The chemisorption of a series of diatomic molecules on the Si(100) surface was investigated using scanning tunneling microscopy, STM. For the molecules studied, dissociative chemisorption occurs and the adatoms produced are found at two types of surface sites. The stability of these sites is studied by exciting the adsorbate system via a tip voltage pulse. As a result of this excitation the adatoms undergo a rearrangement that depends both on the nature of the adspecies and on the site being stimulated. The directionality and spatial extent of these rearrangements are also site dependent. This behavior is attributed to the presence of anisotropic site-dependent repulsive interactions on the Si(100) surface.