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Selenium (Se)

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

SymbolSe
Atomic number34
Group16
Period4
Blockp
Element categoryNonmetal

Physical properties

Phase at STPSolid
Density4.81 g/cm3
Atomic weight78.9718 u
Melting point494 K
220.85 °C
429.53 °F
Boiling point958 K
684.85 °C
1264.73 °F

Atomic properties

Electronegativity (Pauling Scale)2.55
Electron affinity194.959 kJ/mol
Oxidation states−2, −1, +1, +2, +3, +4, +5, +6
(a strongly acidic oxide)
Ionization energies
1941 kJ/mol
2 2045 kJ/mol
3 2973.7 kJ/mol
4 4144 kJ/mol
5 6590 kJ/mol
6 7880 kJ/mol
7 14990 kJ/mol

Electron configuration

Elektronkonfiguration (shorthand)[Ar] 3d10 4s2 4p4
Electron configuration1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4
Electrons per shell2, 8, 18, 6

History

Discovered1817
Discovered byJöns Jakob Berzelius
Johan Gottlieb Gahn
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