Ion

An electrostatic potential map of the nitrate ion (NO3⁻). Areas colored red are lower in energy than areas colored yellow

An ion is an atom or molecule that possesses a number of electrons that is greater or lower than the number of protons, yielding a net electric charge.

An ion with a positive ( + ) charge is called a cation. An ion with a negative ( - ) charge is called an anion. An ion with both a positive and negative charge is a zwitterion.