Selenium (Se)

Metalloid element, belongs to group 16 of the periodic table. Multiple allotropic forms exist. Chemically resembles sulphur. Discovered in 1817 by Jons J. Berzelius.

Atomic Number	34
Atomic Weight	78.971
Mass Number	80

Group	16
Period	4
Block	p

Protons	34 p⁺
Neutrons	46 n⁰
Electrons	34 e^-

Properties

Energy
Atomic Radius	115 pm 224 pm
Molar Volume	16.5 cm³/mol
Covalent Radius	116 pm 107 pm 107 pm 117 pm 120 pm
Metallic Radius	117 pm 140 pm
Ionic Radius	198 pm 50 pm 28 pm 42 pm
Crystal Radius	184 pm 64 pm 42 pm 56 pm
Van der Waals Radius	190 pm 190 pm 403 pm 190 pm 229 pm 420.5 pm
Density	4.809 g/cm³ 3,990 kg/m³
Proton Affinity
Electron Affinity	2.02067 eV/particle
Ionization Energy	9.752392 eV/particle 21.196 eV/particle 31.697 eV/particle 42.947 eV/particle 68.3 eV/particle 81.827 eV/particle 155.33 eV/particle 184 eV/particle 219 eV/particle 255 eV/particle 291 eV/particle 342.9 eV/particle 383 eV/particle 426 eV/particle 473 eV/particle 517 eV/particle 650.5 eV/particle 693.38 eV/particle 739.8 eV/particle 798 eV/particle 845.8 eV/particle 887 eV/particle 989.6 eV/particle 1,036.362 eV/particle 2,540.7 eV/particle 2,674 eV/particle 2,820 eV/particle 2,964 eV/particle 3,146 eV/particle 3,301.8 eV/particle 3,507 eV/particle 3,636.526 eV/particle 15,367.4907 eV/particle 15,968.083 eV/particle
Heat of Vaporization	59.7 kJ/mol
Heat of Fusion	5.23 kJ/mol
Heat of Formation	227.2 kJ/mol
Electrons
Electron Shells	2, 8, 18, 6
Valence Electrons	6
Electron Configuration	[Ar] 3d¹⁰ 4s² 4p⁴
Oxidation States	-2, -1, 0, 1, 2, 3, 4, 5, 6
Electronegativity	14.34 eV/particle 0.2240328 2.55
Electrophilicity	2.2408492709619536 eV/particle
Phases
Phase	Solid
Gas Phase
Boiling Point	958.15 K 958.15 K
Melting Point	453.15 K 493.95 K
Critical Pressure	27.2 MPa
Critical Temperature	1,766.15 K 1,766.15 K
Triple Point
Visual
Color	Gray #ff1493 #ffa100 #ffa100
Appearance	black, red, and gray (not pictured) allotropes
Refractive Index	1.000895
Thermodynamic Properties
Thermal Conductivity	0.52 W/(m K)
Thermal Expansion
Molar Heat Capacity	25.363 J/(mol K)
Specific Heat Capacity	0.321 J/(g⋅K)
Heat Capacity Ratio (Adiabatic Index)
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
Magnetism
Type	diamagnetic
Magnetic Susceptibility (Mass)	-0.000000004 m³/Kg
Magnetic Susceptibility (Molar)	-0.000000000316 m³/mol
Magnetic Susceptibility (Volume)	-0.0000193
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal Structure	Simple Monoclinic (HEX)
Lattice Constant	4.36 Å
Lattice Angles	π/2, 1.58493, π/2
Mechanical Properties
Hardness	736 MPa 2 MPa
Bulk Modulus	8.3 GPa
Shear Modulus	3.7 GPa
Young Modulus	10 GPa
Poisson Ratio	0.33
Speed of Sound	3,350 m/s
Classification
Category	Other nonmetals, Nonmetals
CAS Group	VIB
IUPAC Group	VIA
Glawe Number	95
Mendeleev Number	101
Pettifor Number	93
Geochemical Class	semi-volatile
Goldschmidt Class	chalcophile
Other
Gas Basicity
Dipole Polarizability	28.9 ± 1 a₀
C6 Dispersion Coefficient	210 a₀ 233 a₀
Allotropes	Amorphous Red Selenium, Amorphous Black Selenium, Monoclinic Selenium, Hexagonal Selenium
Neutron Cross Section	11.7
Neutron Mass Absorption	0.0056
Quantum Numbers	3P2
Space Group	14 (P121/c1)

Isotopes of Selenium

Stable Isotopes	6
Unstable Isotopes	27
Radioactive Isotopes	28

⁶³Se

Abundance	Radioactive ☢️
Relative Atomic Mass	62.981911 ± 0.000537 Da
Mass Number	63
G-Factor
Half Life	13.2 ± 3.9 ms
Spin	3/2
Quadrupole Moment
Discovery Year	2016
Parity	-

⁶³Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	89%
2p (2-proton emission)	0.5%

⁶⁴Se

Abundance	Radioactive ☢️
Relative Atomic Mass	63.971165 ± 0.000537 Da
Mass Number	64
G-Factor	0
Half Life	22.6 ± 0.2 ms
Spin	0
Quadrupole Moment	0
Discovery Year	2005
Parity	+

⁶⁴Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%
β⁺ p (β⁺-delayed proton emission)	%

⁶⁵Se

Abundance	Radioactive ☢️
Relative Atomic Mass	64.964552 ± 0.000322 Da
Mass Number	65
G-Factor
Half Life	34.2 ± 0.7 ms
Spin	3/2
Quadrupole Moment
Discovery Year	1993
Parity	-

⁶⁵Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	87%

⁶⁶Se

Abundance	Radioactive ☢️
Relative Atomic Mass	65.955276 ± 0.000215 Da
Mass Number	66
G-Factor	0
Half Life	54 ± 4 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1993
Parity	+

⁶⁶Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	%

⁶⁷Se

Abundance	Radioactive ☢️
Relative Atomic Mass	66.949994 ± 0.000072 Da
Mass Number	67
G-Factor
Half Life	133 ± 4 ms
Spin	5/2
Quadrupole Moment
Discovery Year	1991
Parity	-

⁶⁷Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	0.5%

⁶⁸Se

Abundance	Radioactive ☢️
Relative Atomic Mass	67.941825236 ± 0.000000532 Da
Mass Number	68
G-Factor	0
Half Life	35.5 ± 0.7 s
Spin	0
Quadrupole Moment	0
Discovery Year	1990
Parity	+

⁶⁸Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%

⁶⁹Se

Abundance	Radioactive ☢️
Relative Atomic Mass	68.939414845 ± 0.000001599 Da
Mass Number	69
G-Factor
Half Life	27.4 ± 0.2 s
Spin	1/2
Quadrupole Moment	0
Discovery Year	1974
Parity	-

⁶⁹Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
β⁺ p (β⁺-delayed proton emission)	0.052%

⁷⁰Se

Abundance	Radioactive ☢️
Relative Atomic Mass	69.933515521 ± 0.0000017 Da
Mass Number	70
G-Factor	0
Half Life	41.1 ± 0.3 m
Spin	0
Quadrupole Moment	0
Discovery Year	1950
Parity	+

⁷⁰Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%

⁷¹Se

Abundance	Radioactive ☢️
Relative Atomic Mass	70.932209431 ± 0.000003 Da
Mass Number	71
G-Factor
Half Life	4.74 ± 0.05 m
Spin	5/2
Quadrupole Moment
Discovery Year	1957
Parity	-

⁷¹Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%

⁷²Se

Abundance	Radioactive ☢️
Relative Atomic Mass	71.927140506 ± 0.0000021 Da
Mass Number	72
G-Factor	0
Half Life	8.4 ± 0.08 d
Spin	0
Quadrupole Moment	0
Discovery Year	1948
Parity	+

⁷²Se Decay Modes

Decay Mode	Intensity
ϵ (electron capture)	100%

⁷³Se

Abundance	Radioactive ☢️
Relative Atomic Mass	72.926754881 ± 0.000007969 Da
Mass Number	73
G-Factor	0.19822222222222 ± 0.0028888888888889
Half Life	7.15 ± 0.09 h
Spin	9/2
Quadrupole Moment
Discovery Year	1948
Parity	+

⁷³Se Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%

⁷⁴Se

Abundance	0.86 ± 0.03
Relative Atomic Mass	73.922475933 ± 0.000000015 Da
Mass Number	74
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1922
Parity	+

⁷⁴Se Decay Modes

Decay Mode	Intensity
2β⁺ (double β⁺ decay)	%

⁷⁵Se

Abundance	Radioactive ☢️
Relative Atomic Mass	74.92252287 ± 0.000000078 Da
Mass Number	75
G-Factor	0.2732 ± 0.004
Half Life	119.78 ± 0.03 d
Spin	5/2
Quadrupole Moment	1.1 ± 0.2
Discovery Year	1947
Parity	+

⁷⁵Se Decay Modes

Decay Mode	Intensity
ϵ (electron capture)	100%

⁷⁶Se

Abundance	9.23 ± 0.07
Relative Atomic Mass	75.919213702 ± 0.000000017 Da
Mass Number	76
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1922
Parity	+

⁷⁷Se

Abundance	7.6 ± 0.07
Relative Atomic Mass	76.91991415 ± 0.000000067 Da
Mass Number	77
G-Factor	1.06712 ± 0.0001
Half Life
Spin	1/2
Quadrupole Moment	0
Discovery Year	1922
Parity	-

⁷⁸Se

Abundance	23.69 ± 0.22
Relative Atomic Mass	77.917309244 ± 0.000000191 Da
Mass Number	78
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1922
Parity	+

⁷⁹Se

Abundance	Radioactive ☢️
Relative Atomic Mass	78.918499252 ± 0.000000238 Da
Mass Number	79
G-Factor	-0.29085714285714 ± 0.0042857142857143
Half Life	327 ± 28 ky
Spin	7/2
Quadrupole Moment	0.8 ± 0.2
Discovery Year	1950
Parity	+

⁷⁹Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁸⁰Se

Abundance	49.8 ± 0.36
Relative Atomic Mass	79.916521761 ± 0.000001016 Da
Mass Number	80
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1922
Parity	+

⁸⁰Se Decay Modes

Decay Mode	Intensity
2β⁻ (double β⁻ decay)	%

⁸¹Se

Abundance	Radioactive ☢️
Relative Atomic Mass	80.917993019 ± 0.000001049 Da
Mass Number	81
G-Factor
Half Life	18.45 ± 0.12 m
Spin	1/2
Quadrupole Moment	0
Discovery Year	1948
Parity	-

⁸¹Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁸²Se

Abundance	Radioactive ☢️ 8.82 ± 0.15
Relative Atomic Mass	81.916699531 ± 0.0000005 Da
Mass Number	82
G-Factor	0
Half Life	87.6 ± 1.5 Ey
Spin	0
Quadrupole Moment	0
Discovery Year	1922
Parity	+

⁸²Se Decay Modes

Decay Mode	Intensity
2β⁻ (double β⁻ decay)	100%

⁸³Se

Abundance	Radioactive ☢️
Relative Atomic Mass	82.919118604 ± 0.000003259 Da
Mass Number	83
G-Factor
Half Life	22.25 ± 0.04 m
Spin	9/2
Quadrupole Moment
Discovery Year	1937
Parity	+

⁸³Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁸⁴Se

Abundance	Radioactive ☢️
Relative Atomic Mass	83.918466761 ± 0.000002105 Da
Mass Number	84
G-Factor	0
Half Life	3.26 ± 0.1 m
Spin	0
Quadrupole Moment	0
Discovery Year	1960
Parity	+

⁸⁴Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁸⁵Se

Abundance	Radioactive ☢️
Relative Atomic Mass	84.922260758 ± 0.000002804 Da
Mass Number	85
G-Factor
Half Life	32.9 ± 0.3 s
Spin	5/2
Quadrupole Moment
Discovery Year	1960
Parity

⁸⁵Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%

⁸⁶Se

Abundance	Radioactive ☢️
Relative Atomic Mass	85.924311732 ± 0.000002705 Da
Mass Number	86
G-Factor	0
Half Life	14.3 ± 0.3 s
Spin	0
Quadrupole Moment	0
Discovery Year	1973
Parity	+

⁸⁶Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	%

⁸⁷Se

Abundance	Radioactive ☢️
Relative Atomic Mass	86.928688616 ± 0.000002405 Da
Mass Number	87
G-Factor
Half Life	5.5 ± 0.06 s
Spin	3/2
Quadrupole Moment
Discovery Year	1968
Parity	+

⁸⁷Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	0.6%

⁸⁸Se

Abundance	Radioactive ☢️
Relative Atomic Mass	87.93141749 ± 0.000003604 Da
Mass Number	88
G-Factor	0
Half Life	1.53 ± 0.06 s
Spin	0
Quadrupole Moment	0
Discovery Year	1970
Parity	+

⁸⁸Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	0.99%

⁸⁹Se

Abundance	Radioactive ☢️
Relative Atomic Mass	88.936669058 ± 0.000004003 Da
Mass Number	89
G-Factor
Half Life	430 ± 50 ms
Spin	5/2
Quadrupole Moment
Discovery Year	1971
Parity	+

⁸⁹Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	7.8%

⁹⁰Se

Abundance	Radioactive ☢️
Relative Atomic Mass	89.940096 ± 0.000354 Da
Mass Number	90
G-Factor	0
Half Life	210 ± 80 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1994
Parity	+

⁹⁰Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	%

⁹¹Se

Abundance	Radioactive ☢️
Relative Atomic Mass	90.9457 ± 0.000465 Da
Mass Number	91
G-Factor
Half Life	270 ± 50 ms
Spin	1/2
Quadrupole Moment	0
Discovery Year	1975
Parity	+

⁹¹Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	21%
2n (2-neutron emission)	%

⁹²Se

Abundance	Radioactive ☢️
Relative Atomic Mass	91.94984 ± 0.000429 Da
Mass Number	92
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1997
Parity	+

⁹²Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

⁹³Se

Abundance	Radioactive ☢️
Relative Atomic Mass	92.956135 ± 0.000429 Da
Mass Number	93
G-Factor
Half Life
Spin	1/2
Quadrupole Moment	0
Discovery Year	1997
Parity	+

⁹³Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

⁹⁴Se

Abundance	Radioactive ☢️
Relative Atomic Mass	93.96049 ± 0.000537 Da
Mass Number	94
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1997
Parity	+

⁹⁴Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

⁹⁵Se

Abundance	Radioactive ☢️
Relative Atomic Mass	94.9673 ± 0.000537 Da
Mass Number	95
G-Factor
Half Life
Spin	3/2
Quadrupole Moment
Discovery Year	2010
Parity	+

⁹⁵Se Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	%
β⁻ n (β⁻-delayed neutron emission)	%
2n (2-neutron emission)	%

History

Selenium was first observed in about the year 1300 by the alchemist Arnold of Villanova. Selenium was discovered in 1817 by Jöns Jacob Berzelius and Johan Gottlieb Gahn who noted the similarity of the new element to the previously-known tellurium. In 1873, Willoughby Smith found that the electrical resistance of grey selenium was dependent on the ambient light. From the Greek word Selene, moon

Discoverers	Jöns Berzelius
Discovery Location	Sweden
Discovery Year	1818
Etymology (Name Origin)	Greek: selênê (moon).
Pronunciation	si-LEE-ni-em (English)

Many of selenium's compounds, such as selenates and selenites, are highly toxic

Selenium deficiency in animals can lead to slow growth

Uses

Selenium is used in the glass industry to decolorize glass and to make red-colored glasses and enamels. It is used as a catalyst in many chemical reactions. It is also used as a photographic toner, and as an additive to stainless steel. Selenium sulfide is used in anti-dandruff shampoos. Light causes it to conduct electricity more easily. It is used in photoelectric cells, TV cameras, xerography machines and as a semiconductor in solar batteries and rectifiers. Also colors glass red.

Sources

Obtained from lead, copper and nickel refining. Conducts electricity when struck by light.

Abundance
Abundance in Earth's crust	0.05 mg/kg
Abundance in Oceans	0.0002 mg/L
Abundance in Human Body	0.000005 %
Abundance in Meteor	0.0013 %
Abundance in Sun
Abundance in Universe	0.000003 %

Nuclear Screening Constants

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

Selenium on ChemicalAid

Art & Architecture Thesaurus ID	300156319
Australian Educational Vocabulary ID	scot/3574
BNCF Thesaurus ID	52421
Biblioteca Nacional de España ID	XX534324
Bibliothèque nationale de France ID	121383271
Brockhaus Enzyklopädie online ID	selen
CAS Registry Number	7782-49-2
ChEBI ID	27568
ChemSpider ID	4885617
DSSTOX compound identifier	DTXCID701261
DSSTox substance ID	DTXSID9021261
Den Store Danske ID	selen
DrugBank ID	11135
ECHA Substance Infocard ID	100.029.052
Encyclopædia Britannica Online ID	science/selenium
Encyclopædia Universalis ID	selenium
Freebase ID	/m/025sf8g
French Vikidia ID	Sélénium
GND ID	4180872-1
Gran Enciclopèdia Catalana ID	0238414
Great Russian Encyclopedia Online ID	3546300
HCIS ID	4102
HSDB ID	4493
Human Metabolome Database ID	HMDB0001349
ICSC ID	0072
InChI	InChI=1S/Se
InChIKey	BUGBHKTXTAQXES-UHFFFAOYSA-N
KBpedia ID	Selenium
KEGG ID	C01529
Library of Congress authority ID	sh85119688
MeSH descriptor ID	D012643
MinDat mineral ID	37996
MinDat mineral ID	3611
NALT ID	33437
NDF-RT ID	N0000148196
NKCR AUT ID	ph127055
National Diet Library ID	00570819
National Library of Israel J9U ID	987007529471405171
OmegaWiki Defined Meaning	3373
OpenAlex ID	C553756173
PSH ID	5808
PatientsLikeMe treatment ID	selenium
PubChem CID	6326970
Quora topic ID	Selenium-2
Quora topic ID	Selenium-element
RxNorm ID	9641
Store medisinske leksikon ID	selen
Store norske leksikon ID	selen
Treccani ID	selenio
UK Archival Thesaurus ID	f2/mt225/4347/9119
UMLS CUI	C0036581
UNII	H6241UJ22B
WikiSkripta ID	12122
Wolfram Language entity code	Entity["Mineral", "Selenium"]
WordNet 3.1 Synset ID	14678354-n
YSO ID	10413
ZVG number	7340

Selenium (Se)

Properties

Isotopes of Selenium

63Se

63Se Decay Modes

64Se

64Se Decay Modes

65Se

65Se Decay Modes

66Se

66Se Decay Modes

67Se

67Se Decay Modes

68Se

68Se Decay Modes

69Se

69Se Decay Modes

70Se

70Se Decay Modes

71Se

71Se Decay Modes

72Se

72Se Decay Modes

73Se

73Se Decay Modes

74Se

74Se Decay Modes

75Se

75Se Decay Modes

76Se

77Se

78Se

79Se

79Se Decay Modes

80Se

80Se Decay Modes

81Se

81Se Decay Modes

82Se

82Se Decay Modes

83Se

83Se Decay Modes

84Se

84Se Decay Modes

85Se

85Se Decay Modes

86Se

86Se Decay Modes

87Se

87Se Decay Modes

88Se

88Se Decay Modes

89Se

89Se Decay Modes

90Se

90Se Decay Modes

91Se

91Se Decay Modes

92Se

92Se Decay Modes

93Se

93Se Decay Modes

94Se

94Se Decay Modes

95Se

95Se Decay Modes