An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons , giving it a net positive or negative electrical charge . The name was given by physicist Michael Faraday for the substances that allow a current to pass ("go") between electrodes in a solution, when an electric field is applied. It is from Greek ιον , meaning "going". An ion consisting of a single atom is an atomic or monatomic ion ; if it consists of two or more atoms, it is a molecular or polyatomic ion . Contents [ hide ] 1 Anions and cations 2 General 2.1 History and discovery 2.2 Characteristics 2.3 Natural occurrences 2.3.1 Astronomical 2.4 Related technology 3 Chemistry 3.1 Notation 3.1.1 Denoting the charged state 3.1.2 Su...