Adsorption of pyridine and pyrrole on model iron oxide surfaces has been studied by X-ray photoelectron spectroscopy. At room temperature both molecules adsorb with their molecular identity intact. Upon heating above 320 K pyridine decomposes on the surface whereas pyrrole desorbs intact at 345 K. The bonding of pyridine and pyrrole to the surface at room temperature is studied by monitoring the change in measured N(1s) and C(1s) binding energies between gas-phase molecules and the monolayer phase at room temperature. The results suggest that pyridine bonds via electron donation from the non-bonding nitrogen lone pair to the surface while pyrrole bonds via electron donation from a π-bonding orbital to the surface. The differences in surface bonding are interpreted in the context of the concept of Lewis acids and bases applied to surfaces.