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Reference.org
Octet rule
open-in-new
<p>The octet rule is a <a href="/facts/Chemistry/SrNqkGVm">chemical</a> <a href="/facts/Rule_of_thumb/RopfGsJ0">rule of thumb</a> that reflects the theory that <a href="/facts/Main-group_element/2AG3QxJl">main-group elements</a> tend to <a href="/facts/Chemical_bond/ArNUMnIB">bond</a> in such a way that each <a href="/facts/Atom/69syB8dH">atom</a> has eight <a href="/facts/Electrons/L0KBo5cW">electrons</a> in its <a href="/facts/Valence_shell/mXPA15VP">valence shell</a>, giving it the same <a href="/facts/Electron_configuration/TQjRr22P">electronic configuration</a> as a <a href="/facts/Noble_gas/j0yHMEAE">noble gas</a>. The rule is especially applicable to <a href="/facts/Carbon/ukrgQexo">carbon</a>, <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a>, <a href="/facts/Oxygen/acyn6o8r">oxygen</a>, and the <a href="/facts/Halogens/YeFgWHeA">halogens</a>; although more generally the rule is applicable for the <a href="/facts/S-block/BbzD5jUU">s-block</a> and <a href="/facts/P-block/BbzD5jUU">p-block</a> of the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a>. Other rules exist for other elements, such as the <a href="/facts/Duplet_rule/X9jxSsos">duplet rule</a> for <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> and <a href="/facts/Helium/yRul93TG">helium</a>, and the <a href="/facts/18-electron_rule/KNfG6tpM">18-electron rule</a> for <a href="/facts/Transition_metal/0slGWoLQ">transition metals</a>. </p><p>The valence electrons in molecules like carbon dioxide (CO₂) can be visualized using a <a href="/facts/Lewis_structure/PTgB3gtW">Lewis electron dot diagram</a>. In <a href="/facts/Covalent_bond/EzMLf3Pz">covalent bonds</a>, electrons shared between two atoms are counted toward the octet of both atoms. In carbon dioxide each oxygen shares four electrons with the central carbon, two (shown in red) from the oxygen itself and two (shown in black) from the carbon. All four of these electrons are counted in both the carbon octet and the oxygen octet, so that both atoms are considered to obey the octet rule. </p>