Selenium

Chemical, physical and material properties and data of the chemical element Selenium.

Contents

General Information about Selenium

Regular nameSeleniumChemical symbolSeOther namesHistorical namesName meaning, originDiscovery (year)OccurencePosition in the PSEGroup membership

Atomar Properties of Selenium

Atomic number Z34 = number of protonsStandard Atomic Weight78.971 (8)

Electron configuration of Selenium

1s	2s	2p	3s	3p	3d	4s	4p	4d	4f	5s	5p	5d	5f	6s	6p	6d	6f	7s	7p
2	2	6	2	6	10	2	4

Shorthand electron configuration of Selenium: [Ar] 3d¹⁰ 4s² 4p⁴ .

Ionization Energies of Selenium

The following table lists the ionization energies IE (ionization potentials); the IE is the energy required in electron volt (eV) per atom to separate a given electron from an Selenium atom.

IE1	IE2	IE3	IE4	IE5	IE6	IE7
9.75239	21.19	30.8204	42.9450	68.3	81.70	155.4

Isotopic Data of Selenium

An overview of the nuclides as well as the isotopic data and properties are listed on the following page: Selenium isotopes.

Chemistry of Selenium

Oxidation states-2. +2. +4. +6Electronegativity2.4 (Pauling original)
2.55 (Pauling)
2.434 (Allen)
2.4 (Mulliken)
2.76 (Sanderson)
2.48 (Allred-Rochow)
5.8746 eV (Gosh Gupta)
5.89 eV (Pearson)Electron affinity2.020 604 7(12) eV
194.958 7(2) kJ mol^-1

Standard Electrode Potential

E⁰ (V)	Symbol	N_ox	Name Ox. Name Red.	Ox. Red.	e^-
-0.670	Se	0 - II	Selenium Selenium anion	Se ⇄ Se^2-	+ 2 e^-
-0.399	Se	0 - II	Selenium Hydrogen selenide	Se (s) + 2 H⁺ ⇄ H₂Se (aq)	+ 2 e^-
0.74	Se	+ IV 0	Selenous acid Selenium	H₂SeO₃ + 4 H⁺ ⇄ Se + 3 H₂O	+ 4 e^-
0.74	Se	+ IV 0	Selenous acid Selenium	H₂SeO₃ (aq) + 4 H⁺ ⇄ Se (s) + 3 H₂O	+ 4 e^-
1.15	Se	+ VI + IV	Hydrogenselenite anion Selenous acid	HSeO₄^- + 3 H⁺ ⇄ H₂SeO₃ (aq) + H₂O	+ 2 e^-

Material and Physical Properties

Melting point220.8 °CEnthalpy of fusion (molar)6.69 kJ mol^-1Boiling point685 °CEnthalpy of vaporization26.32 kJ mol^-1Density4.81 g cm^-3

External Data, Identifiers

CAS registry number7782-49-2InChI =1S/SeInChIKeyBUGBHKTXTAQXES-UHFFFAOYSA-NPubChem ID6326970

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Last update: 2022-12-12

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