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|
Selenium
Chemical Properties & Compounds
| Symbol | Atomic Number | Atomic Weight | Melting Point | Boiling Point | Phase | Density | Classification |
| Se | 34 | 78.96 | 221 °C | 685 °C | Solid | 4.809 g/cm3 | Non-Metal  |
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|
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| General |
| Name, Symbol, Number |
selenium, Se, 34 |
| Chemical series |
nonmetals |
| Group, Period, Block |
16, 4, p |
| Appearance |
gray-black, metallic luster
 |
| Standard atomic weight |
78.96(3) g·mol−1 |
| Electron configuration |
[Ar] 3d10 4s2 4p4 |
| Electrons per shell |
2, 8, 18, 6 |
| Physical properties |
| Phase |
solid |
| Density (near r.t.) |
(gray) 4.81 g·cm−3 |
| Density (near r.t.) |
(alpha) 4.39 g·cm−3 |
| Density (near r.t.) |
(vitreous) 4.28 g·cm−3 |
| Liquid density at m.p. |
3.99 g·cm−3 |
| Melting point |
494 K
(221 °C, 430 °F) |
| Boiling point |
958 K
(685 °C, 1265 °F) |
| Critical point |
1766 K, 27.2 MPa |
| Heat of fusion |
(gray) 6.69 kJ·mol−1 |
| Heat of vaporization |
95.48 kJ·mol−1 |
| Heat capacity |
(25 °C) 25.363 J·mol−1·K−1 |
Vapor pressure
| P(Pa) |
1 |
10 |
100 |
1 k |
10 k |
100 k |
| at T(K) |
500 |
552 |
617 |
704 |
813 |
958 |
|
| Atomic properties |
| Crystal structure |
hexagonal |
| Oxidation states |
±2, 4, 6
(strongly acidic oxide) |
| Electronegativity |
2.55 (scale Pauling) |
Ionization energies
(more) |
1st: 941.0 kJ·mol−1 |
| 2nd: 2045 kJ·mol−1 |
| 3rd: 2973.7 kJ·mol−1 |
| Atomic radius |
115 pm |
| Atomic radius (calc.) |
103 pm |
| Covalent radius |
116 pm |
| Van der Waals radius |
190 pm |
| Miscellaneous |
| Magnetic ordering |
no data |
| Thermal conductivity |
(300 K) (amorphous)
0.519 W·m−1·K−1 |
| Thermal expansion |
(25 °C) (amorphous)
37 µm·m−1·K−1 |
| Speed of sound (thin rod) |
(20 °C) 3350 m/s |
| Young's modulus |
10 GPa |
| Shear modulus |
3.7 GPa |
| Bulk modulus |
8.3 GPa |
| Poisson ratio |
0.33 |
| Mohs hardness |
2.0 |
| Brinell hardness |
736 MPa |
| CAS registry number |
7782-49-2 |
| Selected isotopes |
|
|
| References |
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Selenium Compounds
|
Source: Wikipedia article Selenium
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Chemistry Quick Facts
