Electron counting

Electron counting is the systematic tally of valence electrons in atoms, molecules, or coordination complexes. The total helps predict bonding, charge, and chemical stability.

Lewis structure: A diagram showing valence electrons as bonds and lone pairs around atoms. Lewis structures make electron pairs explicit for counting in covalent molecules.
Valence electron: An electron in an atom’s outer shell that can participate in chemical bonding. Electron counting begins by identifying which electrons can enter bonds.
Organometallic chemistry: The study of compounds containing bonds between carbon atoms and metals. Electron counting is a routine tool for analyzing organometallic structures and reactions.
Ionic counting method: A coordination-complex convention that assigns ligands formal charges before counting metal and ligand electrons. It is the principal alternative to the neutral-fragment counting convention.
Formal charge: An atom’s assigned charge when bonding electrons are divided equally between bonded atoms. Formal charges check whether a proposed Lewis structure distributes electrons consistently.
Covalent bond: A chemical bond formed when atoms share one or more pairs of electrons. Shared electron pairs must be assigned according to the chosen counting convention.
Metal carbonyl: A coordination compound containing carbon monoxide ligands bonded to a metal. Carbonyl complexes provide classic examples of electron counts predicting stability.
Covalent counting method: A coordination-complex convention that counts neutral ligand fragments and metal group electrons. It describes the neutral approach to assigning electrons in complexes.
Oxidation state: A bookkeeping charge assigned to an atom by treating bonds as fully ionic. Oxidation states support ionic electron counts for transition-metal complexes.
Coordination complex: A compound containing a central metal atom or ion bonded to surrounding ligands. Metal complexes are a major setting for systematic electron-counting rules.

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AntiaromaticityRelated: The 4n criterion depends on counting the ring's participating π electrons.