Surface plasticity and fracture in metals are intimately influenced by exposure to specific chemical species, with important consequences for manufacturing processes and environment assisted cracking (EAC). These fracture phenomena are impossible to explain purely using adsorbate-induced changes in surface energy. In this seminar I will present a unique embrittlement effect in Al that is instead mediated by surface stress, induced by an adsorbed organic monolayer. Atomistic simulations show that the adsorbate carbon-chain length lc controls the surface stress via van der Waals forces, being compressive for lc 8 and tensile otherwise. For lc > 8, we demonstrate experimentally that the nanoscale film causes a ductile-to-brittle transition on the macroscale. Concomitant with this transition is a nearly 85% reduction in deformation forces. Additional simulations reveal that the microscopic mechanism for the embrittlement is via suppression of dislocation emission at incipient crack-tips. In addition to challenging long-held views on environment-assisted fracture, these results pertaining to surface-stress induced embrittlement suggest profitable utility in manufacturing processes such as machining and comminution.