In this paper, a detailed study to examine the influence of chalcogen S/Se mole % in the Ge28Sb12S60 −xSexglass system, with x = 0, 15, 30, 45 and 60, is presented that provides insight into the effect of chalcogen content on the glassnetwork and properties. Specifically, we report results of a systematic study to evaluate the relationship between compositional variation, glassproperties and dominant bonding configurations. These materials are important to applications in optics manufacturing where correlation of physical and optical properties is required to predict fabrication behavior and ultimate material performance. It has been found that the dominant bonds in the glass system change upon reaching a specific molar ratio (percentage, %) of chalcogen substitution, between 30 < x < 45 mol%, changing from Ge―Se to Sb―Se bonds as the dominant bond type. This singularity has been observed using micro-Raman spectroscopy and X-ray photoelectron spectroscopy. This effect of the dominant bond configurational change was also shown to impart changes in important physical properties including micro-hardness, thermal properties, and the glass' viscometric behavior. Results indicate that the observed dominant bond change was responsible for a constant value in the evolution of both the micro-hardness and calorimetric glass transition temperature. The viscosity was also affected by the change in dominant bond type, breaking the monotony of the viscosity evolution during the Ssubstitution, due to the total strength of the vitreous system which does not linearly increase.< Réduire