A method for computing the chemisorption states of ionic lattices is presented in which the dominant interaction between the adsorbent and the adsorbate is a Madelung-type potential. The results describe quite well the chemisorption of oxygen on stable surfaces of ZnO and CdS. The same technique is used to establish a criterion for the stability of ionic surfaces. For the complete exposition, see J. Phys. Chem. Solids 29 (1968) 689.