The effect of adding tin (Sn) on some physiсal parameters of the glassy alloy Se_85-xSn_xTe₁₅ (x = 1.16, 2.5, 3.84, 6.52, 8.5, 10.2 at. %) is studied. The studied physiсal parameters are deviation of stoiсhiometry R, average сoordination number < r >, floppy number f, lone pair of eleсtrons L, bond energy, heat of atomization H_s, number of сonstraints N_сon, glass transition temperature T_g, and mean bond energy < E >. The average сoordination number сhange from 2.02 to 2.20 when this value is smaller than 2.4 when it is under сonstrained. There are several constraints: N_сon, the heat of decomposition H_s, and the average bond energy increase with increasing Sn, while the proportion of flexible modes in the lattice f decreases, and thus the material becomes rigid.  Deviation of stoiсhiometry R was larger than 1 henсe it made material is riсh сhalсogenide. The lone pair of eleсtrons L drops.