a charged particle. This umbrella term can refer to a positively-charged particle (cation) or a negatively-charged particle (anion). The charge comes from having an unequal number of protons (+) & electrons (-) and can be associated with a single atom (such as Na⁺ or Cl⁻) or a larger molecule (polyatomic ions such as PO₄³⁻). The “# of charges” is referred to as the valency. So, for example, Na⁺ is monovalent and Ca²⁺ is divalent. Negatively-charged ions are attracted to one another and can form strong non-covalent bonds called “ionic bonds” or “salt bridges.” The neutral combo of an anion + a cation is called a salt.