0_5287 When we downsize the matter to the sub-nanoscale, new fascinating physical and chemical properties may appear. Atomic nanoclusters provide a great example of this behavior, for which the size selection with single atom precision can showcase modifications of the properties even by adding or removing a single atom. These clusters represent indeed an unprecedented playground to look for new properties of matter, with applications appealing to many areas of materials science.By exploiting the combination of the ENAC (Exact number of atoms in each cluster) source and the synchrotron radiation produced by Elettra, and with the support of density functional theory calculations, we have investigated the process of oxidation of matter at the sub-nanoscale. A new world unfolded before our eyes, showing us that the properties of bulk and surface oxides cannot be easily extended to the nanoclusters.