Periodic Table/Selenium
← AsBr →
34Se78.9710 Da

Selenium

Nonmetal·Period 4, Group 16·p-block

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

Gallery

Ultrapure Black, Amorphous Selenium, 3 - 4 grams. Original size in cm: 2

Hi-Res Images ofChemical Elements, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/selenium.php

Bohr model of Selenium

Physical Propertiesmass · density · phase · crystal

Atomic Mass

78.9710Da

Density

4.8090g/cm³

Phase (STP)

Solid

Melting Point

—

Boiling Point

958.1K

Molar Heat

0.3210J/(mol·K)

Crystal Structure

HEX

Lattice Constant

4.360Å

Atomic Radiiatomic · covalent · van der Waals

Atomic (Empirical)

115.00pm

Covalent

116.00pm

Van der Waals

190.00pm

Electronic Propertieselectronegativity · ionization · affinity

Electron Configuration

[Ar] 3d10 4s2 4p4

Electron Shells

2, 8, 18, 6

Electronegativity

2.55Pauling

Electron Affinity

2.0kJ/mol

1st Ionization Energy

9.8kJ/mol

Oxidation States

-2, +2, +4, +6

Orbital DiagramAufbau · Hund's rule · Pauli exclusion

↑↓
1s2
↑↓
2s2
↑↓
↑↓
↑↓
2p6
↑↓
3s2
↑↓
↑↓
↑↓
3p6
↑↓
↑↓
↑↓
↑↓
↑↓
3d10
↑↓
4s2
↑↓
↑
↑
4p4

Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4Short: [Ar] 3d10 4s2 4p4

Ionization Energies (34 known)

1st9.8 kJ/mol2nd21.2 kJ/mol3rd31.7 kJ/mol4th42.9 kJ/mol5th68.3 kJ/mol6th81.8 kJ/mol7th155.3 kJ/mol8th184.0 kJ/mol9th219.0 kJ/mol10th255.0 kJ/mol11th291.0 kJ/mol12th342.9 kJ/mol13th383.0 kJ/mol14th426.0 kJ/mol15th473.0 kJ/mol16th517.0 kJ/mol17th650.5 kJ/mol18th693.4 kJ/mol19th739.8 kJ/mol20th798.0 kJ/mol21th845.8 kJ/mol22th887.0 kJ/mol23th989.6 kJ/mol24th1036.4 kJ/mol25th2540.7 kJ/mol26th2674.0 kJ/mol27th2820.0 kJ/mol28th2964.0 kJ/mol29th3146.0 kJ/mol30th3301.8 kJ/mol31th3507.0 kJ/mol32th3636.5 kJ/mol33th15367.5 kJ/mol34th15968.1 kJ/molSuccessive Ionization Energies

Emission Spectrumvisible range · characteristic spectral lines

474
474
523
448
Se emission
380nm750nm
522.5 nm(100%)473.9 nm(50%)474.2 nm(40%)448.1 nm(30%)

Abundanceby mass

🌍Earth's Crust
50.0 ppb
🌊Ocean
90.0 ppt
✨Universe
90.0 ppb
🧬Human Body
50.0 ppb

Log scale · ppm = parts per million by mass

Biological Role

Essential (trace)

Component of selenocysteine amino acid. Antioxidant role in glutathione peroxidase.

Discovery

Discovered By

Jöns Berzelius

Named By

—

Year

1818

Nuclear Data

Known Isotopes

33

Stable Isotopes

5

Stable Mass Numbers

74, 76, 77, 78, 80

Natural isotopic abundance (IUPAC recommended values)

Isotopes of Se33 known

NuclideZNMass (AMU)Half-lifeDecayJπAbundance
63Se342962.98191113.2 msβ⁺ (1%), β⁺p (0.89%), 2p (0.005%)3/2-—
64Se343063.97116522.6 msβ⁺, β⁺p0+—
65Se343164.96455234.2 msβ⁺ (1%), β⁺p (0.87%)3/2-—
74Sestable344073.922476Stable2β⁺0+86.0000%
76Sestable344275.919214Stablestable (1%)0+923.0000%
77Sestable344376.919914Stablestable (1%)1/2-760.0000%
78Sestable344477.917309Stablestable (1%)0+2369.0000%
80Sestable344679.916522Stable2β⁻0+4980.0000%
82Se344881.91670087600000000 Gy2β⁻ (1%)0+882.0000%
93Se345992.956135Unknownβ⁻, β⁻n, 2n1/2+—
94Se346093.960490Unknownβ⁻, β⁻n, 2n0+—
95Se346194.967300Unknownβ⁻, β⁻n, 2n3/2+—

Click any isotope for its full page with decay chain:

63Se64Se65Se66Se67Se68Se69Se70Se71Se72Se73Se74Se75Se76Se77Se78Se79Se80Se81Se82Se83Se84Se85Se86Se87Se88Se89Se90Se91Se92Se93Se94Se95Se
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