Activation of uranyl(V) oxo bonds in the gas phase is demonstrated by reaction of (UO2+)-O-16 with (H2O)-O-18 to produce (UOO+)-O-16-O-18 and (UO2+)-O-18. In contrast, neptunyl(V) and plutonyl(V) are comparatively inert toward exchange. Computed potential energy profiles (PEPs) reveal a lower yl oxo exchange transition state for uranyl(V)/water as compared with neptunyl(V)/water and plutonyl(V)/water. A correspondence between oxo exchange rates in gas phase and acid solutions is apparent; the contrasting oxo exchange rates of UO2+ and PuO2+ are considered in the context of covalent bonding in actinyls. Hydroxo exchange of (UO2)-O-16((OH)-O-16)(+) with (H2O)-O-18 to give (UO2)-O-16((OH)-O-18)(+) proceeded much faster than oxo exchange, in accord with a lower computed transition state for OH exchange. The PEP for the addition of H2O to UO2+ suggests that both UO2+center dot(H2O) and UO(OH)(2)(+) should be considered as potential products.