Ion

An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. An ion consisting of a single atom is called a monatomic ion, and an ion consisting a negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion (; an-eye-on) due to its attraction to anodes. A positively-charged ion, which has fewer electrons than protons, is known as a cation (; cat-eye-on) due to its attraction to cathodes. A polyatomic anion that contains oxygen is sometimes known as an oxyanion.