Quick answer: how do you write electron configuration?
Electron configuration describes how electrons are distributed among atomic orbitals. It is usually written in a format like 1s² 2s² 2p⁶ 3s² ..., where the number is the principal energy level, the letter s/p/d/f is the subshell, and the superscript is the number of electrons in that subshell.
For iron (Fe, atomic number 26), a common configuration is:
Full electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²
Noble gas shorthand: [Ar] 3d⁶ 4s²This Electron Configuration Calculator can generate the full configuration, noble gas shorthand, shell distribution, and valence electron summary from an element symbol, English name, Chinese name, or atomic number.
How to Use Electron Configuration Calculator
The Electron Configuration Calculator gives you a complete orbital filling breakdown for any element in seconds.
- Enter an element — Type an element symbol (e.g.,
Fe), full name (e.g.,Iron), or atomic number (e.g.,26) into the search field. - View the configuration — The Electron Configuration Calculator displays the full electron configuration using superscript notation (e.g., 1s² 2s² 2p⁶ …) and the noble gas shorthand (e.g., [Ar] 3d⁶ 4s²).
- Explore the summary — Shell distribution, valence electron count, highest occupied subshell, and total electron count are shown in the summary panel.
Exception elements (such as Cr or Cu) are automatically flagged with the corrected configuration and an explanatory note.
Common electron configuration examples
| Element | Atomic number | Full electron configuration | Noble gas shorthand |
|---|---|---|---|
| H | 1 | 1s¹ | 1s¹ |
| C | 6 | 1s² 2s² 2p² | [He] 2s² 2p² |
| O | 8 | 1s² 2s² 2p⁴ | [He] 2s² 2p⁴ |
| Na | 11 | 1s² 2s² 2p⁶ 3s¹ | [Ne] 3s¹ |
| Cl | 17 | 1s² 2s² 2p⁶ 3s² 3p⁵ | [Ne] 3s² 3p⁵ |
| Fe | 26 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s² | [Ar] 3d⁶ 4s² |
| Cu | 29 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹ | [Ar] 3d¹⁰ 4s¹ |
These examples cover main-group elements and transition metals. For elements such as Cr, Cu, Mo, and Ag, the observed stable configuration can differ from the simplest Aufbau filling order, and the calculator shows the exception note automatically.
Formula & Theory — Electron Configuration Calculator
The Electron Configuration Calculator builds configurations using three fundamental quantum-mechanical principles:
Aufbau Principle — Electrons fill orbitals in order of increasing energy:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p →
6s → 4f → 5d → 6p → 7s → 5f → 6d → 7pPauli Exclusion Principle — Each orbital holds at most 2 electrons with opposite spins.
Hund’s Rule — Within a subshell, electrons occupy separate orbitals before pairing.
| Subshell | Max Electrons |
|---|---|
| s | 2 |
| p | 6 |
| d | 10 |
| f | 14 |
The Electron Configuration Calculator applies these rules automatically. For exception elements, the calculator overrides the standard Aufbau result with the experimentally observed configuration (e.g., Cr: [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s² due to extra stability from half-filled d subshell).
How to write an electron configuration
- Find the total electron count - for a neutral atom, this equals the atomic number. Oxygen has 8 electrons; iron has 26.
- Fill orbitals in energy order - start at
1sand follow the Aufbau sequence. - Respect subshell capacity -
sholds up to 2 electrons,pup to 6,dup to 10, andfup to 14. - Check common exceptions - some transition metals adjust 4s and 3d occupancy to reach a half-filled or filled d subshell.
- Convert to noble gas shorthand - replace the closed-shell core with the nearest noble gas symbol to make the result shorter.
Why Exceptions Exist
For transition metals like Cr and Cu, the energy difference between 3d and 4s is small. A half-filled (d⁵) or fully-filled (d¹⁰) d subshell provides extra stability, causing one 4s electron to move into the 3d subshell. The Electron Configuration Calculator explicitly notes these cases with the verified configuration.
Use Cases for Electron Configuration Calculator
The Electron Configuration Calculator supports a wide range of chemistry tasks:
- Chemistry coursework — Students can verify electron configurations for any element in the periodic table using the Electron Configuration Calculator, saving time on homework and exam review.
- Periodic trends analysis — Compare valence electron counts across periods and groups. The Electron Configuration Calculator makes it easy to see why elements in the same group share similar chemistry.
- Transition metal chemistry — Understanding d-electron count is essential for predicting oxidation states, color, and magnetism. The Electron Configuration Calculator provides accurate d-electron configurations including exceptions.
- Spectroscopy interpretation — Electronic transitions and emission spectra relate directly to orbital occupancy, which the Electron Configuration Calculator displays clearly.
- Bonding and reactivity — Valence electrons determine an element’s bonding behavior. The Electron Configuration Calculator highlights these electrons for quick reference.
From hydrogen to californium, the Electron Configuration Calculator provides a reliable, instant reference for orbital structure, making it an essential tool for chemistry education and research.