Selenium

Symbol	Se
Latin name	Selenium
Atomic number	34
Period	4
Element category	Nonmetals
Relative atomic mass	78.96
Group	VI.A
Electronegativity	2.4
Oxidation numbers	-2, 2, 4, 6
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴
Density [g/cm³]	4.80
State	Solid
Melting point [°C]	217
Boiling point [°C]	685
Critical point [°C]	1493
Critical pressure [MPa]	27.2
Thermal conductivity [W m^-1K^-1]	2.04
Heat capacity [J K^-1g^-1]	0.32
Discovery	1817
Hardness [Mohs scale]	2.0
Brinell hardness [MPa]	736
Young's modulus [GPa]	10
Electrical conductivity [S m^-1]	8 · 10⁶
Shear modulus [GPa]	3.7
1.st ionization energy [eV]	9.7524
2.nd ionization energy [eV]	21.19
3.rd ionization energy [eV]	30.82
Stable isotopes	6
Unstable isotopes	14