Boron

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Boron Quick Reference

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Notes

Symbol

B

Atomic Number

5

Atomic Weight

Rounded

10.81

for regular calculations

Standard

10.806 to 10.821

for precise calculations

Oxidation States

3

more common

2

less common

1

less common

Pauling Electronegativity

2.04

Electron Configuration

Orbital Occupancy

[He] 2s2 2p1

[He] represents the closed-shell electron configuration of helium

Orbital Filling Order

[He] 2s2 2p1

[He] represents the closed-shell electron configuration of helium

Term Symbol

2P1/2

see expanded configuration ...

Ionization Energies

I   (1)

  8.29802 eV

II  (2)

 25.1548 eV 

III (3)

 37.93064 eV

IV  (4)

259.37521 eV

V   (5)

340.22580 eV

Electron Affinity

0.279723 ± 0.000025 eV

 2256.12 ± 0.20 cm-1  

Density

liquid, 2348.15 K

2.160 g/ml 

solid, 25 °C

2.340 g/cm3

Molar Volume

solid, 298 K, 1 atm

4.39 cm3/mol

Melting Point

1 bar

2350 ± 50 K

Boiling Point

1 atm

4273.15 K

Thermal Conductivity

solid

300 K, polycrystalline

27.0 W/(m K)

298.2 K, polycrystalline

27.4 W/(m K)

Pyykkö Covalent Radius

single bond

85 pm

double bond

78 pm

triple bond

73 pm

Atomic Radius

80 pm

Enthalpy of Fusion

1 atm

22.2 kJ/mol

Enthalpy of Vaporization

1 atm

538.9 kJ/mol

Quantity

Boron Atomic Structure

Notes

Ionization Energies

I   (1)

  8.29802 eV

II  (2)

 25.1548 eV 

III (3)

 37.93064 eV

IV  (4)

259.37521 eV

V   (5)

340.22580 eV

Electron Affinity

0.279723 ± 0.000025 eV

 2256.12 ± 0.20 cm-1  

Electron Binding Energies

(1s)

188 eV

Electron Configuration

Orbital Occupancy

[He] 2s2 2p1

[He] represents the closed-shell electron configuration of helium

Orbital Filling Order

[He] 2s2 2p1

[He] represents the closed-shell electron configuration of helium

Term Symbol

2P1/2

see expanded configuration ...

Clementi-Raimondi Effective Nuclear Charge

1s

Orbital Exponent

4.6795

ζ

Principle Quantum Number

1

n

Effective Nuclear Charge

4.6795

Zeff = ζ × n

2s

Orbital Exponent

1.2881

ζ

Principle Quantum Number

2

n

Effective Nuclear Charge

2.5762

Zeff = ζ × n

2p

Orbital Exponent

1.2107

ζ

Principle Quantum Number

2

n

Effective Nuclear Charge

2.4214

Zeff = ζ × n

Screening Percentage

48.0%

Fluorescence Yields

ωK

0.0014

Quantity

Boron Physical Properties

Notes

Density

liquid, 2348.15 K

2.160 g/ml 

solid, 25 °C

2.340 g/cm3

Molar Mass

Rounded

10.81 g/mol

for regular calculations

Standard

10.806 g/mol to 10.821 g/mol

for precise calculations

Molar Volume

solid, 298 K, 1 atm

4.39 cm3/mol

Physical Form

black rhombohedral crystals

Speed of Sound

solid

16200 m/s

calculated value

Young's Modulus

β-rhombohedral boron

440 GPa

Dielectric Constant

β-rhombohedral boron

parallel to crystal axis, low frequency limit

10.24

perpendicular to crystal axis, low frequency limit

11.55

parallel to crystal axis, high frequency limit

 8.41

perpendicular to crystal axis, high frequency limit

 9.12

Photoelectric Work Function

4.5 eV

Superconducting Transition Temperature

250 GPa

11.2 K

maximum temperature

175 GPa

 6 K  

Mineralogical Hardness

9.3

Vickers Hardness

293 K

49000 MN/m2

Isothermal Bulk Modulus

300 K

178 GPa

Isothermal Compressibility

300 K

0.00562 GPa-1

Gram Atomic Volume

5 cm3

Quantity

Boron Atomic Interaction

Notes

Oxidation States

3

more common

2

less common

1

less common

Pauling Electronegativity

2.04

Mulliken-Jaffe Electronegativity

hybridsp2

2.04

hybridsp3

1.90

Sanderson Electronegativity

oxidation state: 3

2.275

oxidation state: 2

2.19

oxidation state: 1

1.53

Allred-Rochow Electronegativity

2.01

Configuration Energy

electron volt units

12.13 eV

Pauling units

 2.051  

Allen Electronegativity

2.051

Allred Electronegativity

oxidation state: 3

2.04

Boyd-Edgecombe Electronegativity

1.90

Ghosh-Gupta Electronegativity

4.9686 eV

Nagle Electronegativity

2.02

Pearson Absolute Electronegativity

4.29 eV

Smith Electronegativity

oxidation state: 3

1.9

Chemical Hardness

4.01 eV

Cohesive Energy

per mole

561 kJ/mol    

per atom

  5.81 eV/atom

Quantity

Boron Thermodynamics

Notes

Melting Point

1 bar

2350 ± 50 K

Boiling Point

1 atm

4273.15 K

Thermal Conductivity

solid

300 K, polycrystalline

27.0 W/(m K)

298.2 K, polycrystalline

27.4 W/(m K)

Critical Point

3284 K

Vapor Pressure

3799 °C

100 kPa

3272 °C

10 kPa

2868 °C

1 kPa

2549 °C

100 Pa

2289 °C

10 Pa

2075 °C

1 Pa

Enthalpy of Fusion

1 atm

22.2 kJ/mol

Enthalpy of Vaporization

1 atm

538.9 kJ/mol

Isobaric Molar Heat Capacity

298.15 K, 1 bar

11.087 J/(mol K)

Isobaric Specific Heat Capacity

298.15 K, 1 bar

1.026 J/(g K)

Debye Temperature

Low Temperature Limit ( 0 K )

1480 K

Room Temperature ( 298 K )

1362 K

Quantity

Boron Identification

Notes

CAS Number

7440-42-8

Quantity

Boron Atomic Size

Notes

Atomic Radius

80 pm

Orbital Radius

77.6 pm

Pyykkö Covalent Radius

single bond

85 pm

double bond

78 pm

triple bond

73 pm

Cordero Covalent Radius

84 pm

Shannon-Prewitt Crystal Radius

ion charge: +3

coordination number: 3

15 pm

coordination number: 4

25 pm

coordination number: 6

41 pm

Shannon-Prewitt Effective Ionic Radius

ion charge: +3

coordination number: 3

 1 pm

coordination number: 4

11 pm

coordination number: 6

27 pm

Pauling Univalent Radius

ion charge: +1

35 pm

Batsanov Crystallographic Van Der Waals Radius

1.8×102 pm

Batsanov Equilibrium Van Der Waals Radius

205 pm

Slater Atomic-Ionic Radius

85 pm

Quantity

Boron Crystal Structure

Notes

Allotropes

allotrope

α-rhombohedral boron

alternate name

Rhombohedral-12 Boron

symbol

α-R12

allotrope

β-rhombohedral boron

alternate name

Rhombohedral-105 Boron

symbol

β-R105

allotrope

β-tetragonal boron

alternate name

Tetragonal-192 Boron

symbol

β-T192

Atomic Concentration

300 K, 1 atm

13.0×1022 cm-3

Quantity

Boron History

Notes

Discovery

shared discovery

date of discovery

1808

discoverer

Louis-Joseph Gay-Lussac

birth

December 6, 1778

death

May 9, 1850

discoverer

Louis-Jacques Thenard

birth

May 4, 1777

death

June 21, 1857

location of discovery

Paris, France

shared discovery

date of discovery

1808

discoverer

Humphry Davy

birth

December 17, 1778

death

May 29, 1829

location of discovery

London, England

Origin of Element Name

origin

bauraq

origin description

mineral—Arabic for borax

Origin of Element Symbol

symbol: B

origin

boron

origin description

element name

U.S. Towns Named After Elements

Boron, California

Formerly Used or Proposed Element Names and Symbols

name

bore

no matching symbol specified

name

boracium

no matching symbol specified

Quantity

Boron Abundances

Notes

Earth's Crust

1.0×101 ppm

Earth's Mantle

0.26 ppm

primitive mantle

Bulk Earth

0.2 ppm

Ocean Water

4.5 ppm

Metalliferous Ocean Sediment

Basal

123 ppm

Ridge

500 ppm

River Water

0.01 ppm

U.S. Coal

49 ppm

Human Body

18 mg

based on a 70 kg "reference man"

Human Bone

1.1 ppm to 3.3 ppm

Human Hair

5 ppm

Human Kidney

0.9 ppm to 2.6 ppm

Human Liver

0.4 ppm to 2.3 ppm

Human Muscle

0.33 ppm to 1 ppm

Human Nail

33 ppm

Bacteria

5.5 ppm

Ferns

77 ppm

Fungi

16 ppm

Solar System

21.2

number of atoms for every 106 atoms of silicon

Sun

2.70 ± 0.16

base 10 log of the number of atoms for every 1012 atoms of hydrogen

Meteorites

2.88 ± 0.04

base 10 log of the number of atoms for every 1012 atoms of hydrogen

Quantity

Boron Nomenclature

Notes

Element Names in Other Languages

French

bore

German

Bor

Italian

boro

Spanish

boro

Portuguese

boro

Anions or Anionic Substituent Groups

boride (general)

B-, boride(1-)

B3-, boride(3-)

Cations or Cationic Substituent Groups

boron (general)

B+, boron(1+)

B3+, boron(3+)

Ligands

borido (general)

B-, borido(1-)

B3-, borido(3-)

Heteroatomic Anion

borate

'a' Term—Substitutive Nomenclature

bora

'y' Term—Chains and Rings Nomenclature

bory

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