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H' at. wt. (natural) 1.007967
   at. wt. (H') 1.007822
   at. no. 1
   m.p. - 259.140C
   b.p. - 252.870C 
   density 0.08988 gm./l
   density (liquid) 70.8 gm/i. (-2530C)
   density (solid) 7016 gm/i. (-2620C)
   valence 1.

**Electronic configuration**
K	L	M	N	O	P	Q
1	2	3	4	5	6	7
s	s p	s p d	s p d f	s p d f	s p d f	s p d f
1

ASTATINE (Gr. astatos, unstable), At; at. wt. 210; at. no.85; valence probably 1,3, 5, or 7. Synthesized in 1940 by D. R. Corson, K. R. MacKenzie, and E. Segre' at the Univer- sity of California by bombarding bismuth with alpha- parlicles. The longest-lived isotope, At210, has a half-life of only 8.3 hours. More than twenty isotopes are now known. Minute quantities of At215, At218, and At219 exist in equilibrium in nature with naturally occurring uranium and thorium isotopes, and traces ofAt217 are in equilibrium with U233 and Np239 resulting from interaction of thorium and THE ELœMENTS+Coiitiiiued) uranium with naturally produced neutrons. The total amount of astatine present in the earth's crust, however, totals less than one ounce. Astatine can be produced by bombarding bismuth with energetic alpha particules to obtain the relatively long-lived At2 09-211, which can be distilled from the target by heating it in air. Only about 0.05 micrograms of astafine have been prepared to date. The "time of flight" mass spectrometer has been used to confirm that tjiis highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. The inter-halogen compounds Ati, AtBr, and AtCl are known to form, but it is not yet known if astatine forms diatomic astatine molecules. HAt and CH3At (methyl astatide) have been detected. Astatine is said to be more metallic than iodine, and like iodine, it probably accumulates in the thyroid gland.

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