What is an Anion?

An ion is an atom or group of atoms, normally electrically neutral, that has lost or gained one or more electrons. The simplest ions are the proton (a hydrogen ion, H+, positive charge), and alpha particle (helium ion, He2+, consisting of two protons and two neutrons). An ion consisting of a single atom is called a monatomic ion, and an ion consisting of multiple atoms is called a polyatomic ion. Larger ions containing many atoms are called molecular ions. The process of converting electrically neutral atoms or molecules into ions and the state of being ionized is called ionization. The recombining of ions and electrons to form neutral atoms or molecules is called recombination.