Selenium (Se)
Reactive nonmetal · p-block · period 4 · group 16
Grey metallic-looking form, or a brick-red powder.
Selenium (symbol Se) is chemical element number 34, a reactive nonmetal in group 16, period 4 of the periodic table. Its standard atomic weight is 78.971 and its electron configuration is [Ar] 3d10 4s2 4p4. At room temperature it is a solid. Its electrical resistance drops in light, which made the first photocopiers and light meters work.
Properties
| Atomic number | 34 |
|---|---|
| Atomic mass | 78.971 |
| Category | Reactive nonmetal |
| Block | p-block |
| Group · Period | 16 · 4 |
| Electron configuration | [Ar] 3d10 4s2 4p4 |
| Electrons per shell | 2, 8, 18, 6 |
| State at 25 °C | solid |
| Melting point | 494 K |
| Boiling point | 958 K |
| Density | 4.81 g/cm³ |
| Electronegativity (Pauling) | 2.55 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1817 · Jöns Jacob Berzelius |
Key facts about Selenium
- Its electrical resistance drops in light, which made the first photocopiers and light meters work.
- Named after Selene, the Greek Moon goddess.
- An essential trace nutrient, but toxic in only slightly larger amounts.
- Gives a brilliant red colour to glass and ceramic glazes.
What Selenium is used for
Anti-dandruff shampoo, glass decolourising and red glass, photocells, dietary supplements, electronics.
Where it sits in the periodic table
Selenium is in group 16, period 4, of the p-block. Its electron configuration [Ar] 3d10 4s2 4p4 means its outermost shell holds 6 electrons, which is what places it here and explains much of its chemistry. See Selenium on the interactive table →
Selenium — frequently asked questions
What is Selenium used for?
Anti-dandruff shampoo, glass decolourising and red glass, photocells, dietary supplements, electronics.
Is Selenium radioactive?
No. Selenium has at least one stable isotope and is not radioactive.
What is the electron configuration of Selenium?
Selenium has the electron configuration [Ar] 3d10 4s2 4p4, which is 2, 8, 18, 6 electrons per shell.
What group and period is Selenium in?
Selenium is in group 16, period 4, in the p-block. Its outer shell holds 6 electrons.
Who discovered Selenium?
Selenium was discovered in 1817 by Jöns Jacob Berzelius.