From Wikipedia, the free encyclopediaSelenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between those of its periodic table column-adjacent chalcogen elements sulfur and tellurium. It rarely occurs in its elemental state in nature, or as pure ore compounds. | |||||||||||||||
Selenium in the periodic table | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Symbol | Se | ||||||||||||||
Atomic number | 34 | ||||||||||||||
Group | 16 | ||||||||||||||
Period | 4 | ||||||||||||||
Block | p | ||||||||||||||
Element category | Nonmetal | ||||||||||||||
Physical properties | |||||||||||||||
Phase at STP | Solid | ||||||||||||||
Density | 4.81 g/cm3 | ||||||||||||||
Atomic weight | 78.9718 u | ||||||||||||||
Melting point | 494 K 220.85 °C 429.53 °F | ||||||||||||||
Boiling point | 958 K 684.85 °C 1264.73 °F | ||||||||||||||
Atomic properties | |||||||||||||||
Electronegativity (Pauling Scale) | 2.55 | ||||||||||||||
Electron affinity | 194.959 kJ/mol | ||||||||||||||
Oxidation states | −2, −1, +1, +2, +3, +4, +5, +6 (a strongly acidic oxide) | ||||||||||||||
Ionization energies |
| ||||||||||||||
Electron configuration | |||||||||||||||
Elektronkonfiguration (shorthand) | [Ar] 3d10 4s2 4p4 | ||||||||||||||
Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 | ||||||||||||||
Electrons per shell | 2, 8, 18, 6 | ||||||||||||||
History | |||||||||||||||
Discovered | 1817 | ||||||||||||||
Discovered by | Jöns Jakob Berzelius Johan Gottlieb Gahn |