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I

IODINE

(Gr. jodes, violet )

I   at. wt. 126.9045
     at. no. 53
     m.p.   113.50°C
     b.p.    184.350.8°C
     sp. gr. 4.93 (20°C)
     valence 1, 3, 5, or 7.

**Electronic configuration**
SHELL	K	L	M	N	O	P	Q
SUB SHELL	He	Neon	Argon	Krypton	Xenon	Radon	Eka-radon
SUB SHELL	1s	2s 2p	3s 3p	3d 4s 4p	4d 5s 5p	4f 5d 6s 6p	5f 6d 7s 7p
Iodine	1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁵
Symbol	²P_3/2

Iodine was discovered by Courtois in 1811. Iodine, a halogen, occurs sparingly in the form of iodides in sea water from which it is assimilated by seaweeds, in Chilean saltpeter and nitrate-bearing earth, known as caliche, in brines from old sea deposits, and in brackish waters from oil and salt wells. Ultrapure iodine can be obtained from the reaction of potassium iodide with copper sulfate. Several other methods of isolating the element are known. Iodine is a bluish-black, lustrous solid, volatilizing at ordinary temperatures into a blue-violet gas with an irritating odor; it forms compounds with many elements, but is less active than the other halogens, which displace it from iodides. Iodine exhibits some metallicAike properties. It dissolves readily in chloroform, carbon tetra- chloride, or carbon disulfide to form beautiful purple solutions. It is only slightly soluble in water. Iodine com- pounds are important in organic chemistry and very useful in medicine. Twenty-four isotopes are recognized. Only one stable isotope, 1127, is found in nature. The artificial radio- scope 1131, 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 iedates (K103). Lack of iodine is the cause of goiter. The iodide and thyroxin, which contain iodine, are used internally in medicine, and a solution of KI and iodine in alcohol is used for external wounds. Potassium iodide finds use in photo- graphy. The deep blue color with starch solution is charac- teristic of the free element. Care should be taken in handling and using iodine as contact with the skin can cause lesions; iodine vapor is intensely irritating to the eyes and mucous membranes. The recommended maximum allowable con- centration in air is 1 mg/cu. meter.

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I

IODINE

(Gr. jodes, violet )

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