Radicals (often referred to as free radicals) are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative or zero charge. Even though they have unpaired electrons, by convention, metals and their ions or complexes with unpaired electrons are not radicals. [1] With some exceptions, the unpaired electrons cause radicals to be highly chemically reactive. Radicals are believed to be involved in degenerative diseases and cancers.