An electrically neutral atom becomes an ion through the removal or addition of electrons. A negatively charged ion is called an anion and a positively charged ion is a cation. There are a variety of ways in which atoms can be ionized. Chemical reactions, heat, collision between particles, and radiation (such as X-rays and gamma rays) can alter the structure of an atom.

Ion can be manipulated by magnetic and electric fields, which affect their movement in different ways. Electricity causes ions to flow along the electric field. However, magnetism causes ions to spiral along the magnetic field lines. The aurora borealis and aurora australis (northern and southern lights) are caused by the sun's ions, which spiral along the lines of the earth's magnetic field causing the atmosphere to glow.

The study of ions began with Humphry Davy and his assistant Michael Faraday. Davy...