Monatomic Ion Definition and Examples

Learn What a Monatomic Ion Is in Chemistry

Sodium chloride dissociates into monatomic sodium and chloride ions in water.
Sodium chloride dissociates into monatomic sodium and chloride ions in water. LAGUNA DESIGN / Getty Images

A monatomic ion is an ion formed from a single atom. In other words, it is a single atom that has a different number of protons and electrons. The charge on the ion is the difference between the number of protons and electrons. If there are more protons, the charge is positive. If there is an excess of electrons, the charge is negative. Metals typically form cations, while nonmetals usually form anions.

Examples

KCl dissociates in water into K+ and Cl- ions. Both of these ions are monatomic ions. Ionization of an oxygen atom may result in O2-, which is a monatomic ion. Hydrogen usually forms the monatomic ion H+, however, it sometimes acts as an anion and forms H-.

Monatomic Ion Versus Monatomic Atom

Technically, a monatomic ion is a form of monatomic atom. However, the term "monatomic atom" usually refers to neutral atoms of elements. Examples include atoms of krypton (Kr) and neon (Ne). While krypton, neon, and other noble gases typically exist as monatomic atoms, they rarely form ions.

Source

  • William Masterton; Cecile Hurley (2008). Chemistry: Principles and Reactions. Cengage Learning. p. 176. ISBN 0-495-12671-3.