| Atomic Mass | 78.971 |
|---|---|
| Electron Configuration | [Ar]4s23d104p4 |
| Oxidation States | +6, +4, -2 |
| Year Discovered | 1817 |
| Atomic Mass | 78.971 |
|---|---|
| Electron Configuration | [Ar]4s23d104p4 |
| Oxidation States | +6, +4, -2 |
| Year Discovered | 1817 |
| Element Name | Selenium |
|---|---|
| Element Symbol | Se |
| InChI | InChI=1S/Se |
| InChIKey | BUGBHKTXTAQXES-UHFFFAOYSA-N |
| Atomic Weight |
78.971(8) 78.971 78.96 78.971(8) |
|---|---|
| Electron Configuration |
[Ar]4s23d104p4 |
| Atomic Radius |
Van der Waals Atomic Radius : 190 pm (Van der Waals) Empirical Atomic Radius : 115pm (Empirical) Covalent Atomic Radius : 120(4) pm (Covalent) |
| Oxidation States |
+6, +4, -2 6, 5, 4, 3, 2, 1, -1, -2 (a strongly acidic oxide) |
| Ground Level |
3P2 |
| Ionization Energy |
9.752 eV 9.752368 ± 0.000006 eV |
| Electronegativity |
Pauling Scale Electronegativity : 2.55(Pauling Scale) Allen Scale Electronegativity : 2.424(Allen Scale) |
| Electron Affinity |
2.021eV 2.12eV |
| Atomic Spectra |
Lines Holdings Levels Holdings |
| Physical Description |
Solid |
| Element Classification |
Non-metal |
| Element Period Number |
4 |
| Element Group Number |
16 - Chalcogen |
| Density |
4.809 grams per cubic centimeter |
| Melting Point |
493.65 K (220.5°C or 428.9°F) 221°C |
| Boiling Point |
958 K (685°C or 1265°F) 685°C |
| Estimated Crustal Abundance |
5×10-2 milligrams per kilogram |
| Estimated Oceanic Abundance |
2×10-4 milligrams per liter |
The name derives from the Greek Selene, who was the Greek goddess of the Moon because the element is chemically found with tellurium (Tellus was the Roman goddess of the Earth). Selenium was discovered by the Swedish chemist Jöns Jacob Berzelius in 1817, while trying to isolate tellurium in an impure sample.
Selenium was discovered by Jöns Jacob Berzelius, a Swedish chemist, in 1817 after analyzing an impurity that was contaminating the sulfuric acid (H2SO4) being produced at a particular factory in Sweden. Originally believing the material was tellurium, Berzelius eventually realized that it was actually a previously unknown element. Selenium occurs in minerals such as eucairite (CuAgSe), crooksite (CuThSe) and clausthalite (PbSe), but these minerals are too rare to use as a major source of selenium. Today, most selenium is obtained as a byproduct of refining copper.
From the Greek word Selene, moon. Discovered by Berzelius in 1817, who found it associated with tellurium (named for the earth).
| Year | Atomic Weight (uncertainty) [u] | Reference |
|---|---|---|
| 2013 | 78.971(8) | https://doi.org/10.1515/pac-2015-0305 |
| 1969 | 78.96(3) | https://doi.org/10.1351/pac197021010091 |
| 1934 | 78.96 | https://doi.org/10.1039/JR9340000499 |
| 1903 | 79.2 | https://doi.org/10.1021/ja02003a001 |
| 1902 | 79.1 | https://doi.org/10.1007/BF01370337 |
Selenium exists in several allotropic forms, although three are generally recognized. Selenium can be prepared with either an amorphous or a crystalline structure. The color of amorphous selenium is either red (in powder form) or black (in vitreous form). Crystalline monoclinic selenium is a deep red; crystalline hexagonal selenium, the most stable variety, is a metallic gray.
Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for photographic use, as well as solar cells. Selenium is also able to convert a.c. electricity to d.c., and is extensively used in rectifiers. Below its melting point, selenium is a p-type semiconductor and has many uses in electronic and solid-state applications.
Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element; however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions.
Selenium's resistance to the flow of electricity is greatly affected by the amount of light shining on it. The brighter the light, the better selenium conducts electricity. This property has made selenium useful in devices that respond to the intensity of light, such as electric eyes, photo cells, light meters for cameras and copiers. Selenium can also produce electricity directly from sunlight and is used in solar cells. Selenium is also a semiconductor and is used in some types of solid-state electronics as well as in rectifiers, devices which convert alternating current electricity into direct current electricity. In addition to its use in electrical devices, selenium is also used to make a ruby-red color in glasses and enamels, as a photographic toner and as an additive to stainless steel.
Selenium forms few inorganic compounds, none of which are commercially important. They include selenious acid (H2SeO3), selenium dichloride (SeCl2) and selenium oxychloride (SeOCl2).
Selenium is used in Xerography for reproducing and copying documents, letters, etc. It is used by the glass industry to decolorize glass and to make ruby-colored glasses and enamels. It is also used as a photographic toner, and as an additive to stainless steel.
See more information at the Selenium compound page.
| CID | Name | Formula | SMILES | Molecular Weight |
|---|---|---|---|---|
| 6326970 | selenium | Se | [Se] | 78.97 |
| 107674 | selenium(2-) | Se-2 | [Se-2] | 78.97 |
| 25087178 | selenium-80 | Se | [80Se] | 79.91652 |
| 5460640 | selenium(1-) | Se- | [Se-] | 78.97 |
| 6328176 | selenium-75 | Se | [75Se] | 74.9225229 |
| 6335823 | selenium-79 | Se | [79Se] | 78.918499 |
| 6337549 | selenium-82 | Se | [82Se] | 81.916700 |
| 6337558 | selenium-78 | Se | [78Se] | 77.917309 |
| 6337661 | selenium-73 | Se | [73Se] | 72.92675 |
| 11332415 | selenium-77 | Se | [77Se] | 76.9199141 |
| 6337536 | selenium-70 | Se | [70Se] | 69.93352 |
| 6337550 | selenium-83 | Se | [83Se] | 82.91912 |
| 6337578 | selenium-81 | Se | [81Se] | 80.91799 |
| 9793691 | selenium-72 | Se | [72Se] | 71.92714 |
| 104791 | selenium(4+) | Se+4 | [Se+4] | 78.97 |
| 104869 | selenium(6+) | Se+6 | [Se+6] | 78.97 |
| 156022704 | selenium-82(2-) | Se-2 | [82Se-2] | 81.916700 |
| 156022705 | selenium-82(4+) | Se+4 | [82Se+4] | 81.916700 |
| 156022706 | selenium-82(6+) | Se+6 | [82Se+6] | 81.916700 |
| 6397238 | selenium(1+) | Se+ | [Se+] | 78.97 |
| 10103113 | selenium-71 | Se | [71Se] | 70.93221 |
| 11355436 | selenium-76 | Se | [76Se] | 75.9192137 |
| 131708383 | selenium-74 | Se | [74Se] | 73.9224759 |
Hydrogen selenide at a concentration of 1.5 ppm is intolerable to man. Selenium occurs in some solid in amounts sufficient to produce serious effects on animals feeding on plants, such as locoweed, grown in such soils. Exposure to selenium compounds (as Se) in air should not exceed 0.2 mg/m3 (8-hour time-weighted average - 40-hour week).
| Stable Isotope Count | 6 |
|---|---|
| Summary | Naturally selenium contains six stable isotopes. Fifteen other isotopes have been characterized. The element is a member of the sulfur family and resembles sulfur both in its various forms and in its compounds. |
Molecules, atoms, and ions of the stable isotopes of selenium possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of selenium in natural terrestrial materials (Fig. IUPAC.34.1).
![Fig. IUPAC.34.1: Variation in the isotope-amount ratio n(⁸²Se)/n(⁷⁶Se) of selected selenium-bearing materials (modified from [273]).](https://pubchem.ncbi.nlm.nih.gov/images/iupac/j_pac-2015-0703_fig_052.jpg)
75Se (with a half-life of 120 days) is used for X-ray radiography of welds to visualize welds and ensure that each weld is appropriate for its purpose [274].
75Se-selenomethionine (organic compound that combines to form proteins, found in Brazil nuts and soybeans) has been used to study the production of digestive enzymes (biological catalysts that accelerates chemical reactions) [275]. Selenium stable isotopes are used in metabolic studies to monitor selenium intake and output [276], [277].
77Se and 78Se are used to produce the therapeutic radioisotope 77Br via the 77Se (n, p) 77Br and the 78Se (n, 2p) 77Br reactions, respectively. 80Se is used to produce 80mBr via the reaction 80Se (n, p) 80mBr. The m the superscript of 80mBr indicates a metastable state of the isotope.
| Isotope | Atomic Mass (uncertainty) [u] | Abundance (uncertainty) | |
|---|---|---|---|
| 74Se | 73.922 4759(1) | 0.0086(3) | 0.0089(4) |
| 76Se | 75.919 2137(1) | 0.0923(7) | 0.0937(29) |
| 77Se | 76.919 9141(5) | 0.0760(7) | 0.0763(16) |
| 78Se | 77.917 309(1) | 0.2369(22) | 0.2377(28) |
| 80Se | 79.916 522(6) | 0.4980(36) | 0.4961(41) |
| 82Se | 81.916 699(3) | 0.0882(15) | 0.0873(22) |
| Nuclide | Atomic Mass and Uncertainty [u] | Half Life and Uncertainty | Discovery Year | Decay Modes, Intensities and Uncertainties [%] |
|---|---|---|---|---|
| 63Se | 62.981911 ± 0.000537 [Estimated] | 13.2 ms ± 3.9 | 2016 | β+=100%; β+p=89±1.1%; 2p<0.5% |
| 64Se | 63.971165 ± 0.000537 [Estimated] | 22.6 ms ± 0.2 | 2005 | β+ ?; β+p ? |
| 65Se | 64.964552 ± 0.000322 [Estimated] | 34.2 ms ± 0.7 | 1993 | β+=100%; β+p=87±1.3% |
| 66Se | 65.955276 ± 0.000215 [Estimated] | 54 ms ± 4 | 1993 | β+=100%; β+p ? |
| 67Se | 66.949994000 ± 0.000072 | 133 ms ± 4 | 1991 | β+=100%; β+p=0.5±0.1% |
| 68Se | 67.941825236 ± 0.000000532 | 35.5 s ± 0.7 | 1990 | β+=100% |
| 69Se | 68.939414845 ± 0.000001599 | 27.4 s ± 0.2 | 1974 | β+=100%; β+p=0.052±0.8% |
| 69Sem | 68.939414845 ± 0.000001599 | 2.0 us ± 0.2 | 1988 | IT=100% |
| 69Sen | 68.939414845 ± 0.000001599 | 955 ns ± 16 | 1988 | IT=100% |
| 70Se | 69.933515521 ± 0.0000017 | 41.1 m ± 0.3 | 1950 | β+=100% |
| 71Se | 70.932209431 ± 0.000003 | 4.74 m ± 0.05 | 1957 | β+=100% |
| 71Sem | 70.932209431 ± 0.000003 | 5.6 us ± 0.7 | 1982 | IT=100% |
| 71Sen | 70.932209431 ± 0.000003 | 19.0 us ± 0.5 | 1982 | IT=100% |
| 72Se | 71.927140506 ± 0.0000021 | 8.40 d ± 0.08 | 1948 | ε=100% |
| 73Se | 72.926754881 ± 0.000007969 | 7.15 h ± 0.09 | 1948 | β+=100% |
| 73Sem | 72.926754881 ± 0.000007969 | 39.8 m ± 1.7 | 1960 | IT=72.6±0.3%; β+=27.4±0.3% |
| 74Se | 73.922475933 ± 0.000000015 | Stable >2.3Ey | 1922 | IS=0.86±0.3%; 2β+ ? |
| 75Se | 74.922522870 ± 0.000000078 | 119.78 d ± 0.03 | 1947 | ε=100% |
| 76Se | 75.919213702 ± 0.000000017 | Stable | 1922 | IS=9.23±0.7% |
| 77Se | 76.919914150 ± 0.000000067 | Stable | 1922 | IS=7.60±0.7% |
| 77Sem | 76.919914150 ± 0.000000067 | 17.36 s ± 0.05 | 1947 | IT=100% |
| 78Se | 77.917309244 ± 0.000000191 | Stable | 1922 | IS=23.69±2.2% |
| 79Se | 78.918499252 ± 0.000000238 | 327 ky ± 28 | 1950 | β-=100% |
| 79Sem | 78.918499252 ± 0.000000238 | 3.900 m ± 0.018 | 1950 | IT≈100%; β-=0.056±1.1% |
| 80Se | 79.916521761 ± 0.000001016 | Stable | 1922 | IS=49.80±3.6%; 2β- ? |
| 81Se | 80.917993019 ± 0.000001049 | 18.45 m ± 0.12 | 1948 | β-=100% |
| 81Sem | 80.917993019 ± 0.000001049 | 57.28 m ± 0.02 | 1971 | IT≈100%; β-=0.051±1.4% |
| 82Se | 81.916699531 ± 0.0000005 | 87.6 Ey ± 1.5 | 1922 | IS=8.82±1.5%; 2β-=100% |
| 83Se | 82.919118604 ± 0.000003259 | 22.25 m ± 0.04 | 1937 | β-=100% |
| 83Sem | 82.919118604 ± 0.000003259 | 70.1 s ± 0.4 | 1969 | β-=100% |
| 84Se | 83.918466761 ± 0.000002105 | 3.26 m ± 0.10 | 1960 | β-=100% |
| 85Se | 84.922260758 ± 0.000002804 | 32.9 s ± 0.3 | 1960 | β-=100% |
| 86Se | 85.924311732 ± 0.000002705 | 14.3 s ± 0.3 | 1973 | β-=100%; β-n ? |
| 87Se | 86.928688616 ± 0.000002405 | 5.50 s ± 0.06 | 1968 | β-=100%; β-n=0.60±1.2% |
| 88Se | 87.931417490 ± 0.000003604 | 1.53 s ± 0.06 | 1970 | β-=100%; β-n=0.99±1% |
| 89Se | 88.936669058 ± 0.000004003 | 430 ms ± 50 | 1971 | β-=100%; β-n=7.8±2.5% |
| 90Se | 89.940096000 ± 0.000354 | 210 ms ± 80 | 1994 | β-=100%; β-n ? |
| 91Se | 90.945700000 ± 0.000465 | 270 ms ± 50 | 1975 | β-=100%; β-n=21±1%; β-2n ? |
| 92Se | 91.949840 ± 0.000429 [Estimated] | 90 ms >300ns [Estimated] | 1997 | β- ?; β-n ?; β-2n ? |
| 92Sem | 91.949840 ± 0.000429 [Estimated] | 15.7 us ± 0.7 | 2012 | IT=100% |
| 93Se | 92.956135 ± 0.000429 [Estimated] | 130 ms >300ns [Estimated] | 1997 | β- ?; β-n ?; β-2n ? |
| 93Sem | 92.956135 ± 0.000429 [Estimated] | 420 ns ± 100 | 2012 | IT=100% |
| 94Se | 93.960490 ± 0.000537 [Estimated] | 50 ms >300ns [Estimated] | 1997 | β- ?; β-n ?; β-2n ? |
| 94Sem | 93.960490 ± 0.000537 [Estimated] | 680 ns ± 50 | 2020 | IT=100% |
| 95Se | 94.967300 ± 0.000537 [Estimated] | 70 ms >400ns [Estimated] | 2010 | β- ?; β-n ?; β-2n ? |
