Cambridge IGCSE Chemistry · Syllabus 0620 · Atoms, Elements and Compounds
Anion
What is Anion?
A negatively charged ion, formed when an atom gains one or more electrons. Non-metal atoms commonly form anions by gaining enough electrons to complete their outer shell. The nucleus is unchanged, so the element is unchanged; the negative charge arises because there are now more electrons than protons.
This definition is part of the Atoms, Elements and Compounds chapter in Cambridge IGCSE Chemistry.