Se
Selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It has a standard atomic weight of 78.971, sits in period 4 and group 16, and is classified as a reactive nonmetal.
Properties
| Symbol | Se |
|---|---|
| Atomic number | 34 |
| Standard atomic weight | 78.971 |
| Category | Reactive nonmetal |
| Group | 16 |
| Period | 4 |
| Electron configuration | [Ar] 3d10 4s2 4p4 |
| Outer-shell electrons | 6 |
The figure of 78.971 is a standard atomic weight.
Calculate with selenium
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Group 16
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.