34Se78.97
Selenium
Nonmetal
Solid at STP
Period 4Group 16Block PDiscovered 1817
[Ar]4s2 3d10 4p4
Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between those of its periodic table column-adjacent chalcogen elements sulfur and tellurium. It rarely occurs in its elemental state in nature, or as pure ore compounds.
📖 Read more on Wikipedia →Atomic Properties
| Atomic Number | 34 |
| Atomic Mass | 78.97 u |
| Electron Configuration | [Ar]4s2 3d10 4p4 |
| Oxidation States | +6, +4, -2 |
| Electronegativity | 2.55 (Pauling) |
| Atomic Radius | 190 pm |
| Ionization Energy | 9.752 eV |
| Electron Affinity | 2.021 eV |
| Block | P |
Physical Properties
| Appearance | black, red, and gray (not pictured) allotropes |
| Standard State | Solid |
| Melting Point | 493.65 K (220.5 °C) |
| Boiling Point | 958 K (684.9 °C) |
| Density | 4.809 g/cm³ |
| Molar Heat | 25.363 J/(mol·K) |
| CPK Color | #FFA100 |
Classification
| Category | Nonmetal |
| Group Block | Nonmetal |
| Period | 4 |
| Group | 16 |
| Block | P |
Discovery
| Year Discovered | 1817 |
| Discovered By | Jöns Jakob Berzelius |
| Electron Shells | 2, 8, 18, 6 |