where is iodine found in the periodic table
heaviest of the stable halogens
title: Iodine text: Iodine Iodine is a chemical element with symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a lustrous, purple-black non-metallic solid at standard conditions that sublimes readily to form a violet gas. The elemental form was discovered by the French chemist Bernard Courtois in 1811. It was named two years later by Joseph Louis Gay-Lussac from this property, after the Greek "ἰώδης" "violet-coloured". Iodine occurs in many oxidation states, including iodide (I), iodate (), and the various periodate anions. It is the least abundant of the stable halogens, being the sixty-first most abundant element. title: Iodine text: who identified iodine first, but both scientists acknowledged Courtois as the first to isolate the element. Iodine is the fourth halogen, being a member of group 17 in the periodic table, below fluorine, chlorine, and bromine; it is the heaviest stable member of its group. (The scarce and fugitive fifth halogen, the radioactive astatine, is not well-studied due to its expense and inaccessibility in large quantities, but appears to show various unusual properties due to relativistic effects.) Iodine has an electron configuration of [Kr]4d5s5p, with the seven electrons in the fifth and outermost shell being its valence electrons. Like the title: Iodine text: by mass action due to the precipitation of the insoluble salt. Iodine is the least abundant of the stable halogens, comprising only 0.46 parts per million of Earth's crustal rocks (compare: fluorine 544 ppm, chlorine 126 ppm, bromine 2.5 ppm). Among the eighty-four elements which occur in significant quantities (elements 1–42, 44–60, 62–83, and 90–92), it ranks sixty-first in abundance. Iodide minerals are rare, and most deposits that are concentrated enough for economical extraction are iodate minerals instead. Examples include lautarite, Ca(IO), and dietzeite, 7Ca(IO)·8CaCrO. These are the minerals that occur as trace impurities in the caliche, found in Chile, title: Iodine in biology text: Iodine in biology Iodine is an essential trace element in biological systems. It has the distinction of being the heaviest element commonly needed by living organisms as well as the second-heaviest known to be used by any form of life (only tungsten, a component of a few bacterial enzymes, has a higher atomic number and atomic weight). It is a component of biochemical pathways in organisms from all biological kingdoms, suggesting its fundamental significance throughout the evolutionary history of life. Iodine is critical to the proper functioning of the vertebrate endocrine system, and plays smaller roles in numerous other organs, title: Iodine text: molecular weight of T and 59% of T. Fifteen to 20 mg of iodine is concentrated in thyroid tissue and hormones, but 70% of all iodine in the body is found in other tissues, including mammary glands, eyes, gastric mucosa, fetal thymus, cerebro-spinal fluid and choroid plexus, arterial walls, the cervix, and salivary glands. In the cells of those tissues, iodide enters directly by sodium-iodide symporter (NIS). The action of iodine in mammary tissue is related to fetal and neonatal development, but in the other tissues, it is (at least) partially unknown. Recommendations by the United States Institute of Medicine