (Z > 103) are theoretical predictions.
Frequently asked questions
How do you write an electron configuration?
Fill subshells in order of increasing energy (the Aufbau or n + l rule): 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. An s subshell holds 2 electrons, p holds 6, d holds 10 and f holds 14. Write each subshell with its electron count as a superscript, e.g. oxygen is 1s² 2s² 2p⁴.
What is noble-gas shorthand?
It replaces the inner electrons that match the previous noble gas with that gas's symbol in brackets. Iron, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s², becomes [Ar] 3d⁶ 4s² because argon accounts for the first 18 electrons.
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] 3d⁵ 4s¹ instead of 3d⁴ 4s², and copper is [Ar] 3d¹⁰ 4s¹ instead of 3d⁹ 4s². Several heavier elements such as Mo, Ag, Pd, Pt and Au have similar exceptions; this calculator uses the measured ground states.
How do you find the electron configuration of an ion?
Start from the neutral atom. For a positive ion remove electrons from the highest principal shell first, so transition metals lose 4s electrons before 3d: Fe²⁺ is [Ar] 3d⁶. For a negative ion add electrons to the next open subshell: Cl⁻ is [Ne] 3s² 3p⁶.
How many valence electrons does an element have?
For main-group elements it is the number of electrons in the outermost shell (1 for sodium, 6 for oxygen, 8 for neon). For transition metals the ns and (n−1)d electrons are usually counted together, so iron has 8.
What is Hund's rule?
Within a subshell, electrons occupy each orbital singly with parallel spins before any orbital gets a second electron. That is why nitrogen's 2p³ has three unpaired electrons and why the orbital diagram fills every box with an up arrow first.
What does paramagnetic mean?
An atom or ion with one or more unpaired electrons is paramagnetic and is weakly attracted to a magnetic field. If all electrons are paired it is diamagnetic. Oxygen atoms (2 unpaired) are paramagnetic; neon is diamagnetic.
Are all the tools on FreeToolCabin tested for quality and accuracy?
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