Cation: definition in chemistry
Cation: A positively charged ion, formed when an atom or group of atoms loses one or more electrons.
Because it has fewer electrons than protons, a cation carries a positive charge, and a simple cation is smaller than the atom it came from. Metals form cations easily because they hold their outer electrons loosely. During electrolysis, cations move toward the negative electrode, the cathode, which is where their name comes from.
Examples
- Na⁺ — sodium ion
- Mg²⁺ — magnesium ion
- Fe³⁺ — iron(III) ion, found in rust
- H₃O⁺ — hydronium ion, present in every acidic water solution
On the periodic table
Metals on the left side and in the middle of the table form cations, and in groups 1, 2 and 13 the charge usually matches the number of valence electrons: +1, +2 and +3.