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Iodine - I General Information Discovery Iodine was discovered by B. Courtois in 1811 in Paris, France. Appearance Iodine is a blue-black, shiny crystalline solid which sublimes at room temperature into a purple gas with an irritating odour. Source Iodine (as iodide) occurs sparingly (0.05 parts per million) in sea-water. From this source it is assimilated by seaweeds. It is also found in brines from deposits left by the evaporation of old seas, and in brackish waters from oil and salt wells. Iodine is obtained commercially by extracting iodine vapour from processed brine, by ion exchange of brine or by liberating iodine from iodate obtained from nitrate ores. Uses Iodine has many commercial uses including pharmaceuticals, photographic chemicals, printing inks and dyes, catalysts and animal feeds. Iodide in small amounts is often added to table salt in order to avoid thyroid disease. Biological Role Iodine is an essential element, lack of which causes problems with the thyroid gland. The artificial radioisotope, 131I, with a half-life of 8 days, is used in treating cancerous thyroid glands. A solution of potassium iodide and iodine, or of iodine in ethanol, has germicidal effects, and was used for the external treatment of wounds. If iodine is in contact with the skin it can cause lesions, and iodine vapour is extremely irritating to the eyes and mucous membranes. General Information Iodine forms compounds with many elements, but is less active than the other halogens. It dissolves readily in chloroform, carbon tetrachloride and carbon disulfide to form beautiful purple solutions. It is only sparingly soluble in water. Organic iodine compounds are important in organic chemistry. |
| Physical Information | |||
| Atomic Number | 53 | ||
| Relative Atomic Mass (12C=12.000) | 126.9 | ||
| Melting Point/K | 387 | ||
| Boiling Point/K | 458 | ||
| Density/kg m-3 | 4930 (293K) | ||
| Ground State Electron Configuration | [Kr]4d105s25p5 | ||
| Electron Affinity(M-M-)/kJ mol-1 | -295 |
| Key Isotopes | ||||||
| nuclide | 123I | 125I | 127I | 129I | 131I | |
| atomic mass | 126.9 | |||||
| natural abundance | 0% | 0% | 100% | 0% | 0% | |
| half-life | 13.3 h | 60.2 days | stable | 1.7x107 yrs | 8 days |
| Other Information | ||
| Enthalpy of Fusion/kJ mol-1 | 15.27 | |
| Enthalpy of Vaporisation/kJ mol-1 | 41.67 | |
| Oxidation States | ||
| main | I-1 | |
| others | I0, I+3, I+5, I+7 | |
| Covalent Bonds /kJ mol-1 | ||
| I - H | 299 | |
| I - C | 228 | |
| I - O | 234 | |
| I - F | 280 | |
| I - Cl | 208 | |
| I - I | 151 | |
| I - Si | 234 | |
| I - P | 184 | |
| Ionisation Energies/kJ mol-1 | ||
| M - M+ | 1008.4 | |
| M+ - M2+ | 1845.9 | |
| M2+ - M3+ | 3200 | |
| M3+ - M4+ | 4100 | |
| M4+ - M5+ | 5000 | |
| M5+ - M6+ | 7400 | |
| M6+ - M7+ | 8700 | |
| M7+ - M8+ | 16400 | |
| M8+ - M9+ | 19300 | |
| M9+ - M10+ | 22100 | |
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