The versatile properties of bimetallic nanoparticles greatly expand the range of catalyzed chemical reactions. We demonstrate that surface chemistry can be understood and predicted using a simple adsorbate–surface interaction descriptor that relates charge polarization to chemical reactivity. Our density functional theory studies of O2 activation and CO oxidation catalyzed by Au7–Cu1 bimetallic nanoparticles supported on the TiO2(101) surface demonstrate that the generated oxidized Cu atom (CuO x ) can efficiently inhibit the aggregation of the active Cu sites. Moreover, because of the strong dipole–dipole interaction between the surface and the adsorbate on the oxidized Cu site, the adsorption of CO + O2/CO + O can be significantly enhanced, which can decrease the CO oxidation barriers and further improve catalytic performance. The product of the two electric dipole moments provides a parameter that allows us to predict the key catalytic properties for different adsorption sites and reaction pathways. The reported findings provide important insights into the mechanism of chemical reactivity of metallic clusters and generate a valuable principle for catalyst design.