Understanding the mechanical behavior of nanoparticles has become a key factor for the success of many engineering applications. Classically, for polycrystalline materials one would expect an increase in the yield strength for smaller grain sizes according to the empirical Hall-Petch equation. However, at the nanoscale, this mechanism seems to break down. Despite the number of interesting papers published on this topic, controversy persists and consensus is still lacking. While this discussion is of great interest for polycrystalline nanoparticles, contemporary models for strengthening are inappropriate for single-crystal nanoparticles, which, altogether, pose a very different problem: the absence of grain boundaries to inhibit dislocations. In this context, we present a new model wherein the change in Gibbs Free Energy of an edge dislocation in a single-crystal particle provides a driving force for dislocation motion. These results show that dislocations become unstable and are spontaneously ejected from the particles below a certain critical size.