The mechanism of oxidation by hydrogen atoms of various acceptors is discussed. It is shown that two alternative pathways exist for the oxidation of ions dissolved in water. One involves the relatively slow reaction of H atoms with H+aq to form H2+aq, which oxidizes acceptors, e.g., I-aq. Alternatively other acceptors, e.g., metal cations may directly form intermediate complexes with H, with faster rate constants. The intermediate hydride complex may react with H+aq, yielding molecular hydrogen. When this faster, hydride complex, pathway is available, the slower H2+ mechanism may not be of kinetic importance. The experimental results for the oxidation of Fe2+ ions by H atoms can be adequately explained by this mechanism. The results of radiation chemical and photochemical experiments are discussed.