Ion
Definition and meaning of Ion in chemistry.
Ion is an atom or group of covalently bonded atoms that carries a net electric charge because it has gained or lost one or more electrons relative to a neutral atom or molecule.
In more detail
An atom becomes an ion when the number of electrons no longer equals the number of protons. Losing electrons leaves an excess of positive charge, forming a cation; gaining electrons leaves an excess of negative charge, forming an anion. Ions form through processes like ionization (energy input strips or adds electrons), ionic bonding between metals and nonmetals, and dissociation of compounds in polar solvents such as water. Because they carry charge, ions conduct electricity in solution or when molten, and they are essential to ionic bonding, electrolyte balance in living cells, and acid-base chemistry.
Key facts
| Field | General Chemistry |
|---|---|
| Cation | Positively charged ion (electron loss), e.g. Na+ |
| Anion | Negatively charged ion (electron gain), e.g. Cl- |
| Polyatomic example | Sulfate ion, SO4^2- |
A sodium atom (Na) loses one electron to become the cation Na+, while a chlorine atom (Cl) gains that electron to become the anion Cl-. The electrostatic attraction between Na+ and Cl- forms the ionic compound sodium chloride (NaCl).
Frequently asked questions
What is the difference between a cation and an anion?
A cation is a positively charged ion formed when an atom or group of atoms loses one or more electrons; an anion is a negatively charged ion formed when electrons are gained. Cations are attracted to the cathode and anions to the anode during electrolysis, which is the origin of the names.
Are ions always single atoms?
No. Monatomic ions like Na+ come from single atoms, but polyatomic ions such as sulfate (SO4^2-) or ammonium (NH4+) are groups of covalently bonded atoms that together carry a net charge.