Electron Configuration
The notation describing how an atom's electrons are distributed among its available orbitals.
Formula / equation
1s² 2s² 2p⁶ …
Unit
Dimensionless
In depth
Configurations are built by filling orbitals in order of increasing energy while respecting the Pauli principle and Hund's rule. Condensed notation replaces filled inner shells with the preceding noble gas. Half-filled and fully filled subshells confer extra stability, causing the well-known anomalies at chromium and copper.
Examples in the real world
Oxygen is 1s² 2s² 2p⁴; copper is [Ar] 3d¹⁰ 4s¹ rather than the predicted 3d⁹ 4s².