The electron configuration of an atom describes how its electrons are arranged in atomic orbitals, following the Aufbau principle, Pauli exclusion principle, and Hund's rule. This calculator shows the full configuration, noble gas shorthand, and ion configurations for all 118 elements — useful for chemistry, physics, and materials science coursework.
Element Input
Result
How to Use the Electron Configuration Calculator
Electron configurations describe how an atom's electrons fill atomic orbitals. This calculator applies the Aufbau principle (fill lowest energy orbitals first), the Pauli exclusion principle (max 2 electrons per orbital with opposite spins), and Hund's rule (maximize unpaired electrons in a subshell) to generate correct configurations for any element.
Example: Iron (Fe, Z=26)
Type "Fe", "Iron", or "26" in the search box and click Calculate. The full configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s². The noble gas shorthand is [Ar] 3d⁶ 4s², where [Ar] represents the 18 core electrons of Argon. Iron is in the d-block, period 4, group 8 with 8 valence electrons (counting 4s² + 3d⁶). Its 4 unpaired electrons in the 3d subshell make it paramagnetic.
Calculating Ion Configurations
For Fe²⁺ (iron losing 2 electrons), enter "Fe" and "+2" in the ion charge field. Electrons are removed from the highest principal quantum number first — the 4s² electrons are removed before 3d electrons, giving [Ar] 3d⁶ for Fe²⁺. For Fe³⁺, three electrons are removed: both 4s electrons plus one 3d electron, giving [Ar] 3d⁵. For anions (negative charge), electrons are added to the next available orbital following Aufbau order.
Special Cases: Chromium and Copper
Chromium (Cr, Z=24) has the configuration [Ar] 3d⁵ 4s¹ instead of the expected [Ar] 3d⁴ 4s². A half-filled d subshell (3d⁵ with 5 unpaired electrons) is particularly stable. Similarly, Copper (Cu, Z=29) is [Ar] 3d¹⁰ 4s¹ instead of [Ar] 3d⁹ 4s² because a completely filled d subshell (3d¹⁰) provides extra stability. This calculator uses the actual observed configurations from experimental data.
Valence Electrons and Reactivity
Valence electrons determine chemical reactivity. Main group elements follow the octet rule — they react to achieve 8 valence electrons (like noble gases). Sodium (Na) has 1 valence electron and readily loses it to form Na⁺. Chlorine (Cl) has 7 valence electrons and readily gains one to form Cl⁻. Transition metals have more complex reactivity because both s and d electrons can participate in bonding.
For a detailed walkthrough, see our guide: Electron Configuration Guide.
FAQ
What is an electron configuration?
An electron configuration describes how electrons are distributed among atomic orbitals in an atom. It follows the notation 1s² 2s² 2p⁶... where the number is the principal quantum number, the letter is the subshell (s, p, d, f), and the superscript is the number of electrons in that subshell.
What is the noble gas shorthand notation?
The noble gas shorthand replaces the inner-shell (core) electrons with the symbol of the preceding noble gas in brackets. For example, Iron (Fe) is [Ar] 3d⁶ 4s² — the [Ar] represents Argon's 18 electrons, leaving only the 8 valence electrons visible. This makes it easier to see which electrons participate in bonding.
How do I calculate electron configurations for ions?
For cations (positive ions), remove electrons from the highest principal quantum number subshells first. For Fe²⁺, remove 2 electrons from 4s to get [Ar] 3d⁶. For anions (negative ions), add electrons to the next available orbital following Aufbau order.
Why do some elements have unexpected electron configurations?
Chromium (Cr) is [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s² because a half-filled d subshell (3d⁵) is extra stable. Similarly, Copper (Cu) is [Ar] 3d¹⁰ 4s¹ instead of [Ar] 3d⁹ 4s² because a fully filled d subshell (3d¹⁰) provides extra stability.
What does paramagnetic vs diamagnetic mean?
Paramagnetic atoms have one or more unpaired electrons and are weakly attracted to magnetic fields. Diamagnetic atoms have all electrons paired and are weakly repelled by magnetic fields. Iron (Fe) with 4 unpaired electrons is strongly paramagnetic; Zinc (Zn) with all electrons paired is diamagnetic.
How many valence electrons does an element have?
Valence electrons are the electrons in the outermost principal quantum number shell. For main group elements (s and p blocks), valence electrons equal the group number. For transition metals, valence electrons include both the outer s electrons and the d electrons in the same or next-to-last shell.
Is this electron configuration tool free?
Yes, completely free. No account or signup required. All data runs locally in your browser.