We present in situ scanning tunneling microscopy (STM) images with the resolution of isolated ≡ Si — O X groups on H-Si(111) in NaOH solutions with or without isopropyl alcohol [ X = H or — CH ( CH 3 ) 2 ] . The comparison of STM with geometric contours shows that the electronegativity of OH ligands enhances the local density of states and generates a surface potential distribution. The dependence of both observations with the radical X and the mechanisms of grafting are discussed.