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, gaseous radioactive chemical element; symbol Rn; at. no. 86; mass no. of most stable isotope 222; m.p. about −71°C;; b.p. −61.8°C;; density 9.73 grams per liter at STP; valence usually 0. Radon is colorless and the most dense gas known.
..... Click the link for more information. ; thoriumthorium
[from Thor], radioactive chemical element; symbol Th; at. no. 90; mass number of most stable isotope 232; m.p. about 1,750°C;; b.p. about 4,790°C;; sp. gr. 11.7 at 20°C;; valence +4.
Thorium is a soft, ductile, lustrous, silver-white, radioactive metal.
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The conventional name for radon-220. Symbolized Tn.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.