Data on phase equilibria in the Cu-S, Ag-S, Zn-S, Cd-S, Hg-S, Sn-S and Pb-S systems are presented, and generalized experimental results on the crystal and electronic structure of twenty polymorphic phases of coarse- and nanocrystalline semiconductor copper, silver, zinc, cadmium, mercury, tin and lead sulfides. Information on the band gaps of all the considered sulfides generalized also. For the first time, using data on the effective masses of charge carriers and dielectric constants, information on the sizes of excitons in coarse-crystalline sulfides has been generalized. Taking into account the sizes of excitons, the size effects observed on the electronic (optical) properties of these sulfides in the nanocrystalline state are considered. It is shown that a decrease in the size of sulfide nanoparticles can be accompanied by a change in the stoichiometry of sulfides, as well as their lattice properties.