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I
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.
| SHELL | K | L | M | N | O | P | Q |
| SUB SHELL | He | Neon | Argon | Krypton | Xenon | Radon | Eka-radon |
| 1s | 2s 2p | 3s 3p | 3d 4s 4p | 4d 5s 5p | 4f 5d 6s 6p | 5f 6d 7s 7p | |
| Iodine | 1s22s22p63s23p63d104s24p64d105s25p5 | ||||||
| Symbol | 2P3/2 | ||||||
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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