Selenium (Se)
Element 34 · Reactive nonmetal
Selenium (Se) is a chemical element with atomic number 34. It is classified as a reactive nonmetal in period 4, group 16 of the periodic table (the p-block). Its standard atomic weight is 78.971 u and its ground-state electron configuration is [Ar] 3d¹⁰ 4s² 4p⁴.
Selenium facts
| Atomic number (Z) | 34 |
|---|---|
| Symbol | Se |
| Standard atomic weight | 78.971 u |
| Category | Reactive nonmetal |
| Group | 16 |
| Period | 4 |
| Block | p-block |
| Electron configuration | [Ar] 3d¹⁰ 4s² 4p⁴ |
| Electronegativity (Pauling) | 2.55 |
| State at 20 °C | Solid |
| Protons / electrons | 34 / 34 |
| Neutrons (most common isotope, approx.) | 45 |
| Molar mass | 78.971 g/mol |