Selenium (Se)
nonmetalSolid
Standard Atomic Weight
78.971 uElectron configuration
[Ar] 4s2 3d10 4p4Melting point
220.5 °CBoiling point
684.85 °CDensity
4809 kg/m³Oxidation states
−2, −1, 0, +1, +2, +3, +4, +5, +6Electronegativity (Pauling)
2.55Ionization energy (1st)
9.752368 eVDiscovery year
1817Atomic radius
115 pmDetails
Selenium is a chalcogen between sulfur and tellurium, with chemistry that commonly parallels both. It is a trace element required by many organisms because it is incorporated into selenoproteins, yet the margin between nutritional requirement and toxicity is narrow. Industrially, selenium is valued for its semiconductor and photoconductive behavior, its red color in glass, and its role in metallurgy and specialty chemicals.
Selenium exists in several allotropic forms, although three are generally recognized. Selenium can be prepared with either an amorphous or a crystalline structure. The color of amorphous selenium is either red (in powder form) or black (in vitreous form). Crystalline monoclinic selenium is a deep red; crystalline hexagonal selenium, the most stable variety, is a metallic gray.
Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for photographic use, as well as solar cells. Selenium is also able to convert a.c. electricity to d.c., and is extensively used in rectifiers. Below its melting point, selenium is a p-type semiconductor and has many uses in electronic and solid-state applications.
Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element; however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions.
The name derives from the Greek Selene, who was the Greek goddess of the Moon because the element is chemically found with tellurium (Tellus was the Roman goddess of the Earth). Selenium was discovered by the Swedish chemist Jöns Jacob Berzelius in 1817, while trying to isolate tellurium in an impure sample.
Selenium was discovered by Jöns Jacob Berzelius, a Swedish chemist, in 1817 after analyzing an impurity that was contaminating the sulfuric acid (H2SO4) being produced at a particular factory in Sweden. Originally believing the material was tellurium, Berzelius eventually realized that it was actually a previously unknown element. Selenium occurs in minerals such as eucairite (CuAgSe), crooksite (CuThSe) and clausthalite (PbSe), but these minerals are too rare to use as a major source of selenium. Today, most selenium is obtained as a byproduct of refining copper.
From the Greek word Selene, moon. Discovered by Berzelius in 1817, who found it associated with tellurium (named for the earth).
Elemental selenium has several allotropes. The most familiar macroscopic forms are red amorphous selenium and gray trigonal selenium, a brittle, metallic-looking solid that is the most stable form at ordinary conditions. Black vitreous selenium can form by rapid cooling from the melt.
Selenium has been used in photocells, light meters, rectifiers, and xerographic photoreceptors, although many of these applications have been reduced by silicon and organic photoconductors. It is still used to decolorize or color glass, producing ruby-red glasses and counteracting green iron tints. Small additions improve machinability in some copper and steel alloys. Selenium compounds are used in pigments, rubber vulcanization chemistry, antifungal shampoos, and as reagents in organic synthesis.
Selenium's resistance to the flow of electricity is greatly affected by the amount of light shining on it. The brighter the light, the better selenium conducts electricity. This property has made selenium useful in devices that respond to the intensity of light, such as electric eyes, photo cells, light meters for cameras and copiers. Selenium can also produce electricity directly from sunlight and is used in solar cells. Selenium is also a semiconductor and is used in some types of solid-state electronics as well as in rectifiers, devices which convert alternating current electricity into direct current electricity. In addition to its use in electrical devices, selenium is also used to make a ruby-red color in glasses and enamels, as a photographic toner and as an additive to stainless steel.
Selenium forms few inorganic compounds, none of which are commercially important. They include selenious acid (H2SeO3), selenium dichloride (SeCl2) and selenium oxychloride (SeOCl2).
Selenium is used in Xerography for reproducing and copying documents, letters, etc. It is used by the glass industry to decolorize glass and to make ruby-colored glasses and enamels. It is also used as a photographic toner, and as an additive to stainless steel.
Isotopes in Earth/Planetary Science
Molecules, atoms, and ions of the stable isotopes of selenium possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of selenium in natural terrestrial materials (Fig. IUPAC.34.1).
Isotopes in Industry
75Se (with a half-life of 120 days) is used for X-ray radiography of welds to visualize welds and ensure that each weld is appropriate for its purpose [274] P. Hayward, D. Currie. “Radiography of welds using seleniuim 75, Ir 192 and x-rays”, in Asia-Pacific Conference on NDT, Auckland, New Zealand (2006)..
Isotopes in Medicine
75Se-selenomethionine (organic compound that combines to form proteins, found in Brazil nuts and soybeans) has been used to study the production of digestive enzymes (biological catalysts that accelerates chemical reactions) [275] A. C. Colella, F. Pigorini. Br. J. Radiol.40, 662 (1967).. Selenium stable isotopes are used in metabolic studies to monitor selenium intake and output [276] C. A. Swanson, D. C. Reamer, C. Veillon, J. C. King, O. A. Levander. Am. J. Clin. Nutr.38, 169 (1983)., [277] Public Health Service Agency for Toxic Substances and Disease Registry. Toxicological Profile for Selenium, U.S. Department of Health and Human Services (2014), Feb. 26; http://www.atsdr.cdc.gov/ToxProfiles/tp92.pdf..
Isotopes Used as a Source of Radioactive Isotope(s)
77Se and 78Se are used to produce the therapeutic radioisotope 77Br via the 77Se (n, p) 77Br and the 78Se (n, 2p) 77Br reactions, respectively. 80Se is used to produce 80mBr via the reaction 80Se (n, p) 80mBr. The m the superscript of 80mBr indicates a metastable state of the isotope.
Selenium occurs in oxidation states from −2 to +6, with −2, +4, and +6 especially important. Hydrogen selenide, H₂Se, is a highly toxic gas and the selenium analogue of hydrogen sulfide. Selenium dioxide, SeO₂, is a useful oxidizing reagent and forms selenous acid, H₂SeO₃, in water. Selenates such as sodium selenate, Na₂SeO₄, resemble sulfates chemically but are biologically more active. Metal selenides are important semiconductors, including cadmium selenide, CdSe, and copper indium gallium selenide used in thin-film photovoltaics.
See more information at the Selenium compound page.
Selenium is essential in trace amounts, but excess intake can cause selenosis, with gastrointestinal effects, hair and nail changes, and a garlic-like breath odor from volatile metabolites. Elemental selenium is less acutely hazardous than many soluble selenite and selenate salts, but dust exposure should be controlled. Hydrogen selenide, H₂Se, is extremely poisonous, and industrial selenium fumes or aerosols require strict ventilation and monitoring.
Hydrogen selenide at a concentration of 1.5 ppm is intolerable to man. Selenium occurs in some solid in amounts sufficient to produce serious effects on animals feeding on plants, such as locoweed, grown in such soils. Exposure to selenium compounds (as Se) in air should not exceed 0.2 mg/m3 (8-hour time-weighted average - 40-hour week).
Selenium is widely dispersed in sulfide ores, sedimentary rocks, soils, and waters, usually at low concentrations. Weathering and irrigation can mobilize selenate and selenite, which are taken up by plants and can bioaccumulate in food webs. Some plants tolerate and concentrate selenium, while many others show toxicity only where soils or drainage waters are selenium-rich. Microorganisms can reduce soluble selenium species to less mobile elemental selenium or volatile methylated forms.
Selenium is not normally mined as a primary product. Most commercial supply is recovered as a by-product from anode slimes produced during electrolytic refining of copper, with smaller links to other nonferrous metal processing. Demand is spread across glass manufacture, metallurgy, chemicals, electronics, and thin-film photovoltaic materials, so supply depends strongly on copper refining rather than direct selenium ore availability. Substitution has reduced some older electrical uses, but recovery remains economically useful because selenium is concentrated in refinery residues. Recycling occurs mainly through industrial scrap and process residues rather than consumer products.
Obtained from lead, copper and nickel refining. Conducts electricity when struck by light.
Selenium is a relatively uncommon cosmic element compared with lighter chalcogens. Its stable isotopes are produced mainly by neutron-capture processes in evolved stars and supernova-related environments, with contributions from both slow and rapid neutron capture. In planetary materials it behaves partly as a chalcophile element, tending to associate with sulfides rather than silicate minerals.
- Gray selenium conducts electricity better when illuminated.
- Selenium can replace sulfur in some amino acids, forming selenocysteine and selenomethionine.
- The smell associated with selenium exposure often comes from volatile methylated selenium compounds.
- Selenium was identified in residues from sulfuric acid manufacture.
- Some selenium-rich plants can poison grazing animals on naturally seleniferous soils.
- Cadmium selenide quantum dots can emit size-tunable visible light.
Images
Properties
Physical
- Atomic radius (empirical)
- 115 pm Compare Atomic radius (empirical) of all elements →
- Covalent radius
- 120 pm Compare Covalent radius of all elements →
- Van der Waals radius
- 190 pm Compare Van der Waals radius of all elements →
- Metallic radius
- 117 pm Compare Metallic radius of all elements →
- Density
- 4809 kg/m³ Compare Density of all elements →
- Molar volume
- 0.0165 L/mol
- Phase at STP
- Solid Compare Phase at STP of all elements →
- Melting point
- 220.5 °C Compare Melting point of all elements →
- Boiling point
- 684.85 °C Compare Boiling point of all elements →
- Thermal conductivity
- 0.52 W/(m·K) Compare Thermal conductivity of all elements →
- Specific heat capacity
- 0.321 J/(g·K) Compare Specific heat capacity of all elements →
- Molar heat capacity
- 25.363 J/(mol·K) Compare Molar heat capacity of all elements →
- Crystal structure
- Hexagonal close-packed Compare Crystal structure of all elements →
Chemical
- Electronegativity (Pauling)
- 2.55 Compare Electronegativity (Pauling) of all elements →
- Electronegativity (Allen)
- 2.424
- Electron affinity
- 2.0206 eV
- Ionization energy (1st)
- 9.752368 eV Compare Ionization energy (1st) of all elements →
- Ionization energy (2nd)
- 21.196073 eV Compare Ionization energy (2nd) of all elements →
- Ionization energy (3rd)
- 31.697109 eV Compare Ionization energy (3rd) of all elements →
- Ionization energy (4th)
- 42.947148 eV Compare Ionization energy (4th) of all elements →
- Ionization energy (5th)
- 68.300235 eV Compare Ionization energy (5th) of all elements →
- Oxidation states
- −2, −1, 0, +1, +2, +3, +4, +5, +6 Compare Oxidation states of all elements →
- Valence electrons
- 6 Compare Valence electrons of all elements →
- Allotropes
- ["gray", "vitreous"]
- Electron configuration
- [Ar] 4s2 3d10 4p4
Thermodynamic
- Critical point (temperature)
- 1493 °C
- Heat of fusion
- 0.0693372 eV Compare Heat of fusion of all elements →
- Heat of vaporization
- 0.27258123 eV Compare Heat of vaporization of all elements →
- Heat of sublimation
- 2.352697 eV
- Heat of atomization
- 2.352697 eV
- Atomization enthalpy
- 2.35477 eV
Nuclear
- Protons
- 34 Compare Protons of all elements →
- Neutrons
- 46 Compare Neutrons of all elements →
- Known isotopes
- 33 Compare Known isotopes of all elements →
- Stable isotopes
- 4 Compare Stable isotopes of all elements →
- Most stable isotope
- Se-80
- Discovery year
- 1817
Abundance
- Abundance (Earth's crust)
- 0.05 mg/kg Compare Abundance (Earth's crust) of all elements →
- Abundance (ocean)
- 2 × 10−4 mg/L Compare Abundance (ocean) of all elements →
Crystal Structure
- Lattice constant a
- 436 pm
Electronic Structure
- Electrons per shell
- 2, 8, 18, 6 Compare Electrons per shell of all elements →
Identifiers
- CAS number
- 7782-49-2 Compare CAS number of all elements →
- Term symbol
- 3P2
- InChI
- InChI=1S/Se
- InChI Key
- BUGBHKTXTAQXES-UHFFFAOYSA-N
Electron Configuration Measured
Se: 3d¹⁰ 4s² 4p⁴[Ar] 3d¹⁰ 4s² 4p⁴1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴Atomic model
Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.
Schematic atomic model, not to scale.
Atomic Fingerprint
Emission / Absorption Spectrum
Isotope Distribution
| Mass number | Atomic mass (u) | Natural abundance | Half-life |
|---|---|---|---|
| 76 Stable | 75.919213704 ± 0.000000017 | 9.3700% | Stable |
| 77 Stable | 76.919914154 ± 0.000000067 | 7.6300% | Stable |
| 78 Stable | 77.91730928 ± 0.0000002 | 23.7700% | Stable |
| 80 Stable | 79.9165218 ± 0.0000013 | 49.6100% | Stable |
Phase / State
Reason: 195.5 °C below melting point (220.5 °C)
Schematic, not to scale
Phase transition points
Transition energies
Energy required to melt 1 mol at melting point
Energy required to vaporize 1 mol at boiling point
Energy required to sublime 1 mol at sublimation point
Density
At standard conditions
At standard conditions
Advanced
Atomic Spectra
Showing 10 of 34. Sorted by ion charge (ascending).
Lines Holdings ?
| Ion | Charge | Total lines | Transition probabilities | Level designations |
|---|---|---|---|---|
| Se I | 0 | 138 | 0 | 0 |
| Se II | +1 | 39 | 0 | 0 |
| Se III | +2 | 39 | 0 | 0 |
| Se IV | +3 | 22 | 0 | 0 |
| Se V | +4 | 17 | 0 | 0 |
Levels Holdings ?
| Ion | Charge | Levels |
|---|---|---|
| Se I | 0 | 173 |
| Se II | +1 | 78 |
| Se III | +2 | 53 |
| Se IV | +3 | 29 |
| Se V | +4 | 15 |
| Se VI | +5 | 7 |
| Se VII | +6 | 45 |
| Se VIII | +7 | 37 |
| Se IX | +8 | 2 |
| Se X | +9 | 2 |
Ionic Radii
| Charge | Coordination | Spin | Radius |
|---|---|---|---|
| -2 | 6 | N/A | 198 pm |
| +4 | 6 | N/A | 50 pm |
| +6 | 4 | N/A | 28.000000000000004 pm |
| +6 | 6 | N/A | 42 pm |
Compounds
Isotopes (4)
Naturally selenium contains six stable isotopes. Fifteen other isotopes have been characterized. The element is a member of the sulfur family and resembles sulfur both in its various forms and in its compounds.
| Mass number | Atomic mass (u) | Natural abundance | Half-life | Decay mode | |
|---|---|---|---|---|---|
| 76 Stable | 75.919213704 ± 0.000000017 | 9.3700% ± 0.2900% | Stable | stable | |
| 77 Stable | 76.919914154 ± 0.000000067 | 7.6300% ± 0.1600% | Stable | stable | |
| 78 Stable | 77.91730928 ± 0.0000002 | 23.7700% ± 0.2800% | Stable | stable | |
| 80 Stable | 79.9165218 ± 0.0000013 | 49.6100% ± 0.4100% | Stable | stable |
Extended Properties
Covalent Radii (Extended)
- Covalent radius (Pyykkö)
- 116 pm
- Covalent radius (Pyykkö, double)
- 107 pm
- Covalent radius (Pyykkö, triple)
- 107 pm
- Covalent radius (Bragg)
- 117 pm
Van der Waals Radii
- Bondi
- 190 pm
- Batsanov
- 190 pm
- Alvarez
- 182 pm
- UFF
- 420.5 pm
- MM3
- 229 pm
- Dreiding
- 403 pm
Atomic & Metallic Radii
- Atomic radius (Rahm)
- 224 pm
- Metallic radius (C12)
- 140 pm
Numbering Scales
- Mendeleev
- 101
- Pettifor
- 93
- Glawe
- 95
Electronegativity Scales
- Ghosh
- 0
- Gunnarsson–Lundqvist
- 6
- Robles–Bartolotti
- 5
Polarizability & Dispersion
- Dipole polarizability
- 28.9 a.u.
- Dipole polarizability (unc.)
- 1 a.u.
- C₆
- 210 Ha·Bohr6
- C₆ (Gould–Bučko)
- 233 Ha·Bohr6
Supply Risk & Economics
- Production concentration
- 35
- Relative supply risk
- 7
- Reserve distribution
- 22
- Political stability (top producer)
- 77
- Political stability (top reserve)
- 18
Phase Transitions & Allotropes
| Transition temperature | 453.15 K |
| Boiling point | 958.15 K |
| Critical point (temperature) | 1766.15 K |
| Melting point | 493.95 K |
| Boiling point | 958.15 K |
| Critical point (temperature) | 1766.15 K |
| Critical point (pressure) | 27.2 MPa |
Oxidation State Categories
Advanced Reference Data
Screening Constants (8)
| n | Orbital | σ |
|---|---|---|
| 1 | s | 0.7378 |
| 2 | p | 3.9348 |
| 2 | s | 9.1116 |
| 3 | d | 15.523 |
| 3 | p | 15.295 |
| 3 | s | 14.5966 |
| 4 | p | 25.7128 |
| 4 | s | 24.2424 |
Crystal Radii Detail (4)
| Charge | CN | Spin | rcrystal (pm) | Origin |
|---|---|---|---|---|
| -2 | VI | 184 | Pauling's (1960) crystal radius, | |
| 4 | VI | 64 | Ahrens (1952) ionic radius, | |
| 6 | IV | 42 | ||
| 6 | VI | 56 | calculated, |
Isotope Decay Modes (52)
| Isotope | Mode | Intensity |
|---|---|---|
| 63 | B+ | 100% |
| 63 | B+p | 89% |
| 63 | 2p | 0.5% |
| 64 | B+ | — |
| 64 | B+p | — |
| 65 | B+ | 100% |
| 65 | B+p | 87% |
| 66 | B+ | 100% |
| 66 | B+p | — |
| 67 | B+ | 100% |
X‑ray Scattering Factors (506)
| Energy (eV) | f₁ | f₂ |
|---|---|---|
| 10 | — | 5.20241 |
| 10.1617 | — | 5.36005 |
| 10.3261 | — | 5.52247 |
| 10.4931 | — | 5.63017 |
| 10.6628 | — | 5.66221 |
| 10.8353 | — | 5.69443 |
| 11.0106 | — | 5.71762 |
| 11.1886 | — | 5.72709 |
| 11.3696 | — | 5.73659 |
| 11.5535 | — | 5.7461 |
Additional Data
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
5×10-2 milligrams per kilogram
References (1)
- [5] Selenium https://education.jlab.org/itselemental/ele034.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
2×10-4 milligrams per liter
References (1)
- [5] Selenium https://education.jlab.org/itselemental/ele034.html
Production
Production of this element (from raw materials or other compounds containing the element).
Selenium is found in a few rare minerals such as crooksite and clausthalite. In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode metal from electrolytic copper refineries now provide the source of most of the world's selenium. Selenium is recovered by roasting the mud with soda or sulfuric acid, or by smelting them with soda and niter.
References (1)
- [6] Selenium https://periodic.lanl.gov/34.shtml
References
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
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The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Selenium.
The element property data was retrieved from publications.