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Atomic: M.A.C. | Reference
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Selenium
Electrons per shell 2,8,18,6
Electron Configuration [Ar] 3d10 4s2 4p4 open electron config
Ground state 3P2
Atomic Volume 16.45 cm3 mol-1
Electronegativity 2.55
Magnetic ordering No data
Mass magnetic susceptibility -4 x 10-9
Molar magnetic susceptibility -3.16 x 10-10
Speed of sound 3350 m s-1
Thermal Properties
Enthalpy of Atomization 205.9 kJ mol-1 @25°C
Enthalpy of Fusion 5.1 kJ mol-1
Enthalpy of Vaporisation 90 kJ mol-1
Heat Capacity 25.363 J mol-1 K-1
Thermal Conductivity 0.519 W m-1 K-1
Thermal Expansion 37 μm m-1 K-1
Hardness
Brinell hardness 736 MPa
Mohs hardness 2.0
Elastic Properties
Bulk modulus 8.3 GPa
Poisson ratio 0.33
Shear modulus 3.7 GPa
Young's modulus 10 GPa
Electrical Properties
Electrical resistivity No data.
Electrical conductivity 1 x 10-12 106/cm Ω
Chemical Properties
Electrochemical Equivalent 0.7365 g Ah-1
Electron Work Function 5.9 eV
Valence Electron Potential (-eV) 120
Ionization Potential  
First 9.752
Second 21.19
Third 30.82
Incompatibilities Acids, strong oxidizers, chromium trioxide (CrO3), potassium bromate (BrKO3), cadmium.
Flammability
Combustible Solid
Optical Properties
Refractive Index (gas) 1.000895
Energy Levels
Kα1 (intensity 100) 11.2224 KeV
Kα2 (intensity 50) 11.1814 KeV
Kβ1 (intensity 15) 12.4959 KeV
Kβ2 (intensity 2) 12.6504 KeV
Kβ3 (intensity 7.5) 12.4869 KeV
Lα1 (intensity 100) 1.3791 KeV
Lα2 (intensity 10) 1.3791 KeV
Lβ1 (intensity 34.1) 1.41923 KeV
Lβ3 (intensity 0.2) 1.489 KeV
Lβ4 (intensity 0.2) 1.49 KeV
Lγ3 (intensity 3) 1.244 KeV
Ll (intensity 7) 1.2061 KeV
Atomic Radii
Empirical 115 pm
Bohr Radius 103 pm
Covalent Radius 116 pm
Van der Waals 190 pm
Triple covalent 107 pm
Metallic No data.
Oxidation States
Main Se+4, Se+6
Other Se-2, Se+1, Se+2
Ionisation Energies (kJ mol-1) show graph
M - M+ 940.9
M+ - M2+ 2044
M2+ - M3+ 2974
M3+ - M4+ 4144
M4+ - M5+ 6590
M5+ - M6+ 7883
M6+ - M7+ 14990
M7+ - M8+ 19500
M8+ - M9+ 23300
M9+ - M10+ 27200
Covalent Bonds (kJ mol-1)
Se-H 305
Se-C 245
Se-O 343
Se-F 285
Se-Cl 245
Se-Se 330
Vapour Pressure
P (Pa) 1 10 100 1K 10K 100K
T (K) 500 552 617 704 813 958
Crystal Structure
Structure Monoclinic
a = 905.4 pm
b = 908.3 pm
c = 1160.1 pm
α = 90°
β = 90.810°
γ = 90°