Selenium (Se)
Selenium (Se) is element 34, a nonmetal. Atomic mass 78.971, configuration [Ar] 3d¹⁰ 4s² 4p⁴. Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 34 |
|---|---|
| Symbol | Se |
| Standard atomic weight | 78.971(8) |
| Category | Other nonmetal |
| Group | 16 |
| Period | 4 |
| State at room temperature | Solid |
| Electron configuration | [Ar] 3d¹⁰ 4s² 4p⁴ |
| Valence electrons | 6 |
| Common oxidation states | -2, +2, +4, +6 |
| Common ions | No common ions |
| Electronegativity (Pauling) | 2.55 |
| First ionization energy | 941 kJ/mol |
| Electron affinity | 195 kJ/mol |
| Atomic radius | 103 pm |
| Density | 4.809 g/cm³ |
| Melting point | 221.1°C |
| Boiling point | 685°C |
| Specific heat | 0.321 J/(g·°C) |
Natural isotopes
- Se-74: Stable
- Se-76: Stable
- Se-77: Stable
- Se-78: Stable
- Se-80: Stable
- Se-82: Stable
Common uses
- Photocopying
- Glass decolorizing
- Solar cells
Where it matters
- Xerox process (Photoconductivity)
- Biological trace element
Hazards
- Toxic in large amounts
- essential in trace amounts
History
| Discovered | 1817 |
|---|---|
| Discovered by | Jöns Jakob Berzelius |
| Name | From Greek selene (Moon) |