Electron Configuration Calculator

Calculate electron configuration for any element or ion. See orbital diagrams, noble gas notation, and quantum numbers with step-by-step explanations.

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Electron Configuration Results

Select an element or enter atomic number to calculate electron configuration

What is Electron Configuration

Electron configuration tells you how electrons are arranged around an atom's nucleus. Think of it as the address system for electrons—they occupy specific energy levels and orbitals, following rules that keep the atom stable.

Every element has a unique electron configuration. Sodium has 11 electrons, and they fill up orbitals in a specific order: first the 1s orbital holds 2, then 2s holds 2, 2p holds 6, and the last electron sits in 3s. We write this as 1s² 2s² 2p⁶ 3s¹, or more simply as [Ne] 3s¹ using the noble gas shorthand.

Why does this matter? The outermost electrons—called valence electrons—determine how an element behaves in chemical reactions. Elements in the same column of the periodic table have similar configurations and similar chemistry. That's why sodium and potassium both react vigorously with water.

Key Formulas for Electron Configuration

Aufbau Principle (n + l Rule):

Electrons fill orbitals in order of increasing (n + l) value

Lower n fills first when (n + l) values are equal

Subshell Electron Capacity:

Maximum Electrons = 2(2l + 1)

Where l = 0 (s), 1 (p), 2 (d), 3 (f)

Total Electrons for Ions:

e⁻ = Z - charge (cation) or Z + |charge| (anion)

Some elements break the expected pattern. Chromium should be [Ar] 4s² 3d⁴, but it's actually [Ar] 4s¹ 3d⁵. Copper should be [Ar] 4s² 3d⁹, but it's [Ar] 4s¹ 3d¹⁰. These exceptions happen because half-filled and fully-filled d subshells are more stable. The calculator automatically handles these special cases.

Electron Configuration Reference Table

Element Symbol Z Full Configuration Noble Gas Form
HydrogenH11s¹1s¹
HeliumHe21s²1s²
LithiumLi31s² 2s¹[He] 2s¹
CarbonC61s² 2s² 2p²[He] 2s² 2p²
NitrogenN71s² 2s² 2p³[He] 2s² 2p³
OxygenO81s² 2s² 2p⁴[He] 2s² 2p⁴
NeonNe101s² 2s² 2p⁶[He] 2s² 2p⁶
SodiumNa111s² 2s² 2p⁶ 3s¹[Ne] 3s¹
MagnesiumMg121s² 2s² 2p⁶ 3s²[Ne] 3s²
AluminumAl131s² 2s² 2p⁶ 3s² 3p¹[Ne] 3s² 3p¹
PhosphorusP151s² 2s² 2p⁶ 3s² 3p³[Ne] 3s² 3p³
SulfurS161s² 2s² 2p⁶ 3s² 3p⁴[Ne] 3s² 3p⁴
ChlorineCl171s² 2s² 2p⁶ 3s² 3p⁵[Ne] 3s² 3p⁵
ArgonAr181s² 2s² 2p⁶ 3s² 3p⁶[Ne] 3s² 3p⁶
PotassiumK191s² 2s² 2p⁶ 3s² 3p⁶ 4s¹[Ar] 4s¹
CalciumCa201s² 2s² 2p⁶ 3s² 3p⁶ 4s²[Ar] 4s²
Chromium *Cr241s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵[Ar] 4s¹ 3d⁵
IronFe261s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶[Ar] 4s² 3d⁶
CobaltCo271s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷[Ar] 4s² 3d⁷
NickelNi281s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸[Ar] 4s² 3d⁸
Copper *Cu291s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰[Ar] 4s¹ 3d¹⁰
ZincZn301s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰[Ar] 4s² 3d¹⁰
BromineBr35...4s² 3d¹⁰ 4p⁵[Ar] 4s² 3d¹⁰ 4p⁵
KryptonKr36...4s² 3d¹⁰ 4p⁶[Ar] 4s² 3d¹⁰ 4p⁶

* Exception elements where half-filled or full d-subshell provides extra stability

For ions, electron configuration changes based on charge. A chloride ion (Cl⁻) has gained one electron, so its configuration becomes [Ar]. An iron(II) ion (Fe²⁺) loses its 4s electrons first, not the 3d electrons—this is a common misconception. The calculator handles these ion configurations automatically.