Electron Configuration Calculator
Type any element's symbol, name or atomic number and see its full electron configuration and electrons per shell.
| Element | Iron (Fe), Z = 26 |
|---|---|
| Electrons per shell | 2, 8, 14, 2 |
| Valence shell electrons | 2 |
Configuration fills orbitals by energy (1s, 2s, 2p, 3s…); the per-shell count groups the same electrons by main shell (n = 1, 2, 3…) instead.
How to write an electron configuration by hand
- Find the number of electrons: for a neutral atom, that's the atomic number Z.
- Fill orbitals in energy order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d…
- Each orbital type has a capacity: s = 2, p = 6, d = 10, f = 14. Fill each one before moving to the next, stopping once every electron is placed.
Worked example: iron (Fe, Z = 26)
Fill in order: 1s² (2) → 2s² (4) → 2p⁶ (10) → 3s² (12) → 3p⁶ (18) → 4s² (20) → 3d⁶ (26). That gives 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, usually shortened to [Ar] 4s² 3d⁶.
See every electron placed on a Bohr-style diagram in the Electron Lab, or find an element's valence electrons straight from the periodic table in the valence electrons chart.
Frequently asked questions
How do you find the electron configuration of an element?
Fill orbitals in order of increasing energy (1s, 2s, 2p, 3s, 3p, 4s, 3d…) with the element's total number of electrons, writing the shell number, orbital letter and electron count for each one, e.g. 1s² 2s² 2p⁶ for neon.
What does the superscript number mean?
It is how many electrons sit in that orbital. An s orbital holds up to 2, a p orbital up to 6, a d orbital up to 10 and an f orbital up to 14.
Why do some configurations not fill in order of shell number?
Orbitals fill by energy, not shell number: 4s fills before 3d because it is lower in energy for most atoms, which is why potassium is [Ar] 4s¹ rather than having its 19th electron go into 3d.
What is the difference between electron configuration and electrons per shell?
Configuration (1s² 2s² 2p⁶…) groups electrons by orbital and fills by energy order; electrons per shell (2, 8…) regroups the same electrons purely by main shell number n, which is what the Bohr model diagram shows.
