The rutile titanium dioxide (TiO_2) (110) surface exposed to Cl_2 gas was examined using scanning probe microscopes. The Cl adatoms formed by Cl_2 dissociation were observed as bright spots in empty-state scanning tunneling microscope images. While 94% of the Cl adatoms were on the top of surface Ti atoms, the remaining 6% of the adatoms missed the on-top site. The Kelvin probe force microscope measurements revealed a local work function increase on the Cl adatoms. The electronegative Cl adatoms were proposed to accumulate electrons from the surface. The resultant dipole moments were directed from the vacuum to the surface, and hence the work function of the adatoms locally increased. identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/8787