* Iodine and astatine are members of the halogen family:
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IODINE / I / 53
At room temperature, iodine is a dark shiny nonmetallic solid that
sublimes -- goes from solid to vapor -- easily. Iodine is
generally found in nature in the form of the stable isotope
I<127/53>, though traces of radioactive iodine isotopes can be
found as products of radioactive series.
atomic weight: 126.90447
abundance: 64th
density: 4.93 gm/cc
melting point: 114 C
boiling point: 184 C
valence: 1 3 5 7
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The "I-" ion is known as "iodide". Iodine also has some small-scale applications, being derived from brines and with production of over a hundred thousand tonnes a year. It is used in dyes and disinfectants; solutions of iodine used to be a popular household disinfectant, but iodine stings a good deal and stains, so it has been largely replaced by more convenient disinfectants. The human thyroid gland needs traces of iodine to function properly, swelling up in a condition known as "goiter" if iodine is not available, and so salt is generally "iodized" to ensure that people get their daily requirement of iodine. Interestingly, there seems to be little or no controversy over this practice, in contrast to fluoridation of water supplies, despite the fact that too much iodine is toxic.
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ASTATINE / At / 85
Astatine is highly radioactive, the most stable isotope being
At<210/85>, with a half-life of 8 hours.
atomic weight: 210
abundance: negligible
density: ?
melting point: 300 C?
boiling point: 340 C?
valence: 1 3 5 7
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Astatine's bulk properties are a matter of educated speculation, for the simple reason that it doesn't last long enough to be accumulated in bulk.
