Se
Selenium is an essential trace element used in electronics and dietary supplements.
Physical Properties
| Atomic Mass | 78.971 u |
| Density | 4.809 g/cm³ |
| Melting Point | 494.0 K |
| Boiling Point | 958.0 K |
| Appearance | Red to gray, black in vitreous form |
| State at Room Temp | Solid |
Chemical Properties
| Electronegativity | 2.55 (Pauling) |
| 1st Ionization Energy | 941.0 kJ/mol |
| Electron Affinity | 195.0 kJ/mol |
| Oxidation States | -2, +2, +4, +6 |
Atomic Properties
| Electron Configuration | [Ar] 3d10 4s2 4p4 |
| Atomic Radius | 103.0 pm |
| Covalent Radius | 120.0 pm |
| Van der Waals Radius | 190.0 pm |
Discovery
| Discovered By | Jons Jacob Berzelius |
| Discovery Year | 1817 |
| Location | Stockholm, Sweden |
| Named After | Greek 'selene' meaning moon |
About Selenium
Selenium has properties between sulfur and tellurium. Its conductivity changes with light, making it useful in photoconductors. It is an essential trace element as a component of selenocysteine.
Uses & Applications
Photovoltaic cells, photocopiers, glass manufacturing, dietary supplements, and semiconductors.
Fun Fact
Selenium is essential in tiny amounts but toxic in larger doses. Brazil nuts are the richest known dietary source.
Isotopes
| Mass Number | Abundance | Half-Life | Stable |
| 76 | 0.0937% | - | Yes |
| 78 | 0.2377% | - | Yes |
| 80 | 0.4961% | - | Yes |
| 82 | 0.0873% | - | Yes |
Electron Configuration
[Ar] 3d10 4s2 4p4