Electron configuration: definition in chemistry
Electron configuration: The arrangement of an atom's electrons in shells, subshells and orbitals, written as a list such as 1s² 2s² 2p⁶ for neon.
Each part of the notation gives the shell number, the subshell letter and, as a superscript, the number of electrons in that subshell. Electrons fill subshells in order of increasing energy, following the aufbau principle, the Pauli exclusion principle and Hund's rule. Long configurations are often shortened by writing the previous noble gas in brackets, so sodium becomes [Ne] 3s¹.
Examples
- Nitrogen — 1s² 2s² 2p³
- Chlorine — [Ne] 3s² 3p⁵
- Copper — [Ar] 3d¹⁰ 4s¹, an exception to the usual filling order
- Fe²⁺ — [Ar] 3d⁶, because iron loses its 4s electrons first
On the periodic table
You can read an element's electron configuration from its position: the period gives the outermost shell, and the block and column show which subshell is filling and how many electrons it holds.