The influence of the support ionicity on the adsorption of H, CHx (x = 2, 3), and O on supported Pt particles is investigated using density functional theory (DFT). The DFT calculations reveal that the importance of the 6s,p states for the Pt adsorbate bonding increases in the order Pt-O < Pt-CH2 < Pt-CH3 < Pt-H. Both the Pt-H and Pt-O bond strengths are strongly affected by changes in the support ionicity whereas the difference for the Pt-CHx bond strength is much smaller. The Pt-H bond strength is higher for ionic supports, whereas the Pt-O bond strength is higher for acidic or more covalent supports. These bond strength changes occur because the support ionicity has a large impact on both the Pt 6s,p and 5d states. On ionic supports with electron rich oxygen atoms, the 6s,p states are pushed toward the surface of a metal cluster where it can participate in H bonding, whereas on supports with electron poor oxygen atoms (existing in acidic supports or for supports with more covalent cations) the 6s,p states are attracted toward the metal-support interface. The Pt 5d states shift to lower binding energy (lower ionization potential) on ionic supports, where it bonds less effectively with the O adsorbate. These findings indicate that the hydrogen and oxygen coverage on Pt particles are strongly determined by the ionicity and acid/base properties of the support and therefore may be the most important for producing changes in the reactivity of Pt wit support ionicity in various hydrogenolysis, hydrogenation, and oxidation reactions.