Element Astatine, At, Halogene

Before its actual discovery the existence of element 85 was known as eka-iodine predicted and named by D.I. Mendeleyev. Reports about its discovery appeared several times, but however no one of them was confirmed. One of the isotopes, no stable isotopes.

Halogene Astatine is the rarest of natural elements. The outer 1.6 km deep layer of the Earth's crust only 70 mg astatine had been found. It is permanently present because the most short-life isotopes are constituent part of the radioactive series of Uranium-235 and Uranium-238. The rate of their natural synthesis equals to the radioactive decay, so astatine total amount in the crust is unchangeable.