Cation

A cation is an atom or molecule with a net positive electrical charge, usually because it has lost one or more electrons.

Ionization energy: The energy required to remove an electron from an atom or ion in the gas phase. It quantifies the energy cost of forming a cation by removing an electron.
Ion: An atom or molecule with a net electrical charge because its numbers of protons and electrons differ. Cations are the positively charged members of the broader ion family.
Sodium–potassium pump: A membrane protein that uses ATP to move sodium ions out of cells and potassium ions into them. It maintains unequal concentrations of two major cations across cell membranes.
Monatomic ion: An ion consisting of a single atom with a net electrical charge. Many familiar cations, including sodium and calcium ions, are monatomic.
Electron configuration: The arrangement of electrons among an atom’s or ion’s energy levels and orbitals. Electron configurations change when atoms lose electrons to become cations.
Anion: An atom or molecule with a net negative electrical charge, usually because it has gained electrons. Anions contrast with cations in both charge sign and typical electron transfer.
Action potential: A rapid, temporary change in a cell’s membrane voltage that propagates along excitable cells. Sodium and potassium cation movements generate and reset many action potentials.
Polyatomic ion: A charged group of two or more covalently bonded atoms that behaves as a unit. Polyatomic cations such as ammonium carry positive charge without being single atoms.
Oxidation state: A bookkeeping value representing an atom’s apparent charge in a compound under specified rules. Electron loss that forms cations often corresponds to an increase in oxidation state.
Electric charge: A fundamental property of matter that determines its electromagnetic interactions. A cation’s defining feature is its positive net electric charge.

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