Iodine and its compounds are primarily used in medicine, photography, and dyes. Iodine is rare in the solar system and Earth's crust. The iodides are very soluble in water, and the element is concentrated in seawater.
Iodine (pronounced /ˈaɪ.ɵdaɪn/ EYE-o-dyne, /ˈaɪ.ɵdɨn/ EYE-o-dən, or in chemistry /ˈaɪ.ɵdiːn/ EYE-o-deen; from Greek: ιώδης iodes meaning violet (or purple), is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons. Chemically, iodine is the second least reactive of the halogens, and the second most electropositive halogen, trailing behindastatine in both of these categories. However, the element does not occur in the free state in nature. As with all other halogens (members of Group 17 in the periodic table), when freed from its compounds iodine forms diatomic molecules.
Iodine and its compounds are primarily used in medicine, photography, and dyes. Iodine is 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 the heaviest element commonly used by living organisms (onlytungsten, used in enzymes by a few bacteria, is heavier.
Iodine compounds are important in organic chemistry and very useful in medicine.
Thirty isotopes are recognized. Only one stable isotope, 127I is found in nature.
The artificial radioisotope 131I, with a half-life of 8 days, has been used in treating the thyroid gland.
The most common compounds are the iodides of sodium and potassium (KI) and the iodates (KIO3).
Lack of iodine is the cause of goiter.
Iodides, and thyroxin 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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