After reading this section you will be able to:

  • Describe what ions are.
  • Explain the process of ionization.


An ion is an atom, group of atoms, or a particle with a positive or negative charge. Ionization is any process that changes the electrical balance within an atom. If we remove an electron from a stable atom, the atom becomes electrically incomplete/unbalanced. That is, there are more protons in the nucleus (positive charges) than there are electrons (negative charges). With an electron removed, the atom possesses a plus one charge, therefore it is a positive ion. Consequently, the liberated electron is a negative ion, as long as it exists by itself and does not combine with another atom. One way ionization occurs is through radiation. 

 A proton is the same as Hydrogen +1 because this is a hydrogen atom that is missing an electron. An electron can be called Hydrogen -1 because it is a hydrogen atom that is missing a proton. A helium atom that is missing a proton is called helium -1. A helium atom that is missing an electron is called helium +1. A beryllium atom that is missing two electrons is called beryllium +2.

Atoms are held together by a binding energy. This means that the electrons are held in their electron shells by a quantity of binding energy. In order to liberate an electron from its parent atom, it will take energy that is at least equal to the binding energy that holds the electron.

The amount of ionization that occurs is dependent upon two main factors, (1) the radiation energy, and (2) the type of material the radiation is interacting with. The process of ionization will be discussed more in depth in the X-rays module.


  1. Ions have a positive or negative charge.
  2. This process of creating ions is called ionization.
  3. Radiation can cause ionization.