Element Astatine, At, Halogene
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Astatine History
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, astatine-211 had been obtained by Dale R. Corson, Kenneth R. Mackenzie, and Emilio Segre, who synthesized the isotope astatine-211 by bombarding bismuth with accelerated alpha-particles. The half-life of this isotope turned out to be mere 7.2 hours. It has been named astatine in the articles of the discoverers published in the "Nature" magazine in 1947 (Nature, 159, 24, 1947). They have named the new element astatine, from the Greek astatos which means restless, unstable, because the element has no stable isotopes.
Astatine Occurrence
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.
Astatine Neighbours
Elements Periodic Table |