• Class: Non-Metals
• Period: 4
• IUPAC group: 16
• Traditional: VIb

• Discovered in: 1817 by Berzelius
• Origin of name: Greek: Selene, (moon)
• Historical or alternate name:

Crooksite & clausthalite

Amorphous or crystaline red to grey solid. Unaffected by water. Soluble in alkalis and nitric acid. Burns in air.

• Atmosphere: ~0.0 ppm
• Primitive mantle: 0.041 ppm
• Sea water: ~0.0 ppm
• Metallic meteorite: 18.2 ppm
• Continental crust: 0.05 ppm
• Solar photosphere: ~0.0 log of abundance
• Oceanic crust: 0.160 ppm
• Solar system: 62.1 relative to Si=1.0e6

   Hazards

Poison. Toxic by inhalation or ingestion. Irritant by contact. Cumulative effects. Possible carcinogen..

• Lower:0.01
• Upper:1.0

Selenium Physical Properties

 Transitional Data

• State: Solid
• Density: 4.81 g/cm3

 Molar enthalpy

• Atomization: 226.40 kJ mol-1
• Fusion: 5.1 kJ mol-1
• Vaporization: 90 kJ mol-1

 Transition points

• Melting point: 490.0 K
• Boiling point: 958.0 K
• Critical temperature: 1757.0 K

 Molar properties

• Atomic weight: 78.96 g/mole
• Molar volume: 16.527 cm3 mol-1

 Crystal structure sequence

complex-trigonal <423 K < monoclinic < melting point

 Thermodynamics

• State: solid
  • Enthalpy 0
  • Gibbs function 0
  • Entropy 42.442
  • Heat Capacity 25.363

• State: gas
  • Enthalpy 227.07
  • Gibbs function 187.03
  • Entropy 176.72
  • Heat Capacity 20.820

 Miscellaneous physical

• Electrical resistivity: 12.0 µ-ohms/cm
• Debye temperature: 90.0 K
• Thermal conductivity: 2.04 W / m / K
• Coefficient of linear expansion: 45.8Coef. per K
• Mass magnetic susceptibility: -4.0e-9
• X-ray diffraction mass absorption coefficients:
• CuK: 91.4 (µ/p)/cm2 g-1
• MoK: 74.7 (µ/p)/cm2 g-1

Selenium Chemical Properties

 Chemical basics:

• Oxidation states: -2 +4 +6
• Molecular wt: 78.96 g/mole

 Radii

• Covalent: 117 pm
• Atomic: 117.0 pm
• Van der Waals: 200 pm

 Ions:

• ion: -2 pm 198.0
• ion: +4 pm 50.0
• ion: +6 pm 42.0

 Covalent bonds

 Effective nuclear charge

• Slater: 6.95
• Clementi: 8.29
• Froese-Fischer: 9.96

 Electronegativity

• Pauling: 2.4
• Allred-Rochow: 2.48

 Standard reactions

Selenium Nuclear Properties

• Known 20
• Listed 9

• Known 70 - 85
• Listed 72 - 82

• % Occ.:Natural
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life: 8.5 days
  • Decay mode: E.C.,
  • Source: reactor
• Notes

• % Occ.:Natural 0.9%
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life:
  • Decay mode:
  • Source:
• Notes

• % Occ.:Natural
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life: 120.0 days
  • Decay mode: E.C.,
  • Source: reactor
• Notes med

• % Occ.:Natural 9.0%
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life:
  • Decay mode:
  • Source:
• Notes

• % Occ.:Natural 7.6%
• Mossbauer NRA:
• Nuclear spin/Quantum no.: 1/2
• Radioisotopes:
  • Half-life:
  • Decay mode:
  • Source:
• Notes

• % Occ.:Natural 23.6%
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life:
  • Decay mode:
  • Source:
• Notes

• % Occ.:Natural
• Mossbauer NRA:
• Nuclear spin/Quantum no.: 7/2
• Radioisotopes:
  • Half-life: 650.0 centuries
  • Decay mode: Beta-
  • Source: reactor
• Notes

• % Occ.:Natural 49.7%
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life:
  • Decay mode:
  • Source:
• Notes

• % Occ.:Natural 9.2%
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life: 1.4 E20 years
  • Decay mode: Beta-Beta-
  • Source: reactor
• Notes

• Isotope Cross-section 12.2±0.6 barns

• Absolute sensitivity: 5.25e-4 1H=1.0
• Relative sensitivity: 6.93e-3 1H=1.0
• Receptivity: 2.98 13C=1.0
• Magnetogyric ratio: 5.1018e7 rad / T / s
• Quadropole moment: m2
• Frequency: 19.092 MHz
• Reference: S(CH3)2

Selenium Energy Properties

Electrons

• Ground state electron configuration: [Ar] 3d10 4s2 4p4
• Electron affinity: 195.0 kJ mol-1
• Filling orbitals:

Spectral lines

 Ionization energies

 Atomic energy levels