34SeSelenium78.9718[Ar] 3d¹⁰ 4s² 4p⁴
polyatomic nonmetal
Selenium
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.
A stylized shell model. Electrons are quantum objects, not particles following these literal paths. Sizes and motion are illustrative.
Electrons by shell
Electron configuration
3d10
4s2
4p4
18 is the [Ar] core total across three shells.
At a glance
- Atomic number
- 34
- Atomic mass
- 78.9718 u
- Phase
- Solid
- Density
- 4.81 g/cm³
- Melting point
- 494 K
- Boiling point
- 958 K
- First ionization energy
- 941 kJ/mol
- Electronegativity
- 2.55
- Electron affinity
- 194.9587 kJ/mol
- Molar heat capacity
- 25.363 J/(mol·K)
- Period
- 4
- Appearance
- black, red, and gray (not pictured) allotropes
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.