Electron Configuration Calculator

Generate full electron configurations, noble gas notation, orbital diagrams, and identify valence electrons for any element (1-118) or ion.

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Element categories in dropdown are color-coded:
Alkali Alkaline Transition Metal Metalloid Nonmetal Halogen Noble Gas Lanthanide Actinide
Quick select common elements:
H (1) C (6) N (7) O (8) Na (11) Cl (17) Fe (26) Cu (29) Ag (47) Au (79)
Aufbau Principle: Electrons fill orbitals in order of increasing energy
Order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
Result
What Is Electron Configuration?

Electron configuration describes the distribution of electrons in an atom's orbitals. It follows three key principles:

Key Principles
  • Aufbau Principle: Electrons fill orbitals from lowest to highest energy
  • Pauli Exclusion Principle: Each orbital holds max 2 electrons with opposite spins
  • Hund's Rule: Electrons fill degenerate orbitals singly before pairing
Orbital Capacity
  • s orbitals: 1 orbital, max 2 electrons
  • p orbitals: 3 orbitals, max 6 electrons
  • d orbitals: 5 orbitals, max 10 electrons
  • f orbitals: 7 orbitals, max 14 electrons
Noble Gas Notation

A shorthand that uses the previous noble gas in brackets, followed by the remaining electron configuration. For example, Fe (26 electrons): [Ar] 4s² 3d⁶

Worked Examples

1) Carbon (C, Z=6)

Full: 1s² 2s² 2p²

Noble gas: [He] 2s² 2p²

Valence: 4 electrons (2s² 2p²)

2) Iron (Fe, Z=26)

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶

Noble gas: [Ar] 4s² 3d⁶

Valence: 2 electrons in 4s (d electrons are not valence for transition metals)

3) Iron(II) Ion (Fe²⁺, Z=26, charge=+2)

Remove 2 electrons from highest energy level (4s before 3d for ions)

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶

Noble gas: [Ar] 3d⁶

Exceptions to Aufbau Principle

Some elements have unexpected configurations due to orbital stability:

  • Chromium (Cr, Z=24): [Ar] 4s¹ 3d⁵ (not 4s² 3d⁴) - half-filled d subshell is more stable
  • Copper (Cu, Z=29): [Ar] 4s¹ 3d¹⁰ (not 4s² 3d⁹) - filled d subshell is more stable
  • Silver (Ag, Z=47): [Kr] 5s¹ 4d¹⁰
  • Gold (Au, Z=79): [Xe] 6s¹ 4f¹⁴ 5d¹⁰
Quantum Numbers
Quantum NumberSymbolDescribesValues
PrincipalnEnergy level/shell1, 2, 3, 4...
Angular momentumlSubshell shape0 to n-1 (s=0, p=1, d=2, f=3)
MagneticmlOrbital orientation-l to +l
SpinmsElectron spin+½ or -½

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