Editing Electron configuration (section)

{{Short description|Mode of arrangement of electrons in different shells of an atom}}
[[File:Electron orbitals.svg|right|thumb|upright=1.5|[[Electron]] [[Atomic orbital|atomic]] and [[molecular orbital]]s]]
[[File:Electron shell 003 Lithium - no label.svg|thumb|120px|A [[Bohr model|Bohr diagram]] of [[lithium]]]]

In [[atomic physics]] and [[quantum chemistry]], the '''electron configuration''' is the [[Distribution (mathematics)|distribution]] of [[electron]]s of an [[atom]] or [[molecule]] (or other physical structure) in [[Atomic orbital|atomic]] or [[molecular orbital]]s.<ref name="IUPAC1">{{GoldBookRef|file=C01248|title=configuration (electronic)}}</ref> For example, the electron configuration of the [[neon]] atom is {{nowrap|1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>6</sup>}}, meaning that the 1s, 2s, and 2p [[Electron shell#Subshells|subshells]] are occupied by two, two, and six electrons, respectively.

Electronic configurations describe each electron as moving independently in an [[Atomic orbital|orbital]], in an average [[Field (physics)|field]] created by the [[Atomic nucleus|nuclei]] and all the other electrons. Mathematically, configurations are described by [[Slater determinants]] or [[configuration state function]]s.

According to the laws of [[Introduction to quantum mechanics|quantum mechanics]], a [[Energy level|level of energy]] is associated with each electron configuration. In certain conditions, electrons are able to move from one configuration to another by the emission or absorption of a [[quantum]] of energy, in the form of a [[photon]].

Knowledge of the electron configuration of different atoms is useful in understanding the structure of the [[periodic table|periodic table of elements]], for describing the [[chemical bond]]s that hold atoms together, and in understanding the [[chemical formula]]s of compounds and the [[Molecular geometry|geometries of molecules]]. In bulk materials, this same idea helps explain the peculiar properties of [[lasers]] and [[semiconductors]].