Selenium, Elemental

CAS RN:7782-49-2

Other Properties

Combines directly with hydrogen, with the halogens (excluding iodine); oxidized to selenious acid by nitric acid, to selenic acid by sulfuric acid; reduces hot aqueous soln of silver and gold salts with formation of silver selenide and metallic gold, respectively
Exhibits both photovoltaic action, where light is converted directly to electricity; exhibits photoconductive action, where electrical resistance decreases with increased illumination
Vitreous, Black selenium; dark red-brown to bluish-black solid; density = 4.28; softens at 50 to 60 deg C and becomes elastic at 70 deg C. Red amorphous form; density = 4.26. When freshly precipitated, reacts with water at 50 deg C forming selenious acid and hydrogen. Soluble in carbon disulfide, methylene iodide, benzene or quinoline /amorphous forms/
Two monoclinic forms; dark red, transparent crystals. Melting point below 200 deg C. Density (alpha-form) 4.46. Both forms are metastable and change into gray form on heating /Crystalline or red selenium/.
Crystalline selenium is a p-type semiconductor... forms binary alloys with silver, copper, zinc, lead, etc.
Selenium reacts with electropositive elements (many metals) to form selenides.
Liquid is a brownish red
Lustrous gray to black hexagonal crystals; insoluble in alcohol; very slightly soluble in carbon disulfide (2 mg/100 mL at ordinary temperature); soluble in ether; conducts electricity and rectifies alternating current; conductivity increases up to 1000 times on exposure to light; density 4.81 at 20 deg C/4 deg C; melting point 217 deg C; Mohs' hardness: 2.0; Latent heat of fusion 16.4 cal/g; Latent heat of vaporization 20.6 kcal/mol; Linear coefficient of thermal expansion per degree C = 37X10-6; Specific heat (28 deg C): 0.084 cal/g/deg C; Surface tension (217 deg C): 92.5 dynes/cm; Thermal conductivity (25 deg C): 0.0007-0.00183 cal/(cm)(deg C)sec. /Gray or metallic selenium/
Molar heat of fusion: 6.69 kJ/mol /Selenium (gray)/
Insoluble in ethanol; slightly soluble in ether /alpha-form/
Slightly soluble in carbon disulfide /vitreous/
Magnetic susceptibility: -25x10-6 cu cm/mol
Specific heat capacity: 0.321 J/g-K; molar heat capacity: 25.363 J/mol-K
Standard molar enthalpy of formation: 0.0 kJ/mol (gray), 6.7 kJ/mol (alpha form), 5.0 kJ/mol (vitreous); standard molar entropy: 42.4 J/mol-K (gray); molar heat capacity at constant pressure: 25.4 J/mol-K (gray)
Permittivity (dielectric constant): 5.44 at 510.65 K
Electron affinity: 2.020670 eV
Ionization energy: 9.75238 eV
Very salty solution in ether; viscosity decreases with temperature
Electronegativity, Pauling scale: 2.4
Selenium combines with oxygen to form several substances that are white or colorless crystals; some selenium compounds are gases
... selenates are easily reduced to selenium. /Selenium/
Selenium Decay Pathways
Natural Isotopes

Isotope Relative % Abundance Half-life Mode of Decay Decay energy
Selenium-74 0.89 Stable
Selenium-76 9.36 Stable
Selenium-77 7.63 Stable
Selenium-78 23.78 Stable
Selenium-80 49.61 Stable
Selenium-82 8.73 1.08X10+20(+26-6) years 2 Beta to Krypton-82 2.995 MeV
Selenium Decay Pathways
Artificial Isotopes

Isotope Half-life Mode of Decay Decay Energy (MeV)
Selenium-65 <50 milli seconds electron capture to As-65 14.100
Selenium-66 >1.2 micro seconds electron capture to As-66 1.100
Selenium-67 60 milli seconds electron capture to AS-67 7.840
Selenium-68 35.5 seconds electron capture to AS-68 4.700
Selenium-69 27.4 seconds electron capture to AS-69 6.780
electron capture + proton to Ge-68 3.390
Selenium-70 41.1 minutes electron capture to AS-70 2.400
Selenium-71 4.74 minutes electron capture to AS-71 4.800
Selenium-72 8.40 days electron capture to AS-72 0.335
Selenium-73 7.15 hrs electron capture to AS-73 2.740
Selenium-75 119.79 days electron capture to AS-75 0.864
Selenium-79 <= 650,000 years beta to Br-79 0.151
Selenium-81 18.45 minutes beta to Br-81 1.585
Selenium-83 22.3 minutes beta to Br-83 3.668
Selenium-84 3.10 minutes beta to Br-84 1.830
Selenium-85 31.7 seconds beta to Br-85 6.182
Selenium-86 15.3 seconds beta to Br-86 5.099
Selenium-87 5.29 seconds beta to Br-87 7.280
beta + neutron to Br-86 0.990
Selenium-88 1.53 seconds beta to Br-88 6.850
beta + neutron to Br-87 1.910
Selenium-89 0.41 seconds beta to Br-89 9.000
beta + neutron to Br-88 3.100
Selenium-90 >150 nanoseconds
Selenium-91 0.27 seconds beta to Br-91 10.700
beta + neutron to Br-90 5.700
Selenium-92 >150 nanoseconds beta to Br-92 9.400
Find more information on this substance at: Hazardous Substances Data Bank , TOXNET , PubMed