Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Electron counting
open-in-new
<p>In <a href="/facts/Chemistry/SrNqkGVm">chemistry</a>, electron counting is a formalism for assigning a number of <a href="/facts/Valence_electrons/mXPA15VP">valence electrons</a> to individual atoms in a molecule. It is used for classifying compounds and for explaining or predicting their electronic structure and <a href="/facts/Chemical_bond/ArNUMnIB">bonding</a>. Many rules in chemistry rely on electron-counting: </p> <ul><li><a href="/facts/Octet_rule/X9jxSsos">Octet rule</a> is used with <a href="/facts/Lewis_structure/PTgB3gtW">Lewis structures</a> for <a href="/facts/Main_group_element/2AG3QxJl">main group elements</a>, especially the lighter ones such as <a href="/facts/Carbon/ukrgQexo">carbon</a>, <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a>, and <a href="/facts/Oxygen/acyn6o8r">oxygen</a>,</li> <li><a href="/facts/18-electron_rule/KNfG6tpM">18-electron rule</a> in <a href="/facts/Inorganic_chemistry/ErD6ypnb">inorganic chemistry</a> and <a href="/facts/Organometallic_chemistry/bhqFz2P0">organometallic chemistry</a> of <a href="/facts/Transition_metal/0slGWoLQ">transition metals</a>,</li> <li><a href="/facts/H%25C3%25BCckel%2527s_rule/5BDPHGnk">Hückel's rule</a> for the <a href="/facts/Pi_electron/3Q6LAGYK">π-electrons</a> of <a href="/facts/Aromaticity/wK0DzRY6">aromatic compounds</a>,</li> <li><a href="/facts/Polyhedral_skeletal_electron_pair_theory/hnVKFea2">Polyhedral skeletal electron pair theory</a> for <a href="/facts/Polyhedron/UC0p9FTF">polyhedral</a> <a href="/facts/Cluster_compound/EsuLgxJU">cluster compounds</a>, including transition metals and main group elements and mixtures thereof, such as <a href="/facts/Boranes/wu3RTzUS">boranes</a>.</li></ul> <p>Atoms are called "<a href="/facts/Electron_deficiency/3fBwxBBH">electron-deficient</a>" when they have too few electrons as compared to their respective rules, or "<a href="/facts/Hypervalent_molecule/goPjlm9W">hypervalent</a>" when they have too many electrons. Since these compounds tend to be more reactive than compounds that obey their rule, electron counting is an important tool for identifying the reactivity of molecules. While the counting formalism considers each atom separately, these individual atoms (with their hypothetical assigned charge) do not generally exist as free <a href="/facts/Chemical_species/A8BxM3oW">species</a>. </p>