| Selenium | |
| Electrons per shell | 2,8,18,6 |
| Electron Configuration | [Ar] 3d10 4s2 4p4 |
| 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)  |
|
| 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° | |