Tennessine 17 in the periodic table, below the five halogens; fluorine, chlorine, bromine, iodine, and astatine, each of which has seven valence electrons with a configuration of . For tennessine, being in the seventh period (row) of the periodic table, continuing the trend would predict a valence electron configuration of , and it would therefore be expected to behave similarly to the halogens in many respects that relate to this electronic state. However, going down group 17, the metallicity of the elements increases; for example, iodine already exhibits a metallic luster in the solid state, and astatine is often classified as
Fluorine perchlorate Fluorine perchlorate Perchloryl Hypofluorite is the rarely encountered chemical compound of fluorine, chlorine, and oxygen with the chemical formula or . It is an extremely unstable gas that explodes spontaneously and has a penetrating odor. One synthesis uses fluorine and perchloric acid, though the action of ClF on water is another method. Another method of synthesis involves the thermal decomposition of tetrafluoroammonium perchlorate, , which yields very pure that may be manipulated and frozen without explosions. Fluorine perchlorate is not analogous to perchloric acid because the fluorine atom does not exist as a positive ion. It contains an oxygen atom