The chemistry of 1-iodopropane, 1-iodobutane, 2-iodobutane, 1-iodo-2-methylpropane, 2-iodo-2-methylpropane, 1-iodopentane, and 1-iodohexane on Ni(100) surfaces has been studied by using temperature-programmed desorption and X-ray photoelectron spectroscopy. Below 100 K all the compounds adsorb molecularly through the iodine atom. The hydrocarbon chain orients parallel to the surface at first, but flips as the coverage increases, and becomes perpendicular to the surface at saturation. The C-I bond dissociates between 120 and 180 K to yield the corresponding alkyl fragment on the surface. At higher temperatures the alkyl groups decompose further, directly to carbon and hydrogen at low coverages (below half-saturation), but mainly to a mixture of alkanes and alkenes at saturation. The change in the ratio between alkane and alkene production was examined with respect to both the degree of substitution and the length of the carbon chain. It was found that the beta-hydride elimination that yields the alkenes is favored over the reductive elimination responsible for the alkane formation in alkyl species with a large number of beta-hydrogens, even in the presence of coadsorbed hydrogen on the surface. On the other hand, the hydrogenation steps were seen to dominate in the coadsorbed systems for alkyl species with a small number of beta-hydrogen atoms. An increase in chain length has the effect of decreasing the alkene-to-alkane ratio further.