Selenium (Se)
nonmetalSolid
Peso atomico standard
78,971 uConfigurazione elettronica
[Ar] 4s2 3d10 4p4Punto di fusione
220,5 °CPunto di ebollizione
684,85 °CDensità
4809 kg/m³Stati di ossidazione
−2, −1, 0, +1, +2, +3, +4, +5, +6Elettronegatività (Pauling)
2,55Energia di ionizzazione (1ª)
9,752368 eVAnno della scoperta
1817Raggio atomico
115 pmDettagli
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.
Immagini
Proprietà
Fisiche
- Raggio atomico (empirico)
- 115 pm Confronta Raggio atomico (empirico) di tutti gli elementi →
- Raggio covalente
- 120 pm Confronta Raggio covalente di tutti gli elementi →
- Raggio di van der Waals
- 190 pm Confronta Raggio di van der Waals di tutti gli elementi →
- Raggio metallico
- 117 pm Confronta Raggio metallico di tutti gli elementi →
- Densità
- 4809 kg/m³ Confronta Densità di tutti gli elementi →
- Volume molare
- 0,0165 L/mol
- Fase in condizioni STP
- Solido Confronta Fase in condizioni STP di tutti gli elementi →
- Punto di fusione
- 220,5 °C Confronta Punto di fusione di tutti gli elementi →
- Punto di ebollizione
- 684,85 °C Confronta Punto di ebollizione di tutti gli elementi →
- Conducibilità termica
- 0,52 W/(m·K) Confronta Conducibilità termica di tutti gli elementi →
- Capacità termica specifica
- 0,321 J/(g·K) Confronta Capacità termica specifica di tutti gli elementi →
- Capacità termica molare
- 25,363 J/(mol·K) Confronta Capacità termica molare di tutti gli elementi →
- Struttura cristallina
- Esagonale compatta Confronta Struttura cristallina di tutti gli elementi →
Chimiche
- Elettronegatività (Pauling)
- 2,55 Confronta Elettronegatività (Pauling) di tutti gli elementi →
- Elettronegatività (Allen)
- 2,424
- Affinità elettronica
- 2,0206 eV
- Energia di ionizzazione (1ª)
- 9,752368 eV Confronta Energia di ionizzazione (1ª) di tutti gli elementi →
- Energia di ionizzazione (2ª)
- 21,196073 eV Confronta Energia di ionizzazione (2ª) di tutti gli elementi →
- Energia di ionizzazione (3ª)
- 31,697109 eV Confronta Energia di ionizzazione (3ª) di tutti gli elementi →
- Energia di ionizzazione (4ª)
- 42,947148 eV Confronta Energia di ionizzazione (4ª) di tutti gli elementi →
- Energia di ionizzazione (5ª)
- 68,300235 eV Confronta Energia di ionizzazione (5ª) di tutti gli elementi →
- Stati di ossidazione
- −2, −1, 0, +1, +2, +3, +4, +5, +6 Confronta Stati di ossidazione di tutti gli elementi →
- Elettroni di valenza
- 6 Confronta Elettroni di valenza di tutti gli elementi →
- Allotropi
- ["gray", "vitreous"]
- Configurazione elettronica
- [Ar] 4s2 3d10 4p4
Termodinamiche
- Punto critico (temperatura)
- 1493 °C
- Calore di fusione
- 0,0693372 eV Confronta Calore di fusione di tutti gli elementi →
- Calore di vaporizzazione
- 0,27258123 eV Confronta Calore di vaporizzazione di tutti gli elementi →
- Calore di sublimazione
- 2,352697 eV
- Calore di atomizzazione
- 2,352697 eV
- Entalpia di atomizzazione
- 2,35477 eV
Nucleari
- Protoni
- 34 Confronta Protoni di tutti gli elementi →
- Neutroni
- 46 Confronta Neutroni di tutti gli elementi →
- Isotopi noti
- 33 Confronta Isotopi noti di tutti gli elementi →
- Isotopi stabili
- 4 Confronta Isotopi stabili di tutti gli elementi →
- Isotopo più stabile
- Se-80
- Anno della scoperta
- 1817
Abbondanza
- Abbondanza (crosta terrestre)
- 0,05 mg/kg Confronta Abbondanza (crosta terrestre) di tutti gli elementi →
- Abbondanza (oceano)
- 2 × 10−4 mg/L Confronta Abbondanza (oceano) di tutti gli elementi →
Struttura cristallina
- Costante reticolare a
- 436 pm
Struttura elettronica
- Elettroni per guscio
- 2, 8, 18, 6 Confronta Elettroni per guscio di tutti gli elementi →
Identificativi
- Numero CAS
- 7782-49-2 Confronta Numero CAS di tutti gli elementi →
- Simbolo di termine
- 3P2
- InChI
- InChI=1S/Se
- Chiave InChI
- BUGBHKTXTAQXES-UHFFFAOYSA-N
Configurazione elettronica Misurato
Se: 3d¹⁰ 4s² 4p⁴[Ar] 3d¹⁰ 4s² 4p⁴1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴Modello atomico
Gli isotopi modificano il numero di neutroni, la massa e la stabilità — non la configurazione elettronica di un atomo neutro.
Modello atomico schematico, non in scala.
Impronta atomica
Spettro di emissione / assorbimento
Distribuzione isotopica
| Numero di massa | Massa atomica (u) | Abbondanza naturale | Emivita |
|---|---|---|---|
| 76 Stabile | 75,919213704 ± 0,000000017 | 9,3700% | Stabile |
| 77 Stabile | 76,919914154 ± 0,000000067 | 7,6300% | Stabile |
| 78 Stabile | 77,91730928 ± 0,0000002 | 23,7700% | Stabile |
| 80 Stabile | 79,9165218 ± 0,0000013 | 49,6100% | Stabile |
Fase / Stato
Motivo: 195,5 °C sotto il punto di fusione (220,5 °C)
Schema non in scala
Punti di transizione di fase
Energie di transizione
Energia necessaria per fondere 1 mol al punto di fusione
Energia necessaria per vaporizzare 1 mol al punto di ebollizione
Energia necessaria per sublimare 1 mol al punto di sublimazione
Densità
In condizioni standard
In condizioni standard
Avanzate
Spettri atomici
Sono visualizzati 10 di 34. Ordinamento per carica ionica crescente.
Righe disponibili ?
| Ione | Carica | Righe totali | Probabilità di transizione | Designazioni dei livelli |
|---|---|---|---|---|
| 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 |
Livelli disponibili ?
| Ione | Carica | Livelli |
|---|---|---|
| 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 |
Raggi ionici
| Carica | Coordinazione | Spin | Raggio |
|---|---|---|---|
| -2 | 6 | N/D | 198 pm |
| +4 | 6 | N/D | 50 pm |
| +6 | 4 | N/D | 28.000000000000004 pm |
| +6 | 6 | N/D | 42 pm |
Composti
Isotopi (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.
| Numero di massa | Massa atomica (u) | Abbondanza naturale | Emivita | Modalità di decadimento | |
|---|---|---|---|---|---|
| 76 Stabile | 75,919213704 ± 0,000000017 | 9,3700% ± 0,2900% | Stabile | stable | |
| 77 Stabile | 76,919914154 ± 0,000000067 | 7,6300% ± 0,1600% | Stabile | stable | |
| 78 Stabile | 77,91730928 ± 0,0000002 | 23,7700% ± 0,2800% | Stabile | stable | |
| 80 Stabile | 79,9165218 ± 0,0000013 | 49,6100% ± 0,4100% | Stabile | stable |
Proprietà estese
Raggi covalenti (dati estesi)
- Raggio covalente (Pyykkö)
- 116 pm
- Raggio covalente (Pyykkö, legame doppio)
- 107 pm
- Raggio covalente (Pyykkö, legame triplo)
- 107 pm
- Raggio covalente (Bragg)
- 117 pm
Raggi di van der Waals
- Bondi
- 190 pm
- Batsanov
- 190 pm
- Alvarez
- 182 pm
- UFF
- 420,5 pm
- MM3
- 229 pm
- Dreiding
- 403 pm
Raggi atomici e metallici
- Raggio atomico (Rahm)
- 224 pm
- Raggio metallico (C12)
- 140 pm
Scale di numerazione
- Mendeleev
- 101
- Pettifor
- 93
- Glawe
- 95
Scale di elettronegatività
- Ghosh
- 0
- Gunnarsson–Lundqvist
- 6
- Robles–Bartolotti
- 5
Polarizzabilità e dispersione
- Polarizzabilità dipolare
- 28,9 a.u.
- Polarizzabilità dipolare (inc.)
- 1 a.u.
- C₆
- 210 Ha·Bohr6
- C₆ (Gould–Bučko)
- 233 Ha·Bohr6
Rischio di approvvigionamento ed economia
- Concentrazione della produzione
- 35
- Rischio relativo di approvvigionamento
- 7
- Distribuzione delle riserve
- 22
- Stabilità politica (principale produttore)
- 77
- Stabilità politica (principale detentore di riserve)
- 18
Transizioni di fase e allotropi
| Temperatura di transizione | 453,15 K |
| Punto di ebollizione | 958,15 K |
| Punto critico (temperatura) | 1766,15 K |
| Punto di fusione | 493,95 K |
| Punto di ebollizione | 958,15 K |
| Punto critico (temperatura) | 1766,15 K |
| Punto critico (pressione) | 27,2 MPa |
Categorie degli stati di ossidazione
Dati di riferimento avanzati
Costanti di schermaggio (8)
| n | Orbitale | 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 |
Dettaglio dei raggi cristallini (4)
| Carica | CN | Spin | rcrystal (pm) | Origine |
|---|---|---|---|---|
| -2 | VI | 184 | Pauling's (1960) crystal radius, | |
| 4 | VI | 64 | Ahrens (1952) ionic radius, | |
| 6 | IV | 42 | ||
| 6 | VI | 56 | calculated, |
Modalità di decadimento degli isotopi (52)
| Isotopo | Modalità | Intensità |
|---|---|---|
| 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% |
Fattori di diffusione dei raggi X (506)
| Energia (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 |
Dati aggiuntivi
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
5×10-2 milligrams per kilogram
Riferimenti (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
Riferimenti (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.
Riferimenti (1)
- [6] Selenium https://periodic.lanl.gov/34.shtml
Riferimenti
(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.
Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/
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.