The potential energy surfaces for the abstraction reactions of disilenes and digermenes with carbon tetrachloride have been characterized in detail using density functional theory (B3LYP/6-311G(d)), including zero-point corrections. Ten substituted disilene and digermene species, R2X=XR2 (X = Si, Ge; R = H, F, Cl, CH3, and SiH3 have been chosen in this work as model reactants. Of the two possible reaction paths, the Cl abstraction (path 1) and the CCl3 abstraction (path 2), the former is found to be more favorable, with a very low activation energy and a larger exothermicity. This is in accordance with available experimental observations. The activation barriers and enthalpies of the reactions are compared to determine the relative reactivity of disilene and digermene as well as the influence of substitution on the reaction potential energy surface. Our theoretical investigations indicate that, irrespective of disilene and digermene species, the more electropositive and/or the more bulky the substituents, the lower the activation barrier and the more exothermic the haloalkane abstraction. In short, electronic as well as steric factors play a dominant role in determining the chemical reactivity of the disilene or digermene species kinetically as well as thermodynamically. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.