With DFT calculations, compared where possible with experimental data, molecular and electronic structure of the title compounds 1-5 (chalcogen=O, S, Se, Te and Po, respectively) and their radical ions was studied towards identification of regularities and peculiarities over a whole chalcogen pentad. Calculated properties of neutral molecules covered their geometries, atomic charges, bond orders and QTAIM descriptors, shapes and energies of π-MOs, ionization energy and electron affinity, NICSs, and MEPs; and those of radical ions included geometries, shapes and energies of π-SOMOs, electron spin density distributions, hyperfine coupling constants and g factors. In the most cases uniform patterns were obtained featuring only some particular peculiarities regarded to a certain chalcogen. The most important findings embrace reduced aromaticity of the heterocycles of 4 and 5 (NICS) and enlarged electrostatic contribution to their X-N bonds (QTAIM; X=Te, Po) as compared with 1-3. However, the ground-state patterns are not enough to explain known differences in heteroatom reactivity of the title compounds. It is suggested that the differences come mainly from reaction kinetics and thermodynamics where widely varied atomic dipole polarizability of the chalcogens should be essentially important.