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34Se78.972
Selenium
Polyatomic NonmetalSelenium 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.
Phase: SolidAppearance: black, red, and gray (not pictured) allotropes
2, 8, 18, 6
Physical Properties
Atomic Mass78.9718 u
Density4.81 g/cm³
Melting Point494 K
Boiling Point958 K
Molar Heat25.363 J/(mol·K)
Period4
PhaseSolid
Chemical Properties
Electron Configuration1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
Semantic Config[Ar] 3d10 4s2 4p4
Shells2, 8, 18, 6
Electron Affinity194.9587 kJ/mol
Electronegativity2.55
Ionization Energies
IE1: 941 kJ/molIE2: 2045 kJ/molIE3: 2973.7 kJ/molIE4: 4144 kJ/molIE5: 6590 kJ/molIE6: 7880 kJ/molIE7: 14990 kJ/mol
Discovery
Discovered byJöns Jakob Berzelius