Radical (chemistry)

The term radical can have two distinct meanings in chemistry. The first is that a radical is an atom or molecule with free unpaired electrons. This causes them to be highly reactive as they try to bond these electrons with other atoms. In this sense, a radical is no different from a free radical. In the other sense, a radical is a collection of atoms that act as a common entity in reaction. For example, the ammonium ion, NH₄⁺, is a radical in that it can react as a single entity:

NH₄OH + NaHSO₄ → Na(NH₄)SO₄ + H₂O

Radicals in this second sense are often enclosed in parentheses in the expressions of chemical formulas (in this case the radical is the trivalent phosphate anion, PO₄^3-):

Fe₃(PO₄)₂

Radicals, depending on whether they are largely ionic or covalent in character, may also be referred to as a polyatomic ion or a functional group. A radical, such as ferrocyanide[?], with a central metal atom and dominated by coordination chemistry with ligands, would be called a complex ion.