The last element Astatine is radioactive and is very short lived hence generally excluded from the study. It is one of the rarest elements in the universe. A: The number of valence electrons starts at one for elements in group 1. Astatine is the heaviest of the halogens and is essentially unavailable in nature with less than one teaspoon of the element found in the Earth’s crust at any one time. Astatine is a member of the halogen family, elements in Group 17 (VIIA) of the periodic table. In 1940, D. R. Corson, K.R. Astatine can be produced by bombarding bismuth with energetic alpha particles to obtain the relatively long-lived 209-211 At, which can be distilled from the target by heating in air. Astatine is a halogen and it is quite possible that it accumulates in the human thyroid just like iodine. The word halogen is derived from the Greek words Halos (Sea Salt) and Genes (Producer). If you could ever isolate enough of this stuff astatine would be an even darker purple solid than iodine. Astatine is also studied in a few nuclear research laboratories in which the high radioactivity of the element requires a special kind of handling techniques and precautions to be taken. Astatine can also react with hydrogen to form hydrogen astatide, which when dissolved in water, forms hydroastatic acid. Bromine liquid evaporates easily at room temperatures emitting an orange vapor. A more reactive halogen displaces a less reactive one from its compound. All isotopes of astatine are radioactive and decay into other elements. The astatine halogen bond also completes a periodic set that has attracted growing interest in recent years. Q: Based on their position in the periodic table from the Figure above, how many valence electrons do you think halogens have? Astatine has found uses in medicine even though it is radioactive and decays quickly. astatine. Scientists believe that no more than 25 grams exist on the Earth's surface. As a result, it is one of the least common elements on Earth. Astatine is radioactive and rapidly decays to other, more stable elements. Figure \(\PageIndex{1}\): Halogens reside in group 17 of the periodic table, in this case the green column on the right side of the table. The first halogen to be isolated and recognized as an element was chlorine. Astatine-211 is sometimes used as a radioactive tracer and in cancer treatment. As a result, it is one of the least common elements on Earth. Why? Astatine is the least chemically reactive of the halogens and exhibits the most metallic properties of the halogen group. iodine (brown) and sodium chloride. Would you expect Astatine to be more or less reactive than iodine? 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