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 for anions
From The Collaborative International Dictionary of English v.0.48 :

  Ion \I"on\ ([imac]"[o^]n), n. [Gr. 'io`n, neut, of 'iw`n, p. pr.
     of 'ie`nai to go.]
     1. (Elec. Chem.) an atom or goup of atoms (radical) carrying
        an electrical charge. It is contrasted with neutral atoms
        or molecules, and free radicals. Certain compounds, such
        as sodium chloride, are composed of complementary ions in
        the solid (crystalline) as well as in solution. Others,
        notably acids such as hydrogen chloride, may occur as
        neutral molecules in the pure liquid or gas forms, and
        ionize almost completely in dilute aqueous solutions. In
        solutions (as in water) ions are frequently bound
        non-covalently with the molecules of solvent, and in that
        case are said to be solvated. According to the
        electrolytic dissociation theory, the molecules of
        electrolytes are divided into ions by water and other
        solvents. An ion consists of one or more atoms and carries
        one unit charges of electricity, 3.4 x 10^{-10
        electrostatic units, or a multiple of this. Those which
        are positively electrified (hydrogen and the metals) are
        called cations; negative ions (hydroxyl and acidic atoms
        or groups) are called anions.
     Note: Thus, hydrochloric acid ({HCl) dissociates, in aqueous
           solution, into the hydrogen ion, H+, and the chlorine
           ion, Cl-; ferric nitrate, Fe(NO3)3, yields the
           ferric ion, Fe+++, and nitrate ions, NO3-, NO3-,
           NO3-. When a solution containing ions is made part of
           an electric circuit, the cations move toward the
           cathode, the anions toward the anode. This movement is
           called migration, and the velocity of it differs for
           different kinds of ions. If the electromotive force is
           sufficient, electrolysis ensues: cations give up their
           charge at the cathode and separate in metallic form or
           decompose water, forming hydrogen and alkali;
           similarly, at the anode the element of the anion
           separates, or the metal of the anode is dissolved, or
           decomposition occurs. Aluminum and chlorine are
           elements prepared predominantly by such electrolysis,
           and depends on dissolving compounds in a solvent where
           the element forms ions. Electrolysis is also used in
           refining other metals, such as copper and silver. Cf.
           Anion, Cation.
           [Webster 1913 Suppl.]
     2. One of the small electrified particles into which the
        molecules of a gas are broken up under the action of the
        electric current, of ultraviolet and certain other rays,
        and of high temperatures. To the properties and behavior
        of ions the phenomena of the electric discharge through
        rarefied gases and many other important effects are
        ascribed. At low pressures the negative ions appear to be
        electrons; the positive ions, atoms minus an electron. At
        ordinary pressures each ion seems to include also a number
        of attached molecules. Ions may be formed in a gas in
        various ways.
        [Webster 1913 Suppl.]

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