Chemical modification of catalytic surfaces by adatoms adsorption is one of the most common methods for designing new (electro)catalytic materials. In this work, the interaction of single bismuth and tellurium adatoms with model platinum basal planes has been investigated using density functional theory to explore changes in the electronic properties of these systems. Calculations indicate that both adatoms are stable, and there is a charge transfer from the adsorbate to the surface in all the systems. As the result, the work function of Pt surfaces lowers and a trend: (100) > (110) > (111) emerges, different from (111) > (100) > (110) seen for the pristine planes. Both Bi and Te cause a noticeable shift in the d-band center of the surfaces, indicating a significant impact of these adatoms on Pt catalytic properties, as experimentally reported. For the Bi/Pt(111), the only system for which similar data has been described, results are in good agreement to previous studies. Results allow to gain insights at atomic-level into adatom-induced changes in electronic properties of Pt, which in turn shed light on key factors that control Pt catalytic activity toward model reactions. In this context, it is found that in contrast to the Bi/Pt(111) system, adatom's electronegativity cannot be considered as an effective descriptor for the enhanced activity of other Bi/Pt, or Te/Pt systems for the oxidation of organic molecules. Contrarily, calculated data offer a reasonable explanation for the reported inhibition of the hydrogen evolution reaction on Bi/Pt and Te/Pt surfaces in light of the substrate's adatom-induced strain.