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Iodine: Elements
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Iodine is a dark-gray/purple-black solid that sublimes at standard temperatures into a purple-pink gas that has an irritating odor. This halogen forms compounds with many elements, but is less active than the other members of its Group VII (halogens) and has some metallic-like properties. Iodine dissolves easily in chloroform, carbon tetrachloride, or carbon disulphide to form purple solutions (It is only slightly soluble in water, giving a yellow solution). The deep blue color of starch-iodine complexes is produced only by the free element.
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Iodine is a relatively rare element, ranking about 62nd in abundance on Earth, but its compounds are widespread in seawater, soil, and rocks. Iodine is obtained from brines and from Chilean nitrate ores in which it occurs as an impurity. To a lesser extent, iodine is ... derived from sea organisms, such as brown seaweeds, that concentrate iodine in their tissues.
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Iodine under standard conditions is a dark-purple/dark-brown solid. It can be seen apparently subliming at standard temperatures into a violet-pink gas that has an irritating odor. This halogen forms compounds with many elements, but is less reactive than the other members of its Group VII (halogens) and has some metallic light reflectance.
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Iodine compounds are important in organic chemistry and very useful in medicine. Iodides, and thyroxine which contains iodine, are used internally in medicine, and as a solution of KI and iodine in alcohol is used for external wounds. Potassium iodide finds use in photography. The deep blue color with starch solution is characteristic of the free element.
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Iodine and its compounds are primarily used in medicine, photography and in dyes. Although its high atomic number makes it rare in the solar system and earth's crust, the iodides are very soluble in water, and the element is concentrated in seawater. This mechanism helps to explain how the element came to be required in trace amounts by all animals and some plants, being by far the heaviest element known to be necessary to living organisms.
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Iodine is an essential dietary element necessary for normal development and function of all vertebrates. Its sole physiological function is as a constituent of the thyroid hormones, thyroxine and triiodothyronine. It is removed from the blood by the thyroid gland for storage in organic form where it is found as iodinated amino acids in peptide linkage in thyroglobulin, a highmolecular weight protein.
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