Theoretical studies have been made of the elastic scattering of low-energy light atoms from a perfect crystalline surface with a square unit cell with particular emphasis on selective adsorption. The atom–solid surface potential is approximated by a corrugated hard wall with attractive well, by a modulated square well with a smooth hard wall, by a Morse potential, and by a sum of Yukawa-6 pair potentials. It is found, independent of the model potential and without invoking inelastic processes, that the (0,1) selective adsorption results in minima in the specular and maxima in the (−1,1) diffraction intensity in agreement with recent experiments.