anion

/ˈænˌaɪɑn/

Other forms: anions

An anion is an atom that has more electrons than protons—in other words, an anion is an atom with a negative charge.

In a chemistry class, you'll come across the word ion frequently. That's an atom that either has extra electrons, giving it a negative charge, or is missing electrons, resulting in a positive charge. The negatively charged ions are called anions, and the positively charged ions are cations. In Greek, anion means "thing going up," which describes the movement anions make during the chemical process of electrolysis.

Definitions of anion

1. noun

   a negatively charged ion
   types:

   hydroxide ion, hydroxyl ion

   the anion OH having one oxygen and one hydrogen atom

   superoxide, superoxide anion

   the univalent anion O2-

   type of:

   ion

   a particle that is electrically charged (positive or negative); an atom or molecule or group that has lost or gained one or more electrons