A model is proposed to explain the reduction in work function of an Na‐covered W (112) surface by oxygen adsorption. It is proposed that oxygen atoms are adsorbed directly to the W (112) substrate, forcing the Na atoms to the second layer. Since the dipole moment of an O&sngbnd;Na bond is much larger than that of a W&sngbnd;Na bond, it is believed that the W&sngbnd;O&sngbnd;Na bonding has larger dipole moment than that of the W&sngbnd;Na bond thus causing a decrease in work function. LEED results consistent with the proposed model is presented.