Build the ground-state electron configuration, noble-gas shorthand, shell distribution, and orbital diagram for any element by atomic number. Use it to test different inputs quickly, compare outcomes, and understand the main factors behind the result before moving on to related tools or deeper guidance.
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Build a ground-state electron configuration Enter an atomic number from 1 to 118 to generate the full configuration, noble-gas shorthand, shell distribution, and an orbital-diagram-style filling view.
Enter an atomic number Add a whole number from 1 to 118 to calculate the ground-state configuration and orbital filling.
Electron configuration calculator guide: Aufbau order, orbital diagrams
Electron configuration describes how electrons occupy atomic orbitals in the ground state of a neutral atom. This calculator builds the full configuration, noble-gas shorthand, shell distribution, and an orbital-diagram-style filling view from atomic number while also flagging the common elements that do not follow the simple Aufbau order exactly.
What electron configuration is showing
An electron configuration lists how many electrons occupy each subshell such as 1s, 2p, or 3d. Reading the notation tells you which orbitals are filled, which shell the valence electrons occupy, and where the element sits in the broad periodic-table filling pattern.
This page is designed for neutral atoms in their ground state. It starts from atomic number, which equals the number of electrons in a neutral atom, and then fills orbitals in the standard order before applying known ground-state exceptions where a more stable arrangement is observed experimentally.
The filling order used here
The usual filling sequence follows the Aufbau pattern: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. Within each subshell, the orbital diagram fills one electron into each box before pairing them, which reflects Hund's rule in the simplified notation shown here.
That order is a strong first approximation, but it is not perfect for every neutral atom. Transition metals and heavier elements can shift one electron between nearby subshells to reach a lower-energy ground state, so a good calculator should not treat the naive filling sequence as universally exact.
Worked example: iron and chromium
For iron, atomic number 26, the ground-state configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, which is commonly written as [Ar] 4s² 3d⁶. The shell distribution is 2, 8, 14, 2, and the orbital diagram shows the 3d subshell with six electrons distributed across five d orbitals.
Chromium is a useful exception check. A simple Aufbau-only model would suggest [Ar] 4s² 3d⁴, but the experimentally observed ground state is [Ar] 4s¹ 3d⁵. If a calculator does not account for that kind of exception, it is fine for rough classroom pattern spotting but not for reliable ground-state reference.
Where this model stops
This page is for neutral atoms and ground-state configurations only. It does not calculate ionic configurations, excited states, term symbols, spin-orbit coupling, or spectroscopic notation beyond a simplified orbital-filling view.
The orbital boxes are a teaching aid, not a full quantum-mechanical wavefunction model. They are useful for pattern recognition and periodic-table reasoning, but serious spectroscopy work still depends on experimental reference data and formal atomic-structure methods.
Frequently asked questions
Why does 4s fill before 3d but appear after 3d in shorthand discussions?
The basic filling order places 4s before 3d for many neutral atoms, but once the d subshell is occupied the relative energies become more subtle. That is why shorthand and ion-formation discussions often focus on 3d occupancy and why some ground-state exceptions shift electrons between 4s and 3d.
Why do chromium and copper count as exceptions?
Those atoms gain extra stability from half-filled or filled d subshell patterns. As a result, one electron shifts from 4s into 3d, producing [Ar] 4s¹ 3d⁵ for chromium and [Ar] 4s¹ 3d¹⁰ for copper rather than the naive Aufbau-only result.
Can I use this calculator for ions?
Not reliably. Ionic configurations often remove electrons from the highest-energy occupied shell in a way that differs from the simple neutral-atom Aufbau sequence. This page is intentionally limited to neutral ground-state atoms.
What does the orbital diagram add beyond the configuration string?
The orbital diagram shows how electrons occupy individual orbitals inside a subshell, making Hund's rule and electron pairing easier to see. It is especially useful for understanding p, d, and f filling patterns visually.
