Boron

Last updated: March 31, 2022

Boron is an elementary substance of main group element with formula B.

Table of contents

Names

List of substance names

Nomenclature

Name

Typical name: Boron

Compositional nomenclature: Boron

Formulae and structures

List of formulae

Formula name

Formula

Typical formula: B

Compositional formula: B

Structural formula

Properties

List of substance properties

Item

Value

Name: Boron

Formula: B

Appearance: Black brown solid

Odor: Odorless

Molar mass: 10.81 g/mol

Density: 2.34 g/cm³^[1][2]
Solid

Melting point: 2076 °C^[1]; 2077 °C^[2]

Boiling point: 3864 °C^[1]; 4000 °C^[2]

Constituents

Constituent atoms

Atom	Name	Oxidation state	Number
B	Boron	0	1

Ratio of atoms

Atom	Atomic weight	Number	Atomic ratio	Weight ratio
B	10.81	1	100.00%	100.00%

Thermodynamic properties

Phase transition properties

Item

Value

Enthalpy of fusion: 50.2 kJ · mol⁻¹^[1][2]
at 2076°C

Enthalpy of vaporization: 480 kJ · mol⁻¹^[1][2]
at 3864°C

Enthalpy of vaporization at 25°C: 552 kJ · mol⁻¹^[1]

Enthalpy of other transition: –

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	0^[3]	0^[3]	5.86^[3]	11.09^[3]
Amorphous x denotes undetermined zero point entropy	3.8^[3]	–	6.53+x^[3]	11.97^[3]
Gas	562.7^[3]	518.8^[3]	153.45^[3]	20.799^[3]

Solubility

Qualitative solubility

Reactive

Miscible

Very soluble

Soluble

Slightly soluble

Very slightly soluble

Insoluble: H₂O^[1]Water

Hazards

GHS label^[4]

Item

Value

Hazard pictograms: GHS07: Exclamation mark

Signal word: Warning

Hazard statements: H302: Harmful if swallowed

Physical hazards^[4]

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	Classification not possible
Self reactive substances and mixtures	Not applicable
Pyrophoric liquids	Not applicable
Pyrophoric solids	Classification not possible
Self heating substances and mixtures	Classification not possible
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^[4]

Classification	Category	Label	Hazard statement
Acute oral toxicity	Category 4	Warning	H302: Harmful if swallowed
Acute dermal toxicity	Classification not possible
Acute inhalation toxicity by gas	Not applicable
Acute inhalation toxicity by vapor	Classification not possible
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	Classification not possible
Specific target organ toxicity repeated exposure	Classification not possible
Aspiration hazard	Classification not possible

Environmental hazards^[4]

Classification	Category	Label	Hazard statement
Hazardous to the aquatic environment short term	Classification not possible
Hazardous to the aquatic environment long term	Classification not possible
Hazardous to the ozone layer	No data

Preparations

Reaction of reducing nonmetal and oxide

The reaction of reducing nonmetal and oxide can yield boron.

Reaction of hydrogen and diboron trioxide ◆ Δ_rG 482.26 kJ/mol K 0.32 × 10⁻⁸⁴ pK 84.49: 3H₂Hydrogen + B₂O₃Diboron trioxide
🔥
⟶
2BBoron + 3H₂OWater

Reaction of carbon and diboron trioxide ◆ Δ_rG 1204.22 kJ/mol K 0.11 × 10⁻²¹⁰ pK 210.97: 3CCarbon + 2B₂O₃Diboron trioxide
🔥
⟶
4BBoron + 3CO₂↑Carbon dioxide

Reaction of carbon and diboron trioxide ◆ Δ_rG 782.15 kJ/mol K 0.94 × 10⁻¹³⁷ pK 137.03: 3CCarbon + B₂O₃Diboron trioxide
🔥
⟶
2BBoron + 3CO↑Carbon monoxide

Electrolysis

Electrolysis of liquid can yield boron.

Electrolysis of boron trifluoride ◆ Δ_rG 2240.66 kJ/mol K 0.28 × 10⁻³⁹² pK 392.55: 2BF₃Boron trifluoride
⚡
⟶
2BBoron + 3F₂Fluorine

Electrolysis of boron tribromide ◆ Δ_rG 477.0 kJ/mol K 0.27 × 10⁻⁸³ pK 83.57: 2BBr₃Boron tribromide
⚡
⟶
2BBoron + 3Br₂Bromine

Decomposition

Decomposition of thermally decomposable substance can yield boron.

Decomposition of diborane(6) ◆ Δ_rG −86.7 kJ/mol K 1.55 × 10¹⁵ pK −15.19: B₂H₆Diborane(6)
🔥
⟶
2BBoron + 3H₂Hydrogen

Decomposition of ammonium tetraborate: (NH₄)₂B₄O₇Ammonium tetraborate
🔥
⟶
2HNO₂Nitrous acid + 4BBoron + 3H₂OWater

Decomposition of ammonium tetraborate: (NH₄)₂B₄O₇Ammonium tetraborate
🔥
⟶
N₂O₃↑Dinitrogen trioxide + 4BBoron + 4H₂OWater

Decomposition of boric acid ◆ Δ_rG 1535.41 kJ/mol K 0.10 × 10⁻²⁶⁸ pK 268.99: 2H₃BO₃Boric acid
🔥
⟶
2BBoron + 3H₂O₂Hydrogen peroxide

Decomposition of boric acid ◆ Δ_rG 1937.50 kJ/mol K 0.37 × 10⁻³³⁹ pK 339.44: 2H₃BO₃Boric acid
🔥
⟶
2BBoron + 3O₂↑Oxygen + 3H₂↑Hydrogen

Chemical reactions

Reaction with nonmetal

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

Reaction of hydrogen and boron ◆ Δ_rG 86.7 kJ/mol K 0.65 × 10⁻¹⁵ pK 15.19: 3H₂Hydrogen + 2BBoron
🔥
⟶
B₂H₆Diborane(6)

Reaction of boron and oxygen ◆ Δ_rG −2387.30 kJ/mol K 1.73 × 10⁴¹⁸ pK −418.24: 4BBoron + 3O₂Oxygen
⟶
2B₂O₃Diboron trioxide

Reaction of boron and fluorine ◆ Δ_rG −2240.66 kJ/mol K 3.52 × 10³⁹² pK −392.55: 2BBoron + 3F₂Fluorine
⟶
2BF₃Boron trifluoride

Reaction of boron and chlorine ◆ Δ_rG −777.44 kJ/mol K 1.59 × 10¹³⁶ pK −136.20: 2BBoron + 3Cl₂Chlorine
⟶
2BCl₃Boron trichloride

Reaction of boron and bromine ◆ Δ_rG −477.0 kJ/mol K 3.69 × 10⁸³ pK −83.57: 2BBoron + 3Br₂Bromine
⟶
2BBr₃Boron tribromide

Reaction with water

The reaction of boron and water yields boric acid and diborane(6).

Reaction of boron and water ◆ Δ_rG −428.0 kJ/mol K 9.60 × 10⁷⁴ pK −74.98: 4BBoron + 6H₂OWater
⟶
2H₃BO₃Boric acid + B₂H₆↑Diborane(6)

Reaction with hydroxide base

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

Reaction of boron and calcium hydroxide ◆ Δ_rG −251.8 kJ/mol K 1.30 × 10⁴⁴ pK −44.11: 4BBoron + 4Ca(OH)₂Calcium hydroxide
⟶
CaB₄O₇Calcium tetraborate + 3CaH₂Calcium hydride + H₂OWater

Reaction of boron and sodium hydroxide ◆ Δ_rG −497.9 kJ/mol K 1.69 × 10⁸⁷ pK −87.23: 4BBoron + 8NaOHSodium hydroxide
⟶
Na₂B₄O₇Sodium tetraborate + 6NaHSodium hydride + H₂OWater

Reaction of boron and sodium hydroxide ◆ Δ_rG −246.0 kJ/mol K 1.25 × 10⁴³ pK −43.10: 8BBoron + 12NaOHSodium hydroxide
⟶
Na₂B₄O₇Sodium tetraborate + 2B₂H₆↑Diborane(6) + 5Na₂OSodium oxide

Reaction of boron and magnesium hydroxide: 8BBoron + 6Mg(OH)₂Magnesium hydroxide
⟶
MgB₄O₇Magnesium tetraborate + 2B₂H₆↑Diborane(6) + 5MgOMagnesium oxide

Reaction of boron and potassium hydroxide: 4BBoron + 8KOHPotassium hydroxide
⟶
K₂B₄O₇Potassium tetraborate + 6KHPotassium hydride + H₂OWater

Reaction with base and water

The reaction of boron, base, and water yields a variety of products.

Reaction of boron, sodium hydroxide, and water ◆ Δ_rG −978.0 kJ/mol K 2.18 × 10¹⁷¹ pK −171.34: 8BBoron + 2NaOHSodium hydroxide + 5H₂OWater
⟶
Na₂B₄O₇Sodium tetraborate + 2B₂H₆↑Diborane(6)

Reaction of boron, magnesium hydroxide, and water: 8BBoron + Mg(OH)₂Magnesium hydroxide + 5H₂OWater
⟶
MgB₄O₇Magnesium tetraborate + 2B₂H₆↑Diborane(6)

Reaction of boron, potassium hydroxide, and water: 8BBoron + 2KOHPotassium hydroxide + 5H₂OWater
⟶
K₂B₄O₇Potassium tetraborate + 2B₂H₆↑Diborane(6)

Reaction of boron, calcium hydroxide, and water ◆ Δ_rG −909.5 kJ/mol K 2.18 × 10¹⁵⁹ pK −159.34: 8BBoron + Ca(OH)₂Calcium hydroxide + 5H₂OWater
⟶
CaB₄O₇Calcium tetraborate + 2B₂H₆↑Diborane(6)

Reaction of boron, lithium hydroxide, and water: 8BBoron + 2LiOHLithium hydroxide + 5H₂OWater
⟶
Li₂B₄O₇Lithium tetraborate + 2B₂H₆↑Diborane(6)

Reaction with oxidizing species

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

Reaction of boron and nitric acid ◆ Δ_rG −481.07 kJ/mol K 1.90 × 10⁸⁴ pK −84.28: BBoron + 3HNO₃Nitric acid
⟶
H₃BO₃Boric acid + 3NO₂↑Nitrogen dioxide

Reaction of boron and nitric acid ◆ Δ_rG −1011.7 kJ/mol K 1.75 × 10¹⁷⁷ pK −177.24: 2BBoron + 3HNO₃Nitric acid
⟶
B₂O₃Diboron trioxide + 3HNO₂Nitrous acid

Reaction with reducible species

The reaction of boron and manganese(IV) oxide yields diboron trioxide and manganese.

Reaction of boron and manganese(IV) oxide ◆ Δ_rG −991.88 kJ/mol K 5.89 × 10¹⁷³ pK −173.77: 4BBoron + 3MnO₂Manganese(IV) oxide
⟶
2B₂O₃Diboron trioxide + 3MnManganese

Reaction with reducing species

The reaction of hydrogen sulfide and boron yields sulfur and diborane(6).

Reaction of hydrogen sulfide and boron ◆ Δ_rG 187.4 kJ/mol K 0.15 × 10⁻³² pK 32.83: 3H₂SHydrogen sulfide + 2BBoron
🔥
⟶
3SSulfur + B₂H₆Diborane(6)

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, 2.34 g/cm³ - p.35
- ^ Melting point, 2076 °C - p.35
- ^ Boiling point, 3864 °C - p.35
- ^ Enthalpy of fusion, 50.2 kJ · mol⁻¹ - p.297
- ^ Enthalpy of vaporization, 480 kJ · mol⁻¹ - p.297
- ^ Enthalpy of vaporization at 25°C, 552 kJ · mol⁻¹ - p.297
- ^ Qualitative solubility, Insoluble in water - p.35
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, 2.34 g/cm³ - p.4-43
- ^ Melting point, 2077 °C - p.4-43
- ^ Boiling point, 4000 °C - p.4-43
- ^ Enthalpy of fusion, 50.2 kJ · mol⁻¹ - p.6-154
- ^ Enthalpy of vaporization, 480 kJ · mol⁻¹ - p.6-138
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
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	482.26 kJ/mol
K	0.32 × 10⁻⁸⁴
pK	84.49

Δ_rG	1204.22 kJ/mol
K	0.11 × 10⁻²¹⁰
pK	210.97

Δ_rG	782.15 kJ/mol
K	0.94 × 10⁻¹³⁷
pK	137.03

Δ_rG	2240.66 kJ/mol
K	0.28 × 10⁻³⁹²
pK	392.55

Boron

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

Hazards

GHS label[4]

Physical hazards[4]

Health hazards[4]

Environmental hazards[4]

Preparations

Reaction of reducing nonmetal and oxide

Electrolysis

Decomposition

Chemical reactions

Reaction with nonmetal

Reaction with water

Reaction with hydroxide base

Reaction with base and water

Reaction with oxidizing species

Reaction with reducible species

Reaction with reducing species

References

List of references

Related substances

Elementary substances of group 13 element

Boron compounds

Related categories

Classification by constituent

Type of substance

State of substance

Property of substance

Solubility of substance

Color of substance

Odor of substance

GHS label^[4]

Physical hazards^[4]

Health hazards^[4]

Environmental hazards^[4]