Nuclides
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Chemical element · Atomic number 34
Selenium (Se)
Other nonmetals · Period 4 · Solid
Element identity
- Atomic number (Z)
- 34
- Symbol
- Se
- Atomic weight / isotope mass number
- 78.971(8)
- Category
- Other nonmetals
- Physical state (reference)
- Solid
- Period
- 4
- Group (reference)
- 16
- Block
- p
Physical properties
- Appearance
- Black, red, and gray allotropes
- Density
- Alpha: 4.39 g·cm⁻³ Gray: 4.81 g·cm⁻³ Vitreous: 4.28 g·cm⁻³
- Melting point
- 494 K / 221 °C / 430 °F
- Boiling point
- 958 K / 685 °C / 1265 °F
- Sublimation point
- Not available
Atomic and material properties
- Electron configuration
- [Ar] 3d¹⁰ 4s² 4p⁴
- Electrons per shell
- K2 L8 M18 N6
- Oxidation states
- 6, 5, 4, 3, 2, 1, −1, −2
- Electronegativity (Pauling)
- 2.55
- Atomic radius
- 103 pm
- Covalent radius
- 120±4 pm
- Molar ionization energies
- 1st: 941.0 kJ·mol⁻¹ 2nd: 2045 kJ·mol⁻¹ 3rd: 2973.7 kJ·mol⁻¹ 4th: 4144 kJ·mol⁻¹ 5th: 6590 kJ·mol⁻¹ 6th: 7880 kJ·mol⁻¹ 7th: 14,990 kJ·mol⁻¹
- Thermal conductivity
- Amorphous: 0.519 W·m⁻¹·K⁻¹
- Molar heat capacity
- 25.363 J·mol⁻¹·K⁻¹
- Crystal structure
- Hexagonal
- CAS number
- 7782-49-2
Property source: Wikipedia — Selenium, adapted from the Nuclides App snapshot. Quoted conditions and qualifiers are retained.
Sources and interpretation
Snapshot exported 24 October 2026 from the element assets used by Nuclides. Properties are a reference compilation, not a new evaluation. Missing values are shown as “Not available”. Density and phase depend on temperature, pressure and allotrope; retained conditions are part of the quoted property.
Atomic weight is dimensionless. Parentheses give uncertainty in the last quoted digits. A single integer in square brackets is an isotope mass number, not a standard atomic weight. The snapshot can differ from current evaluations; consult CIAAW standard atomic weights and the IUPAC periodic table for current values and conventions.
Element properties in the App snapshot are adapted from Wikipedia. Each element page links to its source article; text adaptations are available under CC BY-SA 4.0. No third-party images are included.
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