Monolayers composed of difluoroacetate (CF2HCOO-) and trifluoroacetate (CF3COO-) were prepared on an atomically flat surface of titanium oxide. The chemical identity of individual adsorbed molecules was determined in the mixed monolayers by noncontact atomic force microscopy. The permanent dipole moment of the fluorine-substituted terminal groups perturbed the microscope topography via the electrostatic coupling with the probe tip.