Using the interstitial electron surface model (IESM) developed in the accompanying part, we examined the structures and energetics of a number of organic fragments on Pt surfaces. Using nonlocal density functional methods (B3LYP) we find that organics covalently bond to the Pt(lll) surface with localized sigma bands to the surface Pt atoms, leading to tetrahedral hybridization of each carbon bonded to the surface. Thus, (i) CH3 prefers an on-top site (a bond energy of similar to 54 kcal/mol), (ii) CH2 prefers a 2-fold bridge site (a bond energy of similar to 104 kcal/mol), and (iii) CH prefers the fee 3-fold bridge site (a bond energy of similar to 167 kcal/mol). Similarly, C2H4 forms a strong (36 kcal/mal) di-sigma bond (the pi bond is BE = 8.5 kcal/mol), while CHCH2 forms a tri-sigma bond. The results for C2Hx/Pt-8 are in good agreement with available experimental results on Pt(lll) (pi- and di-sigma-bonded ethylene and ethylidyne). These results are used to obtain heats of formation (Delta H-f) for chemisorbed intermediates useful in estimating the energetics of various hydrocarbon intermediates on Pt surfaces. The application of these Delta H-f values is illustrated by considering ethylene hydrogenation and the decomposition of C2H4 on Pt(111).