Relative atomic mass: 78.96 +- 0.03

English: Selenium
French: Selenium
Croatian: Selenij
German: Selen
Italian: Selenio
Spanish: Selenio

Atomic number: 34
Group numbers: 16
Period: 4
Standard state (20 oC): solid

Discovery: 1817 Jons Jacob Berzelius (SE)
Selenium was discovered by Jons 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.
Electronic configuration: [Ar] 3d10 4s2 4p4
Formal oxidation number: -2 +4 +6
Atomic radius: 116 pm

Electronegativities: 2.55
Thermal conductivity: 2.04 W/(m K)
Electrical resistivity (20 oC): 12 microOhm cm

Melting point: 221 oC
Boiling point: 685 oC

Heat of fusion: 5.1 kJ/mol
Heat of vaporization: 90 kJ/mol
Heat of atomization: 226.4 kJ/mol

33As <= 34Se => 35Br

ASCII Periodic Table of the Elements
6 Jan. 2020
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