When atoms or molecules are adsorbed on a surface, two phenomena can lead to a change in the surface stress. One is a change in the electron density of the atoms in the surface, which changes the in-plane bonding and thus the surface stress. A second is due to interactions between the adsorbed atoms or molecules themselves, which may want to be further apart (or closer) than is possible with the atomic spacings in the surface. Note that since adsorption often depends strongly upon the environment, for instance gas pressure and temperature, the surface stress tensor will show a similar dependence.