Electron Configuration Calculator
Write the full and abbreviated electron configuration of any element from its atomic number, with the number of valence electrons.
What this calculator does
Enter an element or atomic number and get the ground-state configuration, the noble-gas shorthand and the number of valence electrons.
When you need it
Electron configurations explain the periodic table: why elements group together, which orbitals bond, and why transition metals form ions with different charges.
Formulas
- Aufbau order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
- Each s subshell holds 2 electrons, p holds 6, d holds 10 and f holds 14
How to use it
- Enter the atomic number Z or pick the element.
- Read the full configuration and the abbreviated one.
- Read the valence electrons.
Worked example
Write the electron configuration of iron (Z = 26).
- Fill in order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
- Replace the first 18 electrons with the noble gas: [Ar]
Answer
Iron is [Ar] 3d⁶ 4s², with 2 valence electrons in 4s.
Common mistakes
- Filling 3d before 4s in a neutral atom.
- Forgetting the exceptions, such as chromium [Ar] 3d⁵ 4s¹ and copper [Ar] 3d¹⁰ 4s¹.
- Writing cations by removing electrons from 3d first: the 4s electrons leave first.
Related tools
Frequently asked questions
What is the Aufbau principle?
Electrons fill the lowest-energy orbitals first, following the order 1s, 2s, 2p, 3s, 3p, 4s, 3d and so on.
How do I count valence electrons?
For main-group elements, count the electrons in the outermost shell.
Why are chromium and copper exceptions?
A half-filled or filled d subshell is slightly more stable, so one 4s electron moves into 3d.