| 21. | Astatine is the rarest naturally occurring element.
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| 22. | The most important isotope is astatine-211, the only one in commercial use.
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| 23. | There are no stable isotopes of astatine.
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| 24. | The inclusion of antimony, polonium, and astatine as metalloids also has been questioned.
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| 25. | Several authors have commented on the metallic nature of some of the properties of astatine.
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| 26. | Additionally, astatine has no stable isotopes.
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| 27. | Corson and his colleagues classified astatine as a metal on the basis of its analytical chemistry.
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| 28. | All halogens have been observed as diatomic molecules, except for astatine, which is uncertain.
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| 29. | According to your web page, the first ionization energy of astatine is 20KJ / mol.
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| 30. | Its alpha decay half-life is in accordance : the shortest of all astatine isotopes.
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