anion ăn´ī˝ən [key], atom or group of atoms carrying a negative charge. The charge results because there are more electrons than protons in the anion. Anions can be formed from nonmetals by reduction (see oxidation and reduction ) or from neutral acids (see acids and bases ) or polar compounds by ionization. Anionic species include Cl , SO 4 −−, and CH 3COO . Highly colored intermediates in organic reactions are often radical anions (anions containing an unpaired electron). Salts are made up of anions and cations . See ion .

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