Element Selenium

Selenium ElementIt is a chemical element with the symbol Se and atomic number 34.
It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic.
Element Selenium rarely occurs in its elemental state or as pure ore compounds in the Earth’s crust. Selenium (from Ancient Greek σελήνη (selḗnē) “Moon”) was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium (named for the Earth).
Selenium is found in metal sulfide ores, where it partially replaces the sulfur.
Commercially, selenium is produced as a byproduct in the refining of these ores, most often during production. Minerals that are pure selenide or selenate compounds are known but rare.

Names and Identifiers

Chemical Formula:Se
CAS:7782-49-2
Molecular Weight:78.960g/mol
EC Number :231-957-4
MDL Number:MFCD00134090
Color:gray or red (crystalline), black or red (amorphous)
Other Names:Selen, Selenio
PubChem CID:6326970
IUPAC Name:Selenium
Inchl:InChI=1S/Se
InChI Key:BUGBHKTXTAQXES-UHFFFAOYSA-N
Canonical SMILES:[Se]
ICSC Number:0072

Physical & Chemical Properties

Phase:Solid
Density:4.81 g/cm³
Boiling Point:958 K ​(685 °C, ​1265 °F)
Melting Point:494 K ​(221 °C, ​430 °F)
Molecular Formula:Se
Flash Point:n/a
Exact Mass:79.916519
Symbol:Globally Harmonized System of ClassificationGlobally Harmonized System of Classification
Signal Word:Danger
Hazard Statements:H301 + H331-H373-H413
Precautionary Statements:P261-P301 + P310-P311
Hazard Codes:T:Toxic
Risk Phrases:R23/25;R33;R53
Safety Phrases:S26-S61-S45-S28-S20/21-S28A
RIDADR:UN 3440 6.1/PG 3
WGK Germany:2
RTECS:VS7700000
Packaging Group:III
Hazard Class:n/a

Selenium isotopes are mainly used for the production of medical and industrial radioisotopes.

Se-77 and Se-78 are used for the production of the therapeutic radioisotope Br-77. Se-80 is used for the production of the medical radioisotope Br-80m. Se-74 is used for the production of Se-75 which is used as a source in gamma radiography. Se-76 can be used for the production of the medical isotopes Br-75 and Br-76. Se-82 has been used to study double beta decay. Most of the Selenium isotopes have been used in studies into the role of Selenium as an essential nutrient.

Naturally occurring isotopes

IsotopeMass/DaNatural abundance (atom %)Nuclear spin (I)Magnetic moment (μ/μN)
74Se73.9224746 (16)0.89 (4)0
76Se75.9192120 (16)9.37 (29)0
77Se76.9199125 (16)7.63 (16)1/20.53506
78Se77.9173076 (16)23.77 (28)0
80Se79.9165196 (19)49.61 (41)0
82Se81.9166978 (23)8.73 (22)0

Radiosotope data

IsotopeMass/DaHalf-lifeMode of decayNuclear spinNuclear magnetic moment
70Se69.933541.1 mEC to 70As0
71Se70.93194.7 mEC to 71As5/2
72Se71.927118.5 dEC to 72As0
73Se72.926787.1 hEC to 73As9/2
75Se74.922524119.78 dEC to 75As5/20.67
79Se78.91850065000 yβ to 79Br0-1.018
81Se80.91799318.5 mβ to 81Br1/2
83Se82.91911922.3 mβ to 83Br9/2
84Se83.918473.3 mβ to 84Br0

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