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About Selenium

Selenium Bohr

In 1817 the chemists Jons Jakob Berzelius and Johan Gottlieb Gahn decided to investigate a strange red precipitate found by workers at a sulfuric acid plant that they owned together. Initially, the material was believed to be a form of arsenic, which had led workers to discontinue use of the pyrite that had produced it, but the chemists noted that it did not have the expected properties for an arsenic compound. Tellurium was a closer fit, as the powder gave off a smell when burned that was known to be associated with that element, but further investigation showed that the element could not be tellurium either, and the chemists eventually recognized that they had discovered a previously unknown element. Tellurium’s name means “earth,” and Berzelius decided to name the new element for Selene, the moon, because of the similarities between the two.

Selenium is a semiconductor that can take a variety of crystalline structures depending on the conditions under which it is formed. The brick red powder found by Berzelius and Gahn was the form encountered most often as a result of chemical reactions, and when rapidly melted it produces a black vitreous solid often sold industrially, but the most stable form is a dense grey solid. In 1873, Willoughby Smith showed that the electric resistance of grey selenium varies predictably depending on incident light. This property is known as photoconductivity, and tellurium is now known to exhibit it as well, though to a lesser degree. The earliest major uses of selenium were in semiconductor devices such as rectifiers in radio and television tubes, which served to replace the previously used vacuum tubes and which preceded the silicon-based components used today.

Despite the rise of silicon as the major industrial semiconductor, selenium remains relevant to semiconductor technologies. While most selenium rectifiers have been replaced by other technologies, selenium remains in use for surge protection devices in some high-energy DC circuits. As a component of the compound semiconductors copper indium gallium selenide (CIGS), indium selenide, gallium selenide, cadmium selenide, and zinc selenide, selenium is essential for production of many thin-film solar cells, and is additionally found in electro-optical devices such as LEDs, lasers, and photoresistors. Notably, recently researchers have shown great interest in the possibilities of using cadmium selenide nanocrystals known as quantum dots in novel solar cells, more efficient LEDs, and in biomedical imaging applications.

Pure amorphous selenium was once a component of every photocopier, where its role as a photoconductor allowed for the production of images based on the areas of light shining through a printed document. Today organic photoconductors have largely replaced selenium in this role, but selenium can also produce images based on exposure to x-rays--images that may be transferred to paper, as in a photocopier, or read directly from charge patterns on the selenium into a computer via a thin film transistor array. This type of x-ray technology never rose to popularity during the age of x-ray films, but has seen renewed interest as digital x-ray imaging systems become the norm. Therefore, amorphous selenium is now is found in many flat-panel digital x-ray machines for medical and dental imaging.

Selenium serves several key functions outside its role as a photoconductive semiconductor. As a component of cadmium sulfoselenide pigments, it can impart a brilliant ruby red hue to materials which incorporate it. In glassmaking, selenium salts are added in small amounts because the red tone cancels out the green tinge lent by iron impurities. Selenium is a component of metal alloys, where it improves machinability of the final material and often replaces the more toxic metal lead.

Though excessive quantities of selenium can be toxic, the element is also an important micronutrient, as it is a necessary cofactor for several enzymes. Because of this key biological role, selenium is sometimes included in nutritional supplements. Notably, the major mechanism of mercury poisoning is the permanent inactivation of these essential enzymes caused by a reaction between mercury and selenium. Therefore the effects of some types of mercury exposure can be partially mitigated by sufficient selenium intake.

Selenium is produced primarily as a byproduct of copper refining, but is also recycled from scrap.


Semiconductor & Optical
Sputtering Targets
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High Purity (99.999%) Selenium (Se) Sputtering Target Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. Below its melting point, selenium is a p-type semiconductor and has many uses in electronics applications. Selenium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity). Elemental or metallic forms include pellets, rod, wire and granules for evaporation source material purposes. Selenium oxide is available in powder and dense pellet form for such uses as optical coating and thin film applications. Oxides tend to be insoluble. Selenium fluoride is another insoluble form for uses in which oxygen is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Selenium is also available in soluble forms including chlorides. These compounds can be manufactured as solutions at specified stoichiometries.

Selenium Properties

Selenide(Se) atomic and molecular weight, atomic number and elemental symbolSelenium is a Block P, Group 16, Period 4 element. The number of electrons in each of Selenium's shells is 2, 8, 18, 6 and its electron configuration is [Ar] 3d10 4s2 4p4. Selenium Bohr ModelSelenium was discovered and first isolated by Jöns Jakob Berzelius and Johann Gottlieb Gahn in 1817. It is produced from selenide which is found in many sulfide ores. The origin of the name Selenium comes from the Greek word "Selênê" meaning moon.

Symbol: Se
Atomic Number: 34
Atomic Weight: 78.96
Element Category: nonmetal
Group, Period, Block: 16 (chalcogens), 4, p
Color: gray or red (crystalline), black or red (amorphous)
Other Names: Selen, Selenio
Melting Point: 220.8°C, 429.44°F, 493.95 K
Boiling Point: 685°C, 1265°F, 958.15 K
Density: 4808 kg·m3
Liquid Density @ Melting Point: 3.99 g·cm3
Density @ 20°C: 4.79 g/cm3
Density of Solid: 4819 kg·m3
Specific Heat: 0.767 Cal/g/K @ 25 °C
Superconductivity Temperature: N/A
Triple Point: N/A
Critical Point: 1766 K, 27.2 MPa
Heat of Fusion (kJ·mol-1): 5.1
Heat of Vaporization (kJ·mol-1): 90
Heat of Atomization (kJ·mol-1): 226.4
Thermal Conductivity: 0.00519 W/cm/K @ 298.2 K
Thermal Expansion: (25 °C) (amorphous) 37 µm·m-1·K-1
Electrical Resistivity: 106 nΩ-cm @ 0°C
Tensile Strength: N/A
Molar Heat Capacity: 25.363 J·mol-1·K-1
Young's Modulus: 10 GPa
Shear Modulus: 3.7 GPa
Bulk Modulus: 8.3 GPa
Poisson Ratio: 0.33
Mohs Hardness: 2
Vickers Hardness: N/A
Brinell Hardness: 736 MPa
Speed of Sound: (20 °C) 3350 m·s-1
Pauling Electronegativity: 2.55
Sanderson Electronegativity: 3.01
Allred Rochow Electronegativity: 2.48
Mulliken-Jaffe Electronegativity: 2.60 (16.7% s orbital)
Allen Electronegativity: 2.424
Pauling Electropositivity: 1.45
Reflectivity (%): N/A
Refractive Index: 1.000895
Electrons: 34
Protons: 34
Neutrons: 45
Electron Configuration: [Ar] 3d10 4s2 4p4
Atomic Radius: 120 pm
Atomic Radius,
non-bonded (Å):
Covalent Radius: 120±4 pm
Covalent Radius (Å): 1.18
Van der Waals Radius: 190 pm
Oxidation States: 6, 4, -2
Phase: Solid
Crystal Structure: hexagonal
Magnetic Ordering: diamagnetic
Electron Affinity (kJ·mol-1) 194.997
1st Ionization Energy: 940.97 kJ·mol-1
2nd Ionization Energy: 2044.54 kJ·mol-1
3rd Ionization Energy: 2973.74 kJ·mol-1
CAS Number: 7782-49-2
EC Number: 231-957-4
MDL Number: MFCD00134090
Beilstein Number: N/A
SMILES Identifier: [Se]
InChI Identifier: InChI=1S/Se
PubChem CID: 6326970
ChemSpider ID: 4885617
Earth - Total: 9.6 ppm
Mercury - Total:  0.79 ppm
Venus - Total: 5.4 ppm
Earth - Seawater (Oceans), ppb by weight: 0.45
Earth - Seawater (Oceans), ppb by atoms: 0.035
Earth -  Crust (Crustal Rocks), ppb by weight: 50
Earth -  Crust (Crustal Rocks), ppb by atoms: 10
Sun - Total, ppb by weight: N/A
Sun - Total, ppb by atoms: N/A
Stream, ppb by weight: 0.2
Stream, ppb by atoms: 0.003
Meterorite (Carbonaceous), ppb by weight: 13000
Meterorite (Carbonaceous), ppb by atoms: 2900
Typical Human Body, ppb by weight: N/A
Typical Human Body, ppb by atom: N/A
Universe, ppb by weight: 0.1
Universe, ppb by atom: 0.001
Discovered By: Jöns Jakob Berzelius and Johann Gottlieb Gahn
Discovery Date: 1817
First Isolation: Jöns Jakob Berzelius and Johann Gottlieb Gahn (1817)

Health, Safety & Transportation Information for Selenium

The EPA does not classify selenium as carcinogenic, although selenium sulfide is a probable carcinogen. Selenates and selenites which are compounds of selenium, are highly toxic. Hydrogen selenide gas (SeH2) is the most acutely toxic compound of selenium. Safety data for Selenium and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the Products tab. The below information applies to elemental Selenium.

Safety Data
Signal Word Danger
Hazard Statements H301-H331-H373-H413
Hazard Codes T
Risk Codes 23/25-33-53
Safety Precautions 20/21-28-45-61
RTECS Number VS7700000
Transport Information N/A
WGK Germany 3
Globally Harmonized System of
Classification and Labelling (GHS)
Skull and Crossbones-Acute Toxicity  Health Hazard
Review and Print SDS for Elemental Selenium


Date Created: 05/15/2015
Date Revised: 05/15/2015


Product Name: Selenium Metal

Product Number: All applicable American Elements product codes, e.g. SE-E-02, SE-E-03, SE-E-04, SE-E-05, SE-E-06, SE-E-07

CAS #: 7782-49-2

Relevant identified uses of the substance: Scientific research and development

Supplier details:
American Elements
1093 Broxton Ave. Suite 2000
Los Angeles, CA 90024
Tel: +1 310-208-0551
Fax: +1 310-208-0351

Emergency telephone number:
Domestic, North America +1 800-424-9300
International +1 703-527-3887


Classification of the substance or mixture
Classification according to Regulation (EC) No 1272/2008
GHS06 Skull and crossbones
Acute Tox. 3 H301 Toxic if swallowed.
Acute Tox. 3 H331 Toxic if inhaled.
GHS08 Health hazard
STOT RE 2 H373 May cause damage to the liver and the reproductive system through prolonged or repeated exposure. Route of exposure: Oral.
Hazards not otherwise classified
No information known.
Label elements
Labelling according to Regulation (EC) No 1272/2008
The substance is classified and labeled according to the CLP regulation.
Hazard pictograms

Skull and Crossbones - GHS06 Health Hazard - GHS08

Signal word
Hazard statements
H301+H331 Toxic if swallowed or if inhaled.
H373 May cause damage to the liver and the reproductive system through prolonged or repeated exposure. Route of exposure: Oral.
Precautionary statements
P260 Do not breathe dust/fume/gas/mist/vapours/spray.
P261 Avoid breathing dust/fume/gas/mist/vapours/spray.
P304+P340 IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing.
P405 Store locked up.
P403+P233 Store in a well-ventilated place. Keep container tightly closed.
P501 Dispose of contents/container in accordance with local/regional/
national/international regulations.
WHMIS classification
D1A - Very toxic material causing immediate and serious toxic effects
Classification system
HMIS ratings (scale 0-4)
(Hazardous Materials Identification System)

Health (acute effects) = 1
Flammability = 0
Physical Hazard = 0
Other hazards
Results of PBT and vPvB assessment
Not applicable.
Not applicable.


Chemical characterization: Substances
CAS# Description:
7782-49-2 Selenium
Identification number(s):
EC number:
Index number:


Description of first aid measures
General information
Immediately remove any clothing soiled by the product.
Remove breathing apparatus only after contaminated clothing has been completely removed.
In case of irregular breathing or respiratory arrest provide artificial respiration.
No special measures required.
After inhalation
Seek medical treatment in case of complaints.
After skin contact
Generally the product does not irritate the skin.
After eye contact
Rinse opened eye for several minutes under running water. If symptoms persist, consult a doctor.
After swallowing
Do not induce vomiting; immediately call for medical help.
Information for doctor
Most important symptoms and effects, both acute and delayed
No further relevant information available.
Indication of any immediate medical attention and special treatment needed
No further relevant information available.


Extinguishing media
Suitable extinguishing agents
Product is not flammable. Use fire-fighting measures that suit the surrounding fire.
Special hazards arising from the substance or mixture
If this product is involved in a fire, the following can be released:
Selenium dioxide (SeO2)
Advice for firefighters
Protective equipment:
No special measures required.


Personal precautions, protective equipment and emergency procedures
Not required.
Environmental precautions:
Do not allow material to be released to the environment without proper governmental permits.
Methods and material for containment and cleaning up:
Dispose of contaminated material as waste according to section 13.
Ensure adequate ventilation.
Prevention of secondary hazards:
No special measures required.
Reference to other sections
See Section 7 for information on safe handling
See Section 8 for information on personal protection equipment.
See Section 13 for disposal information.


Precautions for safe handling
Keep container tightly sealed.
Store in cool, dry place in tightly closed containers.
Ensure good ventilation at the workplace.
Open and handle container with care.
Information about protection against explosions and fires:
The product is not flammable
No special measures required.
Conditions for safe storage, including any incompatibilities
Requirements to be met by storerooms and receptacles:
No special requirements.
Information about storage in one common storage facility:
Not required.
Further information about storage conditions:
Keep container tightly sealed.
Store in cool, dry conditions in well sealed containers.
Specific end use(s)
No further relevant information available.


Additional information about design of technical systems:
No further data; see section 7.
Control parameters
Components with limit values that require monitoring at the workplace:
7782-49-2 Selenium (100.0%)
PEL (USA) Long-term value: 0.2 mg/m³
as Se
REL (USA) Long-term value: 0.2 mg/m³
as Se
TLV (USA) Long-term value: 0.2 mg/m³
as Se
EL (Canada) Long-term value: 0.1 mg/m³
EV (Canada) Long-term value: 0.2 mg/m³
Additional information:
No data
Exposure controls
Personal protective equipment
General protective and hygienic measures
The usual precautionary measures for handling chemicals should be followed.
Store protective clothing separately.
Maintain an ergonomically appropriate working environment.
Breathing equipment:
Not required.
Use self-contained respiratory protective device in emergency situations.
Protection of hands:
Not required.
Penetration time of glove material (in minutes)
Not determined
Eye protection:
Safety glasses
Body protection:
Protective work clothing.


Information on basic physical and chemical properties
General Information
Form: Solid in various forms
Color: Various colors
Odor: Odorless
Odor threshold: Not determined.
pH-value: Not applicable.
Change in condition
Melting point/Melting range: 217 °C (423 °F)
Boiling point/Boiling range: 685 °C (1265 °F)
Sublimation temperature / start: Not determined
Flammability (solid, gaseous)
Not determined.
Ignition temperature: Not determined
Decomposition temperature: Not determined
Auto igniting: Not determined.
Danger of explosion: Not determined.
Explosion limits:
Lower: Not determined
Upper: Not determined
Vapor pressure: Not applicable.
Density at 20 °C (68 °F): 4.28 g/cm³ (35.717 lbs/gal)
Relative density
Not determined.
Vapor density
Not applicable.
Evaporation rate
Not applicable.
Solubility in / Miscibility with Water: Insoluble
Partition coefficient (n-octanol/water): Not determined.
dynamic: Not applicable.
kinematic: Not applicable.
Other information
No further relevant information available.


No information known.
Chemical stability
Stable under recommended storage conditions.
Thermal decomposition / conditions to be avoided:
Decomposition will not occur if used and stored according to specifications.
Possibility of hazardous reactions
No dangerous reactions known
Conditions to avoid
No further relevant information available.
Incompatible materials:
No information known.
Hazardous decomposition products:
Selenium dioxide (SeO2)


Information on toxicological effects
Acute toxicity:
Toxic if inhaled.
Toxic if swallowed.
The Registry of Toxic Effects of Chemical Substances (RTECS) contains acute toxicity data for this substance.
LD/LC50 values that are relevant for classification:
No data
Skin irritation or corrosion:
No irritant effect.
Eye irritation or corrosion:
No irritant effect.
No sensitizing effects known.
Germ cell mutagenicity:
No effects known.
EPA-D: Not classifiable as to human carcinogenicity: inadequate human and animal evidence of carcinogenicity or no data are available.
IARC-3: Not classifiable as to carcinogenicity to humans.
The Registry of Toxic Effects of Chemical Substances (RTECS) contains tumorigenic and/or carcinogenic and/or neoplastic data for this substance.
Reproductive toxicity:
The Registry of Toxic Effects of Chemical Substances (RTECS) contains reproductive data for this substance.
Specific target organ system toxicity - repeated exposure:
May cause damage to the liver and the reproductive system through prolonged or repeated exposure. Route of exposure: Oral.
Specific target organ system toxicity - single exposure:
No effects known.
Aspiration hazard:
No effects known.
Subacute to chronic toxicity:
The Registry of Toxic Effects of Chemical Substances (RTECS) contains multiple dose toxicity data for this substance.
Additional toxicological information:
To the best of our knowledge the acute and chronic toxicity of this substance is not fully known.
Carcinogenic categories
OSHA-Ca (Occupational Safety & Health Administration)
Substance is not listed.


Aquatic toxicity:
No further relevant information available.
Persistence and degradability
No further relevant information available.
Bioaccumulative potential
No further relevant information available.
Mobility in soil
No further relevant information available.
Additional ecological information:
General notes:
Do not allow product to reach ground water, water course or sewage system.
Do not allow material to be released to the environment without proper governmental permits.
Danger to drinking water if even small quantities leak into the ground.
May cause long lasting harmful effects to aquatic life.
Avoid transfer into the environment.
Results of PBT and vPvB assessment
Not applicable.
Not applicable.
Other adverse effects
No further relevant information available.


Waste treatment methods
Consult state, local or national regulations to ensure proper disposal.
Uncleaned packagings:
Disposal must be made according to official regulations.


Not applicable
UN proper shipping name
Not applicable
Transport hazard class(es)
Not applicable
Packing group
Not applicable
Environmental hazards:
Not applicable.
Special precautions for user
Not applicable.
Transport in bulk according to Annex II of MARPOL73/78 and the IBC Code
Not applicable.
Transport/Additional information:
Marine Pollutant (DOT):


Safety, health and environmental regulations/legislation specific for the substance or mixture
National regulations
All components of this product are listed in the U.S. Environmental Protection Agency Toxic Substances Control Act Chemical substance Inventory.
All components of this product are listed on the Canadian Domestic Substances List (DSL).
SARA Section 313 (specific toxic chemical listings)
7782-49-2 Selenium
California Proposition 65
Prop 65 - Chemicals known to cause cancer
Substance is not listed.
Prop 65 - Developmental toxicity
Substance is not listed.
Prop 65 - Developmental toxicity, female
Substance is not listed.
Prop 65 - Developmental toxicity, male
Substance is not listed.
Information about limitation of use:
For use only by technically qualified individuals.
This product is subject to the reporting requirements of section 313 of the Emergency Planning and Community Right to Know Act of 1986 and 40CFR372.
Other regulations, limitations and prohibitive regulations
Substance of Very High Concern (SVHC) according to the REACH Regulations (EC) No. 1907/2006.
Substance is not listed.
The conditions of restrictions according to Article 67 and Annex XVII of the Regulation (EC) No 1907/2006 (REACH) for the manufacturing, placing on the market and use must be observed.
Substance is not listed.
Annex XIV of the REACH Regulations (requiring Authorisation for use)
Substance is not listed.
Chemical safety assessment:
A Chemical Safety Assessment has not been carried out.


Safety Data Sheet according to Regulation (EC) No. 1907/2006 (REACH). The above information is believed to be correct but does not purport to be all inclusive and shall be used only as a guide. The information in this document is based on the present state of our knowledge and is applicable to the product with regard to appropriate safety precautions. It does not represent any guarantee of the properties of the product. American Elements shall not be held liable for any damage resulting from handling or from contact with the above product. See reverse side of invoice or packing slip for additional terms and conditions of sale. COPYRIGHT 1997-2016 AMERICAN ELEMENTS. LICENSED GRANTED TO MAKE UNLIMITED PAPER COPIES FOR INTERNAL USE ONLY.

Selenium Isotopes

Selenium (Se) has six naturally occurring isotopes. Five of these are stable: 74Se, 76Se, 77Se, 78Se, and 80Se.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
65Se 64.96466(64)# <50 ms ß+ to 65As; ß+ + p to 64Ge 3/2-# N/A 520.5 -
66Se 65.95521(32)# 33(12) ms ß+ to 66As 0+ N/A 536.97 -
67Se 66.95009(21)# 133(11) ms ß+ to 67As; ß+ + p to 66Ge 5/2-# N/A 549.7 -
68Se 67.94180(4) 35.5(7) s ß+ to 68Br 0+ N/A 566.17 -
69Se 68.93956(4) 27.4(2) s ß+ to 69As; ß+ + p to 68Ge (1/2-) N/A 576.11 -
70Se 69.93339(7) 41.1(3) min EC to 70As 0+ N/A 589.78 -
71Se 70.93224(3) 4.74(5) min EC to 71As 5/2- N/A 598.79 -
72Se 71.927112(13) 8.40(8) d EC to 72As 0+ N/A 611.53 -
73Se 72.926765(11) 7.15(8) h EC to 73As 9/2+ N/A 620.54 -
74Se 73.9224764(18) Observationally Stable - 0+ N/A 632.34 0.89
75Se 74.9225234(18) 119.779(4) d EC to 75As 5/2+ 0.67 640.42 -
76Se 75.9192136(18) STABLE - 0+ N/A 651.29 9.37
77Se 76.9199140(18) STABLE - 1/2- 0.53506 659.37 7.63
78Se 77.9173091(18) STABLE - 0+ N/A 669.31 23.77
79Se 78.9184991(18) 2.95(38)E+5 y ß- to 79Br 7/2+ -1.018 676.46 -
80Se 79.9165213(21) Observationally Stable - 0+ N/A 686.4 49.61
81Se 80.9179925(22) 18.45(12) min ß- to 81Br 1/2- N/A 693.55 -
82Se 81.9166994(22) 97(5)E+18 y - to 82Kr 0+ N/A 702.56 8.73
83Se 82.919118(4) 22.3(3) min ß- to 83Br 9/2+ N/A 707.84 -
84Se 83.918462(16) 3.1(1) min ß- to 84Br 0+ N/A 716.85 -
85Se 84.92225(3) 31.7(9) s ß- to 85Br (5/2+)# N/A 721.21 -
86Se 85.924272(17) 15.3(9) s ß- to 86Br 0+ N/A 727.42 -
87Se 86.92852(4) 5.50(12) s ß- to 87Br; ß- + n to 86Br (5/2+)# N/A 731.77 -
88Se 87.93142(5) 1.53(6) s ß- to 88Br; ß- + n to 87Br 0+ N/A 737.06 -
89Se 88.93645(32)# 0.41(4) s ß- to 89Br; ß- + n to 88Br (5/2+)# N/A 740.48 -
90Se 89.93996(43)# 300# ms [>300 ns] ß- + n to 91Br; ß- to 92Br 0+ N/A 745.76 -
91Se 90.94596(54)# 270(50) ms ß- to 91Br; ß- + n to 90Br 1/2+# N/A 748.25 -
92Se 91.94992(64)# 100# ms [>300 ns] ß- to 92Br 0+ N/A 752.6 -
93Se 92.95629(86)# 50# ms [>300 ns] Unknown 1/2+# N/A 754.16 -
94Se 93.96049(86)# 20# ms [>300 ns] Unknown 0+ N/A 758.51 -