Overview. Astatine is a member of the halogen family, elements in Group 17 (VIIA) of the periodic table. It is one of the rarest elements in the universe. Scientists believe that no more than 25 grams exist on the Earth's surface.statine is far too rare to have any uses. Some research suggests a possible medical use, however. Astatine is similar to the elements above it in Group 17 (VIIA) of the periodic table, especially iodine.