Valence electron

In <a href="/facts/Chemistry/SrNqkGVm">chemistry</a> and <a href="/facts/Physics/a7aH2y08">physics</a>, valence electrons are <a href="/facts/Electrons/L0KBo5cW">electrons</a> in the outermost <a href="/facts/Electron_shell/QxI30eh9">shell</a> of an <a href="/facts/Atom/FoQ4kGN5">atom</a>, and that can participate in the formation of a <a href="/facts/Chemical_bond/ArNUMnIB">chemical bond</a> if the outermost shell is not <a href="/facts/Closed_shell/TQjRr22P">closed</a>. In a single <a href="/facts/Covalent_bond/EzMLf3Pz">covalent bond</a>, a shared pair forms with both atoms in the bond each contributing one valence electron.
The presence of valence electrons can determine the <a href="/facts/Chemical_element/0jducgWD">element</a>'s <a href="/facts/Chemistry/SrNqkGVm">chemical</a> properties, such as its <a href="/facts/Valence_(chemistry)/ck7cHByj">valence</a>—whether it may bond with other elements and, if so, how readily and with how many. In this way, a given element's <a href="/facts/Reactivity_(chemistry)/PuJ2pmRT">reactivity</a> is highly dependent upon its <a href="/facts/Electron_configuration/TQjRr22P">electronic configuration</a>. For a <a href="/facts/Main-group_element/2AG3QxJl">main-group element</a>, a valence electron can exist only in the outermost <a href="/facts/Electron_shell/QxI30eh9">electron shell</a>; for a <a href="/facts/Transition_metal/0slGWoLQ">transition metal</a>, a valence electron can also be in an inner shell.
An atom with a closed shell of valence electrons (corresponding to a <a href="/facts/Noble_gas_configuration/TQjRr22P">noble gas configuration</a>) tends to be <a href="/facts/Inert_gases/3EkBEoYh">chemically inert</a>. Atoms with one or two valence electrons more than a closed shell are highly reactive due to the relatively <a href="/facts/Ionization_energy/lezUajfA">low energy</a> to remove the extra valence electrons to form a positive <a href="/facts/Ion/3bePpDna">ion</a>. An atom with one or two electrons fewer than a closed shell is reactive due to its tendency either to gain the missing valence electrons and form a negative ion, or else to share valence electrons and form a covalent bond.
Similar to a <a href="/facts/Core_electron/LQuGLKcG">core electron</a>, a valence electron has the ability to absorb or release energy in the form of a <a href="/facts/Photon/mFNhAEzA">photon</a>. An energy gain can trigger the electron to move (jump) to an outer shell; this is known as <a href="/facts/Excited_state/czcLYNnr">atomic excitation</a>. Or the electron can even break free from its associated atom's shell; this is <a href="/facts/Ionization/W13Ceavd">ionization</a> to form a positive ion. When an electron loses energy (thereby causing a photon to be emitted), then it can move to an inner shell which is not fully occupied.

Valence electron open-in-new

Valence electron