Britannica Sources used in this answer

How do ions form during chemical reactions?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Bohr model diagram of a hydrogen atom showing a green nucleus labeled H, a single electron orbit, and text with atomic mass 1.008 and electron configuration 1. — atom The Bohr model describes the structure of atoms, in this case hydrogen.

Ions are formed when electrically neutral atoms or molecules gain or lose electrons, a process known as ionization. During chemical reactions, this typically occurs through the following mechanisms:

Electron Transfer: In ionic bonding, electrons are transferred from one atom to another. Generally, metals (which have few valence electrons) lose electrons to become positively charged cations, while nonmetals (which have more valence electrons) gain those electrons to become negatively charged anions.12
Bond Rupture: Ions can form when a covalent bond between two atoms breaks in such a way that both bonding electrons remain with one of the atoms.1
Chemical Interaction: Ions may also form through the combination of existing ions with other particles, such as when a hydrogen cation reacts with an ammonia molecule.1

Once formed, these oppositely charged ions are held together by electrostatic forces, often creating stable, crystalline structures.134