Other compounds
Tetraselenium tetranitride, Se4N4, is an explosive orange compound analogous to tetrasulfur tetranitride (S4N4).
Five of these, 74Se, 76Se, 77Se, 78Se, 80Se, are stable, with 80Se being the most abundant (49.6% natural abundance). Also naturally occurring is the long-lived primordial radionuclide 82Se, with a half-life of 9.2×1019 years. The non-primordial radioisotope 79Se also occurs in minute quantities in uranium ores as a product of nuclear fission. Selenium also has numerous unstable synthetic isotopes ranging from 64Se to 95Se; the most stable are 75Se with a half-life of 119.78 days and 72Se with a half-life of 8.4 days. Isotopes lighter than the stable isotopes primarily undergo beta plus decay to isotopes of arsenic, and isotopes heavier than the stable isotopes undergo beta minus decay to isotopes of bromine, with some minor neutron emission branches in the heaviest known isotopes. Chemical compounds
Selenium compounds commonly exist in the oxidation states −2, +2, +4, and +6. Chalcogen compounds
Selenium forms two oxides: selenium dioxide (SeO2) and selenium trioxide (SeO3).