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radical, in chemistry, group of atoms that are joined together in some particular spatial structure and that take part in most chemical reactions as a single unit. Important inorganic radicals include ammonium, NH4; carbonate, CO3 ; chlorate, ClO3, and perchlorate, ClO4 ; cyanide, CN; hydroxide, OH; nitrate, NO3; phosphate, PO4; silicate, SiO3 (meta) or SiO4 (ortho); and sulfate, SO4. The use of these radicals simplifies the naming and description of inorganic compounds, since such usage does not consider the electronic charge on the group. (When ions are dealt with, electronic charge must be considered.) In organic chemistry, the term radical is sometimes used synonymously with group; e.g., the group CH3 is sometimes called the methyl radical instead of the methyl group. This use is limited chiefly to alkyl groups and aryl groups; it is usually not applied to functional groups, such as carbonyl. Because the term radical easily could be taken to mean a free radical, the term group is preferred by some.
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