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Selenium - Se General Information Discovery Selenium was discovered by J.J.Berzelius in 1817 in Stockholm, Sweden. Appearance Selenium exists as several allotropic forms. The most stable variety, crystalline hexagonal selenium, is a metallic grey colour. Crystalline monoclinic selenium is deep red. Amorphous selenium is either red (in powder form) or black (in vitreous form). Source Most of the world's selenium is obtained from the anode muds from electrolytic copper refineries. These muds are either roasted with soda or sulfuric acid, or smelted with soda to release the selenium. Selenium is found in a few rare minerals. Uses Selenium is both photovoltaic (converts light to electricity) and photoconductive (electrical resistance decreases with increased illumination). Selenium is therefore useful in photocells and solar cells. It can also convert a.c. electricity to d.c. electricity, so is extensively used in rectifiers. It is used by the glass industry, and to make stainless steel. It is also used in photocopiers. Biological Role Selenium is an essential trace element but is toxic in excess. It is carcinogenic and teratogenic. Hydrogen selenide and other selenium compounds are extremely toxic. General Information Selenium burns in air, is unaffected by water and reacts with concentrated nitric acid and alkalis. |
| Physical Information | |||
| Atomic Number | 34 | ||
| Relative Atomic Mass (12C=12.000) | 78.96 | ||
| Melting Point/K | 490 | ||
| Boiling Point/K | 958.1 | ||
| Density/kg m-3 | 4790 (293K) | ||
| Ground State Electron Configuration | [Ar]3d104s24p4 | ||
| Electron Affinity(M-M-)/kJ mol-1 | -195 |
| Key Isotopes | ||||||
| nuclide | 74Se | 75Se | 76Se | 77Se | 78Se | |
| atomic mass | 73.923 | 74.923 | 75.919 | 76.920 | 77.917 | |
| natural abundance | 0.9% | 0% | 9% | 7.6% | 23.5% | |
| half-life | stable | 120.4 days | stable | stable | stable | |
| nuclide | 80Se | 82Se | ||||
| atomic mass | 79.917 | 81.917 | ||||
| natural abundance | 49.6% | 9.4% | ||||
| half-life | stable | stable | ||||
| Other Information | ||
| Enthalpy of Fusion/kJ mol-1 | 5.1 | |
| Enthalpy of Vaporisation/kJ mol-1 | 90 | |
| Oxidation States | ||
| main | Se+4, Se+6 | |
| others | Se-2, Se+1, Se+2 | |
| Covalent Bonds /kJ mol-1 | ||
| Se - H | 305 | |
| Se - C | 245 | |
| Se - O | 343 | |
| Se - F | 285 | |
| Se - Cl | 245 | |
| Se - Se | 330 | |
| Ionisation Energies/kJ mol-1 | ||
| M - M+ | 940.9 | |
| M+ - M2+ | 2044 | |
| M2+ - M3+ | 2974 | |
| M3+ - M4+ | 4144 | |
| M4+ - M5+ | 6590 | |
| M5+ - M6+ | 7883 | |
| M6+ - M7+ | 14990 | |
| M7+ - M8+ | 19500 | |
| M8+ - M9+ | 23300 | |
| M9+ - M10+ | 27200 | |
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