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Selenium (Se)

Selenium (Se) is element 34 of the periodic table, a nonmetal in period 4 and group 16. Its standard atomic weight is 78.971, so one mole of selenium atoms has a mass of 78.971 g. At room temperature it is a solid; it melts at 220.5 °C and boils at 684.85 °C.

34 Se Selenium 78.971

Period 4, group 16 · Nonmetal

← As Arsenic Br Bromine →

Atomic number	34
Symbol	Se
Standard atomic weight	78.971
Molar mass	78.971 g/mol
Category	Nonmetal
Group	16
Period	4
Block	p-block
Electron configuration	[Ar] 4s² 3d¹⁰ 4p⁴
Oxidation states	+6, +4, −2
Electronegativity (Pauling)	2.55
Atomic radius (van der Waals)	190 pm
First ionisation energy	9.752 eV (940.9 kJ/mol)
Electron affinity	2.021 eV
State at room temperature	Solid
Melting point	493.65 K (220.5 °C)
Boiling point	958 K (684.85 °C)
Density	4.809 g/cm³
Discovered	1817

Group 16

O · Oxygen S · Sulfur Te · Tellurium Po · Polonium Lv · Livermorium

Calculate with Selenium

Molar mass of Se Balance an equation Grams, moles and particles Whole periodic table

Atomic weight: IUPAC CIAAW standard atomic weight. Other properties: PubChem (U.S. National Library of Medicine, public domain). Values such as melting point and radius depend on how they were measured; check a data book for precise work.