Calculate an electron configuration
Validate a written electron configuration
Electron-count and orbital rules
For an ion, the electron count is calculated as electrons = atomic number − ionic charge. A positive charge removes electrons, while a negative charge adds electrons. The calculator then places those electrons into available subshells.
Subshell capacity follows 2(2ℓ + 1), giving capacities of 2, 6, 10, and 14 electrons for s, p, d, and f subshells. Orbitals are filled using the Aufbau order, Hund’s rule, and the Pauli exclusion principle. Recognized ground-state exceptions are applied after ordinary filling.
Filling order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
How to use this calculator
- Enter an element using its atomic number, symbol, or full name.
- Enter zero for a neutral atom, a positive number for a cation, or a negative number for an anion.
- Select the preferred notation and choose whether orbital boxes, steps, or the educational excited-state estimate should appear.
- Optionally enter another element and charge to produce a direct comparison.
- Select Calculate configuration, then copy, print, or export the generated result.
- Use the separate checker to test a configuration that you wrote yourself.
Example electron configurations
| Species | Electrons | Full configuration | Shorthand |
|---|---|---|---|
| O | 8 | 1s² 2s² 2p⁴ | [He] 2s² 2p⁴ |
| Na⁺ | 10 | 1s² 2s² 2p⁶ | [Ne] |
| Fe | 26 | 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶ | [Ar] 4s² 3d⁶ |
| Fe³⁺ | 23 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ | [Ar] 3d⁵ |
| Cu | 29 | 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰ | [Ar] 4s¹ 3d¹⁰ |
Understanding the calculated configuration
An electron configuration describes how electrons occupy atomic orbitals. Each term contains a principal energy level, a subshell letter, and an electron count. For example, 3p⁴ means four electrons occupy the p subshell of the third principal shell.
The Aufbau principle normally places electrons into lower-energy orbitals first. Hund’s rule keeps electrons unpaired in equal-energy orbitals before pairing begins. The Pauli exclusion principle limits one orbital to two electrons with opposite spins.
Transition metals need special attention when ions form. Although 4s fills before 3d in many neutral atoms, 4s electrons are usually removed before 3d electrons. This calculator follows that removal convention when positive transition-metal ions are generated.
Some neutral atoms have experimentally favored arrangements that differ from a simple diagonal-rule prediction. Chromium and copper are familiar examples because half-filled or filled d subshells can be especially stable. The calculator includes commonly accepted exceptions throughout the d and f blocks.
Unpaired electrons determine the displayed magnetic classification. A species with one or more unpaired electrons is labeled paramagnetic. A species whose occupied orbitals contain only paired electrons is labeled diamagnetic.
The four quantum numbers identify the differentiating electron’s modeled location and spin. They are derived from the final occupied subshell and a conventional orbital-box ordering. Degenerate orbitals can be labeled differently without changing the physical configuration.
Noble-gas notation shortens a long configuration by replacing inner-shell electrons with a bracketed noble-gas symbol. This form highlights valence and near-valence subshells more clearly. Full notation remains available whenever every occupied subshell is needed.
The excited-state option provides a simple educational promotion model. It moves one electron from the highest occupied subshell into the next available subshell. Real excited states depend on energy, spectroscopy, and allowed transitions, so this estimate is not a measured spectrum.
Ground-state exceptions included
The engine applies recognized adjustments for Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, La, Ce, Gd, Pt, Au, Ac, Th, Pa, U, Np, Cm, Lr, Ds, and Rg. Published sources can differ for a few very heavy elements because their configurations are predicted rather than directly established.
Electron configuration questions
What does an electron configuration show?
It shows how an atom’s or ion’s electrons are distributed among shells, subshells, and orbitals.
Why does 4s fill before 3d?
For many neutral atoms, the 4s orbital is initially lower in energy. Relative energies change as electrons are added and ions form.
Why are 4s electrons removed before 3d electrons?
After the d subshell becomes occupied, 4s electrons are generally higher in energy and are removed first during cation formation.
What is noble-gas shorthand?
It replaces the complete inner-electron configuration with the symbol of the preceding noble gas in brackets.
How are unpaired electrons counted?
The calculator distributes electrons singly across equal-energy orbitals before adding opposite-spin partners.
What makes a species paramagnetic?
A species is paramagnetic when its orbital arrangement contains at least one unpaired electron.
Can the checker prove Hund’s rule from 2p4 notation?
No. Aggregate subshell notation gives electron totals but not individual arrow placement. The checker verifies capacity, order, duplicates, and likely ground-state consistency.
Are heavy-element configurations certain?
Some superheavy configurations are theoretical predictions. The calculator labels its result as an educational model rather than experimental proof.
What does the excited-state option do?
It promotes one electron to the next available subshell as a simplified learning example.
Can an ion have more electrons than its atomic number?
Yes. A negative ion has gained electrons, so its electron count exceeds its proton count.
Educational accuracy disclaimer
This tool is intended for learning and routine chemistry checks. Orbital energies, relativistic effects, excited states, and heavy-element predictions can require advanced quantum calculations. Confirm critical academic or research work with an authoritative chemistry reference.