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Electron Configuration Calculator

Find the electron configuration of any element, in full and noble-gas shorthand.

About the Electron Configuration Calculator

Electrons fill subshells roughly in order of increasing energy, following the Madelung (n + l) rule: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p… Each s subshell holds 2 electrons, p holds 6, d holds 10 and f holds 14.

A few elements break the simple order because half-filled and filled d and f subshells are especially stable: chromium is [Ar] 3d⁵ 4s¹, not 3d⁴ 4s², and copper is [Ar] 3d¹⁰ 4s¹. This calculator uses the measured ground states (NIST) for those exceptions.

The formula

Fill order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

Worked example

Example: Copper (Cu), Z = 29 = [Ar] 3d¹⁰ 4s¹

  1. Input: Element (symbol, name or atomic number): Cu.
  2. Formula: Fill order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
  3. Result: Copper (Cu), Z = 29 = [Ar] 3d¹⁰ 4s¹
  4. Electrons: 29
  5. Electrons in shell 4: 1
  6. Unpaired electrons (Hund's rule): 1

Questions people ask

What is iron's configuration?

[Ar] 3d⁶ 4s².

Why is 4s filled before 3d?

For neutral atoms up to calcium, 4s is lower in energy; for ions, 4s electrons are removed first.