Selenium

Last updated: May 12, 2022

Selenium is an elementary substance of main group element with formula Se.

Table of contents

Names

List of substance names

Nomenclature

Name

Typical name: Selenium

Compositional nomenclature: Selenium

Formulae and structures

List of formulae

Formula name

Formula

Typical formula: Se

Molecular formula: Se₈
Red selenium

Compositional formula: Se

Structural formula: Gray selenium; Red selenium

Properties

List of substance properties

Item

Value

Name: Selenium

Formula: Se

Appearance: Gray solid
Gray selenium; Red solid
Red selenium; Black solid
Vitreous selenium

Odor: Odorless

Molar mass: 78.971 g/mol

Density: 4.81 g/cm³^[1]
Solid, 20°C, Gray selenium; 4.809 g/cm³^[2]
Solid, Gray selenium; 4.39 g/cm³^[2]
Solid, Red selenium; 4.28 g/cm³^[2]
Solid, Vitreous selenium

Melting point: 217 °C^[1]
Gray selenium; 220.8 °C^[2]
Gray selenium; >120 °C^[2]
Red selenium, transition to gray selenium; >180 °C^[2]
Vitreous selenium, transition to gray selenium

Boiling point: 685 °C^[1]
Gray selenium; 685 °C^[2]

Constituents

Constituent atoms

Atom	Name	Oxidation state	Number
Se	Selenium	0	1

Ratio of atoms

Atom	Atomic weight	Number	Atomic ratio	Weight ratio
Se	78.971	1	100.00%	100.00%

Thermodynamic properties

Phase transition properties

Item

Value

Enthalpy of fusion: 6.69 kJ · mol⁻¹^[1][2]
at 217°C

Enthalpy of vaporization: 95.48 kJ · mol⁻¹^[1][2]
at 685°C

Enthalpy of vaporization at 25°C: –

Enthalpy of other transition: 0.75 kJ · mol⁻¹^[1]
at 150°C

Standard thermodynamic properties

State	Standard enthalpy of formation Δ_fH° kJ · mol⁻¹	Standard Gibbs energy of formation Δ_fG° kJ · mol⁻¹	Standard molar entropy S° J · K⁻¹ · mol⁻¹	Standard molar heat capacity at constant pressure C_p° J · K⁻¹ · mol⁻¹
Crystalline solid hexagonal, gray	0^[3]	0^[3]	42.442^[3]	25.363^[3]
Crystalline solid monoclinic, red	6.7^[3]	–	–	–
Vitreous liquid	5.0^[3]	–	–	–
Gas	227.07^[3]	187.03^[3]	176.72^[3]	20.820^[3]

Solubility

Qualitative solubility

Reactive

Miscible

Very soluble

Soluble: CH₂I₂Diiodomethane
C₂H₅OC₂H₅^[1]Diethyl ether
KOH (aq)^[1]Potassium hydroxide solution
KCN (aq)^[1]Potassium cyanide solution

Slightly soluble

Very slightly soluble: CS₂Carbon disulfide

Insoluble: H₂O^[1]Water
C₂H₅OH^[1]Ethanol
CS₂^[4]Carbon disulfide

Solubility in diiodomethane (g/100 g)^[4]

12°C
1.3

Solubility in carbon disulfide (g/100 mL, Vitreous selenium)^[4]

20°C
0.065

Solubility curve (g/100 g)

Solubility curve (g/100 mL)

Hazards

GHS label^[5]

Item

Value

Hazard pictograms: GHS08: Health hazard

Signal word: Danger

Hazard statements: H370: Causes damage to organs; H370: Causes damage to central nervous system; H370: Causes damage to respiratory system; H370: Causes damage to cardiovascular system; H370: Causes damage to gastrointestinal tract; H372: Causes damage to organs through prolonged or repeated exposure; H372: Causes damage to nervous system through prolonged or repeated exposure; H372: Causes damage to respiratory system through prolonged or repeated exposure; H372: Causes damage to liver through prolonged or repeated exposure; H413: May cause long harmful effects to aquatic life

Physical hazards^[5]

Classification	Category	Label	Hazard statement
Explosives	Not applicable
Flammable gases	Not applicable
Aerosols	Not applicable
Oxidizing gases	Not applicable
Gases under pressure	Not applicable
Flammable liquids	Not applicable
Flammable solids	Not classified
Self reactive substances and mixtures	Not applicable
Pyrophoric liquids	Not applicable
Pyrophoric solids	Not classified
Self heating substances and mixtures	Not classified
Substances and mixtures which in contact with water emit flammable gases	Not classified
Oxidizing liquids	Not applicable
Oxidizing solids	Not applicable
Organic peroxides	Not applicable
Substances and mixtures corrosive to metals	Classification not possible
Desensitized explosives	No data

Health hazards^[5]

Classification	Category	Label	Hazard statement
Acute oral toxicity	Not classified
Acute dermal toxicity	Classification not possible
Acute inhalation toxicity by gas	Not applicable
Acute inhalation toxicity by vapor	Not applicable
Acute inhalation toxicity by dust or mist	Classification not possible
Skin corrosion irritation	Classification not possible
Serious eye damage eye irritation	Classification not possible
Respiratory sensitization	Classification not possible
Skin sensitization	Classification not possible
Germ cell mutagenicity	Classification not possible
Carcinogenicity	Classification not possible
Reproductive toxicity	Classification not possible
Specific target organ toxicity single exposure	Category 1 (Central nervous system, Respiratory system, Cardiovascular system, Gastrointestinal tract)	Danger	H370: Causes damage to organs H370: Causes damage to central nervous system H370: Causes damage to respiratory system H370: Causes damage to cardiovascular system H370: Causes damage to gastrointestinal tract
Specific target organ toxicity repeated exposure	Category 1 (Nervous system, Respiratory system, Liver)	Danger	H372: Causes damage to organs through prolonged or repeated exposure H372: Causes damage to nervous system through prolonged or repeated exposure H372: Causes damage to respiratory system through prolonged or repeated exposure H372: Causes damage to liver through prolonged or repeated exposure
Aspiration hazard	Classification not possible

Environmental hazards^[5]

Classification	Category	Hazard statement
Hazardous to the aquatic environment short term	Classification not possible
Hazardous to the aquatic environment long term	Category 4	H413: May cause long harmful effects to aquatic life
Hazardous to the ozone layer	No data

Preparations

Reaction of reducing nonmetal and oxide

The reaction of reducing nonmetal and oxide can yield selenium.

Reaction of hydrogen and selenium dioxide: 2H₂Hydrogen + SeO₂Selenium dioxide
🔥
⟶
SeSelenium + 2H₂OWater

Reaction of carbon and selenium dioxide: CCarbon + SeO₂Selenium dioxide
🔥
⟶
SeSelenium + CO₂↑Carbon dioxide

Reaction of carbon and selenium dioxide: 2CCarbon + SeO₂Selenium dioxide
🔥
⟶
SeSelenium + 2CO↑Carbon monoxide

Reaction of hydrogen and selenium trioxide: 3H₂Hydrogen + SeO₃Selenium trioxide
🔥
⟶
SeSelenium + 3H₂OWater

Reaction of carbon and selenium trioxide: 3CCarbon + 2SeO₃Selenium trioxide
🔥
⟶
2SeSelenium + 3CO₂↑Carbon dioxide

Decomposition

Decomposition of thermally decomposable substance can yield selenium.

Decomposition of iron(II) selenide: FeSeIron(II) selenide
🔥
⟶
FeIron + SeSelenium

Decomposition of selenous acid: 2H₂SeO₃Selenous acid
🔥
⟶
SeSelenium + 2H₂O₂Hydrogen peroxide + SeO₂Selenium dioxide

Decomposition of selenium trioxide: 2SeO₃Selenium trioxide
🔥
⟶
2SeSelenium + 3O₂↑Oxygen

Decomposition of selenous acid ◆ Δ_rG 189.01 kJ/mol K 0.77 × 10⁻³³ pK 33.11: H₂SeO₃Selenous acid
🔥
⟶
SeSelenium + O₂↑Oxygen + H₂OWater

Decomposition of sodium selenite ◆ Δ_rG 518.2 kJ/mol K 0.16 × 10⁻⁹⁰ pK 90.78: Na₂SeO₃Sodium selenite
🔥
⟶
Na₂OSodium oxide + SeSelenium + O₂↑Oxygen

Chemical reactions

Reaction with metal

The reaction of metal and selenium yields binary compound of selenium.

Reaction of sodium and selenium ◆ Δ_rG −394.6 kJ/mol K 1.35 × 10⁶⁹ pK −69.13: 2NaSodium + SeSelenium
⟶
Na₂SeSodium selenide

Reaction of potassium and selenium ◆ Δ_rG −437.2 kJ/mol K 3.93 × 10⁷⁶ pK −76.59: 2KPotassium + SeSelenium
⟶
K₂SePotassium selenide

Reaction of calcium and selenium ◆ Δ_rG −363.2 kJ/mol K 4.26 × 10⁶³ pK −63.63: CaCalcium + SeSelenium
⟶
CaSeCalcium selenide

Reaction of iron and selenium: FeIron + SeSelenium
⟶
FeSeIron(II) selenide

Reaction with nonmetal

The reaction of selenium and nonmetal yields binary compound of selenium.

Reaction of hydrogen and selenium ◆ Δ_rG 15.9 kJ/mol K 0.16 × 10⁻² pK 2.79: H₂Hydrogen + SeSelenium
🔥
⟶
H₂SeHydrogen selenide

Reaction of selenium and oxygen: SeSelenium + O₂Oxygen
⟶
SeO₂Selenium dioxide

Reaction of selenium and ozone: 3SeSelenium + 2O₃Ozone
⟶
3SeO₂Selenium dioxide

Reaction of selenium and oxygen: 2SeSelenium + 3O₂Oxygen
⟶
2SeO₃Selenium trioxide

Reaction of selenium and ozone: SeSelenium + O₃Ozone
⟶
SeO₃Selenium trioxide

Reaction with water

The reaction of selenium and water yields oxoacid and hydride.

Reaction of selenium and water ◆ Δ_rG 317.0 kJ/mol K 0.29 × 10⁻⁵⁵ pK 55.54: 3SeSelenium + 3H₂OWater
🔥
⟶
H₂SeO₃Selenous acid + 2H₂Se↑Hydrogen selenide

Reaction of selenium and water: 4SeSelenium + 4H₂OWater
⟶
H₂SeO₄Selenic acid + 3H₂Se↑Hydrogen selenide

Reaction with hydroxide base

The reaction of selenium and hydroxide base yields oxoacid salt, salt of hydracid/hydride, and oxide.

Reaction of selenium and sodium hydroxide ◆ Δ_rG 120.6 kJ/mol K 0.74 × 10⁻²¹ pK 21.13: 3SeSelenium + 6NaOHSodium hydroxide
🔥
⟶
Na₂SeO₃Sodium selenite + 2Na₂SeSodium selenide + 3H₂OWater

Reaction of selenium and potassium hydroxide ◆ Δ_rG 120.9 kJ/mol K 0.66 × 10⁻²¹ pK 21.18: 3SeSelenium + 6KOHPotassium hydroxide
🔥
⟶
K₂SeO₃Potassium selenite + 2K₂SePotassium selenide + 3H₂OWater

Reaction of selenium and calcium hydroxide: 3SeSelenium + 3Ca(OH)₂Calcium hydroxide
⟶
CaSeO₃Calcium selenite + 2CaSeCalcium selenide + 3H₂OWater

Reaction of selenium and sodium hydroxide ◆ Δ_rG 255.7 kJ/mol K 0.16 × 10⁻⁴⁴ pK 44.80: 4SeSelenium + 8NaOHSodium hydroxide
🔥
⟶
Na₂SeO₄Sodium selenate + 3Na₂SeSodium selenide + 4H₂OWater

Reaction of selenium and potassium hydroxide ◆ Δ_rG 256.0 kJ/mol K 0.14 × 10⁻⁴⁴ pK 44.85: 4SeSelenium + 8KOHPotassium hydroxide
🔥
⟶
K₂SeO₄Potassium selenate + 3K₂SePotassium selenide + 4H₂OWater

Reaction with reducing species

The reaction of hydrogen sulfide and selenium yields sulfur and hydrogen selenide.

Reaction of hydrogen sulfide and selenium ◆ Δ_rG 49.5 kJ/mol K 0.21 × 10⁻⁸ pK 8.67: H₂SHydrogen sulfide + SeSelenium
🔥
⟶
SSulfur + H₂SeHydrogen selenide

Reaction with oxidizing species

The reaction of selenium and oxidizing species yields a variety of products.

Reaction of selenium and potassium permanganate ◆ Δ_rG −457.9 kJ/mol K 1.66 × 10⁸⁰ pK −80.22: SeSelenium + 2KMnO₄Potassium permanganate
⟶
K₂SeO₄Potassium selenate + 2MnO₂Manganese(IV) oxide

Reaction of selenium and nitric acid ◆ Δ_rG −64.18 kJ/mol K 1.75 × 10¹¹ pK −11.24: SeSelenium + 2HNO₃Nitric acid
⟶
H₂SeO₃Selenous acid + N₂O₃↑Dinitrogen trioxide

Reaction of selenium and nitric acid ◆ Δ_rG −13.03 kJ/mol K 1.92 × 10² pK −2.28: SeSelenium + 4HNO₃Nitric acid
🔥
⟶
H₂SeO₃Selenous acid + 4NO₂↑Nitrogen dioxide + H₂OWater

Reaction with oxidizing species under acidic condition

The reaction of selenium, oxidizing species, and hydrogen ion yields a variety of products.

Reaction of selenium and potassium permanganate under acidic condition ◆ Δ_rG −1491.3 kJ/mol K 1.84 × 10²⁶¹ pK −261.26: 5SeSelenium + 4KMnO₄Potassium permanganate + 12H⁺Hydrogen ion
⟶
5H₂SeO₃Selenous acid + 4Mn²⁺Manganese(II) ion + 4K⁺Potassium ion + H₂OWater

Reaction of selenium and potassium permanganate under acidic condition ◆ Δ_rG −1378.5 kJ/mol K 3.18 × 10²⁴¹ pK −241.50: 5SeSelenium + 4KMnO₄Potassium permanganate + 8H⁺Hydrogen ion
⟶
2K₂SeO₃Potassium selenite + 3H₂SeO₃Selenous acid + 4Mn²⁺Manganese(II) ion + H₂OWater

Reaction with oxidizing species under neutral condition

The reaction of selenium, oxidizing species, and water yields a variety of products.

Reaction of selenium and potassium permanganate under neutral condition ◆ Δ_rG −1000.2 kJ/mol K 1.69 × 10¹⁷⁵ pK −175.23: 3SeSelenium + 4KMnO₄Potassium permanganate + H₂OWater
⟶
2K₂SeO₃Potassium selenite + H₂SeO₃Selenous acid + 4MnO₂Manganese(IV) oxide

Reaction of selenium and oxygen under neutral condition ◆ Δ_rG −205.4 kJ/mol K 9.65 × 10³⁵ pK −35.98: SeSelenium + O₂Oxygen + H₂OWater
⟶
H₂SeO₃Selenous acid

Reaction of selenium and chlorine under neutral condition ◆ Δ_rG −109.83 kJ/mol K 1.74 × 10¹⁹ pK −19.24: SeSelenium + 2Cl₂Chlorine + 3H₂OWater
⟶
H₂SeO₃Selenous acid + 4HClHydrogen chloride

Reaction of selenium and oxygen under neutral condition: 2SeSelenium + 3O₂Oxygen + 2H₂OWater
⟶
2H₂SeO₄Selenic acid

Reaction of selenium and chlorine under neutral condition: SeSelenium + 3Cl₂Chlorine + 4H₂OWater
⟶
H₂SeO₄Selenic acid + 6HClHydrogen chloride

Reaction with oxidizable species

The reaction of potassium iodide and selenium yields potassium selenide and iodine.

Reaction of potassium iodide and selenium ◆ Δ_rG 248.9 kJ/mol K 0.25 × 10⁻⁴³ pK 43.61: 2KIPotassium iodide + SeSelenium
🔥
⟶
K₂SePotassium selenide + I₂Iodine

References

List of references

1
James G. Speight (2017)
Lange's Handbook of Chemistry, 17th edition
https://www.accessengineeringlibrary.com/content/book/9781259586095
McGraw Hill Education
- Amazon
Citation list
- ^ Density, 4.81 g/cm³ - p.61
- ^ Melting point, 217 °C - p.61
- ^ Boiling point, 685 °C - p.61
- ^ Enthalpy of fusion, 6.69 kJ · mol⁻¹ - p.309
- ^ Enthalpy of vaporization, 95.48 kJ · mol⁻¹ - p.309
- ^ Enthalpy of other transition, 0.75 kJ · mol⁻¹ - p.309
- ^ Qualitative solubility, Soluble in diethyl ether - p.61
- ^ Qualitative solubility, Soluble in potassium hydroxide solution - p.61
- ^ Qualitative solubility, Soluble in potassium cyanide solution - p.61
- ^ Qualitative solubility, Insoluble in water - p.61
- ^ Qualitative solubility, Insoluble in ethanol - p.61
2
John R. Rumble Jr, David R. Lide, Thomas J. Bruno (2019)
CRC Handbook of Chemistry and Physics 100th Edition
https://www.routledge.com/CRC-Handbook-of-Chemistry-and-Physics/book-series/CRCHANCHEPHY
CRC Press
- Amazon
Citation list
- ^ Density, 4.809 g/cm³ - p.4-48
- ^ Density, 4.39 g/cm³ - p.4-48
- ^ Density, 4.28 g/cm³ - p.4-48
- ^ Melting point, 220.8 °C - p.4-48
- ^ Melting point, >120 °C - p.4-48
- ^ Melting point, >180 °C - p.4-48
- ^ Boiling point, 685 °C - p.4-48
- ^ Enthalpy of fusion, 6.69 kJ · mol⁻¹ - p.6-160
- ^ Enthalpy of vaporization, 95.48 kJ · mol⁻¹ - p.6-160
3
Janiel J. Reed (1989)
The NBS Tables of Chemical Thermodynamic Properties: Selected Values for Inorganic and C1 and C2 Organic Substances in SI Units
https://doi.org/10.18434/M32124
National Institute of Standards and Technology (NIST)
Citation list
4
Atherton Seidell (1919)
Solubilities of Inorganic and Organic Compounds: A Compilation of Quantitative Solubility Data From the Periodical Literature
D. Van Nostrand Company
- Amazon
Citation list
5
Chemical Management Center
GHS Classification Results
https://www.nite.go.jp/chem/english/ghs/all_fy_e.html
National Institute of Technology and Evaluation
Citation list

Δ_rG	189.01 kJ/mol
K	0.77 × 10⁻³³
pK	33.11

Δ_rG	518.2 kJ/mol
K	0.16 × 10⁻⁹⁰
pK	90.78

Δ_rG	−394.6 kJ/mol
K	1.35 × 10⁶⁹
pK	−69.13

Δ_rG	−437.2 kJ/mol
K	3.93 × 10⁷⁶
pK	−76.59

Selenium

Names

List of substance names

Formulae and structures

List of formulae

Properties

List of substance properties

Constituents

Constituent atoms

Ratio of atoms

Thermodynamic properties

Phase transition properties

Standard thermodynamic properties

Solubility

Qualitative solubility

Solubility in diiodomethane (g/100 g)[4]

Solubility in carbon disulfide (g/100 mL, Vitreous selenium)[4]

Solubility curve (g/100 g)

Solubility curve (g/100 mL)

Hazards

GHS label[5]

Physical hazards[5]

Health hazards[5]

Environmental hazards[5]

Preparations

Reaction of reducing nonmetal and oxide

Decomposition

Chemical reactions

Reaction with metal

Reaction with nonmetal

Reaction with water

Reaction with hydroxide base

Reaction with reducing species

Reaction with oxidizing species

Reaction with oxidizing species under acidic condition

Reaction with oxidizing species under neutral condition

Reaction with oxidizable species

References

List of references

Related substances

Elementary substances of group 16 element

Selenium compounds

Related categories

Solubility in diiodomethane (g/100 g)^[4]

Solubility in carbon disulfide (g/100 mL, Vitreous selenium)^[4]

GHS label^[5]

Physical hazards^[5]

Health hazards^[5]

Environmental hazards^[5]