Electron Configuration Calculator

Compute ground-state electron configurations, noble gas shorthand, and valence electrons for any element (Z=1–118). Interactive visualisation of quantum shell filling — perfect for chemistry students, educators, and researchers.

H (Z=1)
O (Z=8)
Fe (Z=26)
Cu (Z=29, exception)
Ag (Z=47)
Au (Z=79)
U (Z=92)
Og (Z=118)
Privacy assured: All calculations run locally in your browser – no data transmitted.Enter any integer between 1 and 118 (Hydrogen to Oganesson).

Understanding Electron Configuration

Electron configuration describes the distribution of electrons in atomic orbitals. It follows fundamental quantum rules: the Aufbau principle (electrons fill lowest-energy orbitals first), Pauli exclusion principle (each orbital holds max 2 electrons with opposite spin), and Hund's rule (electrons singly occupy degenerate orbitals before pairing).

Orbital energy ordering (n+l rule): 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p …

? Quantum Shells & Subshells

  • s-subshell (l=0): 1 orbital, max 2 e⁻
  • p-subshell (l=1): 3 orbitals, max 6 e⁻
  • d-subshell (l=2): 5 orbitals, max 10 e⁻
  • f-subshell (l=3): 7 orbitals, max 14 e⁻

This calculator implements ground-state configurations for all 118 elements, including special exceptions due to enhanced stability from half-filled or fully filled subshells (e.g., Cr, Cu, Mo, Ag, Au, Np, Cm). The data follows IUPAC-recommended values and peer-reviewed literature.

? Real‑world Applications

  • Chemistry & Bonding: Predicts chemical reactivity, oxidation states, and magnetic properties.
  • Materials Science: Guides semiconductor design and alloy behavior.
  • Spectroscopy: Interprets emission/absorption lines.
  • Quantum Computing: Understanding electron states for qubit design.
Real‑life example: Europium (Eu, Z=63)

Europium has configuration [Xe] 4f⁷ 6s². The half‑filled 4f subshell provides extraordinary stability, making Eu²⁺ common in phosphors for LED and fluorescent lamps. This calculator instantly reveals why such rare earth elements exhibit unique optical properties.

Relativistic effect: Gold (Au, Z=79)

Gold's configuration 6s¹ 5d¹⁰ (instead of 6s² 5d⁹) arises from relativistic contraction of the 6s orbital. This makes gold the only metallic element with a non‑silvery colour (yellow‑orange) and high resistance to tarnish – a direct consequence of its electronic structure.

? Historical & Theoretical Foundation

The modern electron configuration model builds on Niels Bohr's atomic model, Erwin Schrödinger's wave equation, and Wolfgang Pauli's exclusion principle. The Madelung rule (n+l rule) was empirically derived to explain the periodic table's structure. The exceptional configurations (like Cu [Ar]4s¹3d¹⁰ instead of 4s²3d⁹) were explained through interelectronic repulsion and exchange energy, validated by atomic spectroscopy. Our calculator respects all known ground-state anomalies up to element 118, conforming to authoritative sources like NIST Atomic Spectra Database and CRC Handbook.

? How to Use the Calculator

  1. Enter an atomic number (1–118) or click one of the preset element buttons.
  2. Press "Generate" – the full electron configuration, noble gas shorthand, valence electrons, and block/period/group appear instantly.
  3. Visual orbital tiles display each subshell's electron count; the canvas shows Aufbau filling order with filled/last/upcoming states.
  4. Use the copy button to export configuration for reports or study notes. Click "Verify at NIST" to cross‑check with official atomic data.

⚡ Common Exceptions & Validation

Element (Z) Expected (naive) Actual ground state Reason
Chromium (24) [Ar] 4s² 3d⁴ [Ar] 4s¹ 3d⁵ Half-filled d-subshell stability
Copper (29) [Ar] 4s² 3d⁹ [Ar] 4s¹ 3d¹⁰ Filled d-subshell
Molybdenum (42) [Kr] 5s² 4d⁴ [Kr] 5s¹ 4d⁵ Half-filled 4d
Palladium (46) [Kr] 5s² 4d⁸ [Kr] 4d¹⁰ Filled 4d subshell
Silver (47) [Kr] 5s² 4d⁹ [Kr] 5s¹ 4d¹⁰ Filled 4d + 5s¹
Gold (79) [Xe] 6s² 4f¹⁴ 5d⁹ [Xe] 6s¹ 4f¹⁴ 5d¹⁰ Relativistic effects + filled 5d
Neptunium (93) [Rn] 5f⁵ 7s² [Rn] 5f⁴ 6d¹ 7s² Enhanced stability (f⁴)
Curium (96) [Rn] 5f⁸ 7s² [Rn] 5f⁷ 6d¹ 7s² Half-filled f⁷ stability

Our algorithm uses an exhaustive internal exception library verified against IUPAC Technical Reports and the NIST Atomic Spectra Database, ensuring scientific rigor.

Myth vs Fact: “4s is always lower in energy than 3d”
Myth: The 4s orbital is always filled before 3d. Fact: For neutral atoms, 4s is indeed lower in energy only when empty. Once occupied, 3d falls below 4s. That’s why we write 3d before 4s in the final configuration (e.g., Fe: 3d⁶ 4s²). This calculator respects the correct final ordering.

? Frequently Asked Questions

The 4s orbital has lower energy only when empty. Once occupied, 3d falls lower in energy. By convention, we write orbitals in order of increasing principal quantum number (3d before 4s) for neutral atoms.

Some elements (Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, Pt, Au, Np, Cm, etc.) deviate from the Aufbau order because a half-filled or fully filled subshell provides extra stability. Our calculator automatically handles these 25+ exceptions.

Predictions for elements 104–118 are based on relativistic Dirac-Fock calculations and are widely accepted in the chemistry community. Our data matches the 2024 IUPAC provisional recommendations.

Valence electrons are those in the outermost principal energy level (n max) plus any incomplete (n-1)d or (n-2)f subshells for transition and inner transition metals. The tooltip provides additional detail for f‑block elements.
Scientific review: The configuration data and orbital filling rules implemented here have been cross-referenced with the CRC Handbook of Chemistry and Physics (104th edition), NIST ASD, and the Royal Society of Chemistry periodic table. Last update: June 2026.
References: IUPAC Periodic Table, WebElements, LibreTexts Chemistry, NIST ASD.