Selenium
A light-sensitive nonmetal and essential trace nutrient.
Inside the Selenium atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Selenium atom step by step.
Electron configuration
[Ar] 3d10 4s2 4p4
A neutral Selenium atom has 34 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 494 K (221 °C)
- Boiling point
- 958 K (685 °C)
- Density
- 4.809 g/cm³
- Electronegativity
- 2.55 Pauling
- Atomic radius
- 115 pm
- 1st ionization energy
- 941 kJ/mol
- Category
- Reactive nonmetals
Discovery & naming
- Discovered
- 1817
- Discovered by
- Jöns Jacob Berzelius
- Origin of name
- Greek 'selene', the Moon.
Notable uses
Solar cells, glassmaking, and photocopiers.
Where Selenium comes from
Several comparable sources
Both slow neutron capture in dying stars and rapid capture in explosive events contribute meaningfully.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 34
- Atomic mass
- 78.971
- Category
- Reactive nonmetals
- Group · Period
- 16 · 4
- Block
- p-block
- Shells
- 2 · 8 · 18 · 6