Cambridge O Level Chemistry · Syllabus 5070 · 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 O Level Chemistry.
Questions students ask about Anion
How does an ionic bond form?
An ionic bond forms in two separate steps. First, outer electrons are transferred from a metal atom to a non-metal atom: the metal atom loses electrons to become a positive ion (a cation) and the non-metal atom gains them to become a negative ion (an anion). Second, the oppositely charged ions attract one another. The ionic bond is that strong electrostatic attraction between oppositely charged ions, not the transfer itself. Only electrons move; the nucleus and the proton number are untouched.