Ion See also: Acids And Bases; Electrolyte Atom, or group of atoms, having a net electric charge, acquired by gaining or losing one or more Electrons or Protons. A simple ion consists of only one Charged atom; a complex ion consists of an aggregate of atoms with a net charge. Because the electron and proton have equal but opposite unit charges, the charge of an ion is always expressed as a whole number of positive or negative unit charges. If an atom or group loses electrons or gains protons, it will have a net positive charge and is called a cation. If an atom or group gains electrons or loses protons, it will have a net negative charge and is called an anion.