As an example of ionization, beta rays are fast electrons that lose energy as they pass through cells and interact with molecules.
Ionization differs from the ion formation that occurs in ordinary chemical reactions.
Sodium and chloride bind together because, separately, each atom is unstable. When the two atoms bind to form NaCl, sodium shares its single outer electron with chloride, and so, both are stable. In ordinary chemical reactions, such as the binding of Na to Cl, electrons that are lost or gained are always those on the outermost orbit. These charged atoms are called ions, and they are stable in water despite their electrical charges. What differs from an ordinary chemical reaction is that when radiation donates energy to atoms or molecules, electrons other than those on the most outer orbit can be released, which makes the atoms very unstable.