A method to estimate the differences in binding energy among surface atoms at crystallographically different sites is presented. Single Si adatoms can be extracted from the Si(111)7×7 surface using a scanning tunneling microscope (STM). In such experiments, center Si adatoms are extracted with a larger probability than corner Si adatoms, by a factor of 1.6. This difference shows that the binding energy of the center Si adatom is smaller than that of the corner Si adatom by about 0.01eV. Empirical calculations using a cluster model of the Si(111)7×7 structure are performed, and the calculated results agree with an experimental finding that the center Si adatoms are extracted more frequently.