The potential energy surfaces for the chemical reactions of tetrasilyl-substituted trimetallaallenes containing two cumulative EE double bonds, where E = C, Si, Ge, Sn, and Pb, are studied using density functional theory (B3LYP/LANL2DZ). Two types of chemical reactions, methanol addition and intramolecular 1,2-silyl migration, are used to study the reactivity of these allene analogues. The theoretical investigations suggest that the relative reactivity increases in the order: >CCC< ≪ >SiSiSi< < >GeGeGe< < >SnSnSn< < >PbPbPb<. That is, the heavier the atomic weight of the group 14 atom (E), the more reactive is the >EEE< towards chemical reactions. Electronic (due to the group 14 element E) and steric (due to four bulky t-Bu₂MeSi groups) factors play a key role in determining both the geometrical structures and the reactivity of the tetrasilyl-substituted trimetallaallenes, from both kinetic and thermodynamic viewpoints. 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, such as the reactivities and the reaction mechanisms of heavy allenes, to be made.