Theoretical calculations of images obtained by a scanning tunneling microscope of atomic adsorbates on a metal surface are presented. B, C, N, O, Na, Al, S, K, Se, Te and Pt atoms adsorbed on a Pt(111) surface are considered within the electron scattering quantum chemical method. The resulting pattern is very dependent on the nature of the atom, and ranges from a 2 bump for large and electropositive metal atoms (K, Pt) to a 0.35 depression for the small and electronegative oxygen atom. The tunneling amplitude is decomposed into two contributions which interfere together to yield the final contrast. The current arising from the interaction between the tip and the surface Pt atoms is reduced in the vicinity of the adsorbate, and contributes a dip to the STM image for all considered atoms. The additional through-atom channel arising from the interaction between the tip and the atomic orbitals of the adsorbate itself shows a bump. In the case of small and electronegative atoms like O and N, this bump is weak and the final image is a hole. With more polarisable elements, the through-adsorbate current is larger and the final image appears as a bump, with a height depending on the species.