Pilgaard Solutions

Boron


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Other names/abbreviations: B



Element no: 5
Element group: 13 (IUPAC)
III B (American labelling)
III B (European labelling)
Element type: Nonmetals
CAS-Number: 7440-42-8
EINECS-Number: 231-151-2



Chemical properties

Reaction of boron with air
Boron does not react with air at room temperature. At higher temperatures, boron reacts with oxygen, forming boron(III)oxide, B2O3.

4 B (s) + 3 O2 (g) 2 B2O3 (s)


Reaction of boron with halogens
Boron reacts with the halogens fluorine, chlorine and bromine, forming the respective boron(III)trihalides.

2 B (s) + 3 F2 (g) 2 BF3 (g)
2 B (s) + 3 Cl2 (g) 2 BCl3 (l)
2 B (s) + 3 Br2 (g) 2 BF3 (l)


Reaction of boron with water
Boron does not react with water under normal conditions.


Solubility
Water: Insoluble (20°C) [5]


Quantitative analysis

Method 4500-B D Inductively Coupled Plasma Method [1]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.05 mg/L
Method limit of detection in soil = 1.00 mg/kg


Safety

Symbol: Xn
R-phrases: 22
S-phrases: -


Physical properties

Appearance

Physical state @ 20°C: Solid [5]
Color: Dark brown [5]
Odor: Odourless [5]


Bulk properties

Molecular weight (g/mol): 10.811(7) [2]
Melting point (°C): 2092 [2]
Boiling point (°C): 4002 [2]
Ignition temperature (°C): 700 [5]
Density (g/cm3): 1.73 (15 °C) [5]
2.35 [2]
Molar volume (cm3): 11.42
Hardness:
Mineral hardness:
11 [2]


Thermodynamic properties

ΔfH°gas (kJ/mol): 560 (Monoatomic) [2]
830.5 (B2) [4]
ΔfH°solid (kJ/mol): 0.0 (Rhombic) [4]
ΔH°fusion (kJ/mol): 50.2 [2,4]
ΔH°vaporization (kJ/mol): 480 [2]


S°gas (J/K·mol): 153.4 (Rhombic) [4]
201.9 (B2) [4]
S°solid (J/K·mol): 5.9 (Rhombic) [4]


ΔfG°gas (kJ/mol): 521.0 (Rhombic) [4]
774.0 (B2) [4]


Cp (gas) (J/K·mol): 20.8 (Rhombic, 25 °C) [4]
30.5 (B2) [4]
Cp (solid) (J/K·mol): 11.087 (25 °C) [4]


Crystal structure

Crystal type: Tetragonal [3]


Electronic properties

Electron configuration: 1s2-2s2-2p1
Ionic radius (Å): B(III): 0.27 [2]


Conductivity

e°(V): B(III)/B: -0.890 [2, a]
Electrical resisitvity (μΩ·cm): 6.7·1011 [2]


Occurrence, isolation & synthesis

Boron does not occur naturally in its elemental form but occurs boric acid B(OH)3 or H3BO3. In volcanic regions boron also occurs as the minerals borax, Na2B4O7 · 10 H2O, kernite, Na2B4O7 · 4 H2O, and colemanite Ca2B6O11 · 5 H2O [6].


Isolation
Boron can be made by reduction of the oxide B2O3 using magnesium [6].

B2O3 (s) + 3 Mg (s) 2 B (s) + 3 MgO (s) The MgO is removed by dissolving it in hydrochloric acid.


Boron can also be made by passing a mixture of boron trichloride and hydrogen through and electric arc or over a hot tungsten filament (1500 °C) [6]

2 BCl3 (g) + 3 H2 (g) 2 B (s) + 6 HCl (g)


History

Discovery
Boron compounds have been known for thousands of years, but the element was not isolated until 1808 by Sir Humphry Davy, Joseph-Louis Gay-Lussac and Louis Jaques Thénard [4].

Origin of name
From Arabic "buraq" and Persian "burah" [4].


References

1: Standard Methods for the Analysis of Water and Wastewater, APHA, 1992, 18th edition

2: Greenwood,N.N., Earnshaw,A. Chemistry of the elements
2nd edition (1997) Edited by Greenwood,N.N., Earnshaw,A. pp. 1-1340, Butterworth-Heinemann. Oxford. Great Britain

3: Buch,A. Pure Metals Properties. A Scientific-Technical Handbook
1st edition (1999) Edited by Buch,A. pp. 1-306, ASM International and Freund Publishing House Ltd. Ohio. USA

4: CRC Handbook of Chemistry and Physics
75th edition (1994) Edited by Lide,D.R. , CRC Press Inc. Boca Raton, USA

5: Merck. ChemDAT The Merck Chemical Database Ver. 1.1.5

6: General chemistry
7th edition (1984) Edited by Holtzclaw, Jr.,H.F., Robinson,W.R. & Nebergall,W.H. pp. 1-932. D.C. Heath and Company. Lexington







© Michael Pilgaard
Created: May 5, 2008
Last update: May 2, 2008