SELENIUM
CHALCOGENS ELEMENT
| Atomic number: | 34 |
| Group numbers: | 16 |
| Period: | 4 |
| Electronic configuration: | [Ar] 3d10 4s2 4p4 |
| Formal oxidation number: | -2 +4 +6 |
| Electronegativities: | 2.55 |
| Atomic radius / pm: | 116 |
| Relative atomic mass: | 78.971(8) |
Selenium was discovered by Jöns Jacob Berzelius (SE) in 1817. The origin of the name comes from the Greek word selene meaning moon. It is a soft metalloid similar to sulfur, unaffected by water and soluble in alkalis and nitric acid. The colour ranges from grey metallic to red glassy. Selenium burns in air and is toxic by inhalation or ingestion. Also it conducts electricity when struck by light. Selenium is obtained from lead, copper and nickel refining. Light causes it to conduct electricity more easily. It is used in photoelectric cells, TV cameras, xerography machines and as a semiconductor in solar batteries and rectifiers, also colours glass red. The price of 99.999 % pure amorphous selenium shot is 301.80 € for 1000 g.
| Density / g dm-3: | 4790 | (grey, 293 K) |
| 3987 | (m.p.) | |
| Molar volume / cm3mol-1: | 16.48 | (grey, 293 K) |
| 19.80 | (m.p.) | |
| Electrical resistivity / µΩcm: | 12 | (20 °C) |
| Thermal conductivity / W m-1K-1: | 2.04 |
| Melting point / °C: | 221 |
| Boiling point / °C: | 685 |
| Heat of fusion / kJ mol-1: | 5.1 |
| Heat of vaporization / kJ mol-1: | 90 |
| Heat of atomization / kJ mol-1: | 226.4 |
| First ionization energy / kJ mol-1: | 940.97 |
| Second ionization energy / kJ mol-1: | 2044.54 |
| Third ionization energy / kJ mol-1: | 2973.74 |
| in the atmosphere / ppm: | - |
| in the Earth's crust / ppm: | 0.05 |
| in the oceans / ppm: | - |
| Crystal structure: | hexagonal |
| Unit-cell dimensions / pm: | a=436.56, c=495.90 |
| Space group: | P3121 |
| Isotope | Relative atomic mass | Mass percent (%) |
|---|---|---|
| 74Se | 73.922477(2) | 0.89(2) |
| 76Se | 75.919214(2) | 9.36(11) |
| 77Se | 76.919915(2) | 7.63(6) |
| 78Se | 77.917310(2) | 23.78(9) |
| 80Se | 79.916522(2) | 49.61(10) |
| 82Se | 81.916700(2) | 8.73(6) |
| Balanced half-reaction | Eo / V | |
|---|---|---|
| SeO42- + 2H+ + 2e- → SeO32- + H2O | +0.880 | |
| SeO42- + H2O + 2e- → SeO32- + 2OH- | +0.05 | |
| SeO42- + 3H+ + 2e- → HSeO3- + H2O | +1.075 | |
| SeO42- + 4H+ + 2e- → H2SeO3 + H2O | +1.15 | |
| HSeO4- + 3H+ + 2e- → H2SeO3 + H2O | +1.090 | |
| SeO32- + 6H+ + 4e- → Se(s) + 3H2O | +0.875 | |
| HSeO3- + 5H+ + 4e- → Se(s) + 3H2O | +0.778 | |
| H2SeO3 + 4H+ + 4e- → Se(s) + 3H2O | +0.740 | |
| SeO32- + 6H+ + 6e- → Se2- + 3H2O | +0.276 | |
| SeO32- + 7H+ + 6e- → HSe- + 3H2O | +0.414 | |
| HSeO3- + 6H+ + 6e- → HSe- + 3H2O | +0.349 | |
| HSeO3- + 7H+ + 6e- → H2Se(g) + 3H2O | +0.386 | |
| H2SeO3 + 6H+ + 6e- → H2Se(g) + 3H2O | +0.360 | |
| Se(s) + 2H+ + 2e- → H2Se(g) | - 0.369 | |
| Se(s) + 2e- → Se2- | - 0.924 | |
| Se(s) + H+ + 2e- → HSe- | - 0.510 | |
| Se(s) + 2H+ + 2e- → H2Se(g) | - 0.399 |
| 33 Arsenic | ← | 34 Selenium | → | 35 Bromine |
Citing this page:
Generalic, Eni. "Selenium." EniG. Periodic Table of the Elements. KTF-Split, 13 Feb. 2025. Web. {Date of access}. <https://www.periodni.com/se.html>.
