ABSTRACT
There are only two stable elements in Group 16: selenium (Se) and tellurium (Te). Both resemble S in a number of geochemical properties; however, their behavior in the environment is more complex. Polonium (Po), natural isotope of the U-Ra transformation chain, also belongs to this group. These elements, which are nonmetals, but also considered metalloids, are highly mobile in the Earth’s crust and reveal both chalcophilic and siderophilic properties. All of these elements exist in variable valence states from −2 to +6 (Table 21.1).
