The bond length and energy changes of the constituents of alloys relative to their pure crystal values are calculated from an extension of Harrison’s method. It is demonstrated that the already weak HgTe bonds are destabilized by adjacent CdTe, HgS, or HgSe, but are stabilized by ZnTe. It is also argued that dislocation energies and the hardness of semiconductors vary as a high inverse power of the bond length of the constituents. Hence, the shorter ZnTe bond as an additive should improve the structural properties of HgTe and CdTe. Experiments that support these predictions are noted. The electronic transport properties of 0.1 eV band gap HgZnTe are about the same as those of HgCdTe, and the structural properties of the Zn compound are superior; thus, we conclude that HgZnTe is likely to be the better material for IR devices.