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Selenium
Reactive nonmetals · Group 16 · Period 4
Atomic properties
| Atomic number | 34 |
|---|---|
| Symbol | Se |
| Standard atomic weight | 78.971 |
| Classification | Reactive nonmetals |
| Group | 16 |
| Period | 4 |
| Block | p-block |
| Electron configuration | [Ar] 3d10 4s2 4p4 |
| Electronegativity (Pauling) | 2.55 |
| Common oxidation states | +6, +4, -2 |
Physical properties
| Phase at 20 °C | Solid |
|---|---|
| Density | 4.81 g/cm³ |
| Melting point | 221 °C |
| Boiling point | 685 °C |
| Discovered | 1817 |
| CAS number | — |