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Iron Quick Reference

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Notes

Symbol

Fe

Atomic Number

26

Atomic Weight

Rounded

55.85

for regular calculations

Standard

55.845 ± 0.002

for precise calculations

Oxidation States

 6

less common

 5

less common

 4

less common

 3

more common

 2

more common

 1

less common

 0

less common

-1

less common

-2

less common

Pauling Electronegativity

oxidation state: 3

1.96

oxidation state: 2

1.83

Electron Configuration

Orbital Occupancy

[Ar] 3d6 4s2

[Ar] represents the closed-shell electron configuration of argon

Orbital Filling Order

[Ar] 4s2 3d6

[Ar] represents the closed-shell electron configuration of argon

Term Symbol

5D4

see expanded configuration ...

Ionization Energies

I   (1)

 7.9024 eV       

II  (2)

16.1877 eV       

III (3)

30.652 ± 0.010 eV

IV  (4)

54.8 ± 0.1 eV    

see all 26 energies ...

Electron Affinity

0.151 ± 0.003 eV

 1220 ± 25 cm-1 

Density

liquid

2400 K

6.490 g/ml 

2300 K

6.582 g/ml 

2200 K

6.675 g/ml 

2100 K

6.767 g/ml 

2000 K

6.860 g/ml 

1900 K

6.953 g/ml 

solid, 25 °C

7.870 g/cm3

see all 15 densities ...

Molar Volume

solid, 298 K, 1 atm

7.09 cm3/mol

Melting Point

1 atm

1811 K

ITS-90 second-quality, secondary reference point (freezing point)

Boiling Point

1 atm

3133.35 K

Thermal Conductivity

solid

400 K

69.5 W/(m K)

300 K

80.2 W/(m K)

298.2 K

80.4 W/(m K)

273.2 K

83.5 W/(m K)

200 K

94.0 W/(m K)

see all 52 conductivities ...

Pyykkö Covalent Radius

single bond

116 pm

double bond

109 pm

triple bond

102 pm

Atomic Radius

126 pm

Enthalpy of Fusion

1 atm

14.9 kJ/mol

Enthalpy of Vaporization

1 atm

351 kJ/mol

Quantity

Iron Atomic Structure

Notes

Ionization Energies

I   (1)

 7.9024 eV       

II  (2)

16.1877 eV       

III (3)

30.652 ± 0.010 eV

IV  (4)

54.8 ± 0.1 eV    

see all 26 energies ...

Electron Affinity

0.151 ± 0.003 eV

 1220 ± 25 cm-1 

Electron Binding Energies

K    (1s)

7112 eV  

LI   (2s)

 844.6 eV

LII  (2p1/2)

 719.9 eV

LIII (2p3/2)

 706.8 eV

see all 7 energies ...

Electron Configuration

Orbital Occupancy

[Ar] 3d6 4s2

[Ar] represents the closed-shell electron configuration of argon

Orbital Filling Order

[Ar] 4s2 3d6

[Ar] represents the closed-shell electron configuration of argon

Term Symbol

5D4

see expanded configuration ...

Clementi-Raimondi Effective Nuclear Charge

1s

Orbital Exponent

25.3810

ζ

Principle Quantum Number

1

n

Effective Nuclear Charge

25.3810

Zeff = ζ × n

2s

Orbital Exponent

 9.2995

ζ

Principle Quantum Number

2

n

Effective Nuclear Charge

18.599 

Zeff = ζ × n

see all 7 effective nuclear charges ...

Screening Percentage

77.5%

Fluorescence Yields

ωK

0.355 

ωL1

0.0010

ωL2

0.0063

ωL3

0.0063

Coster-Kronig Yields

F12

0.30

F13

0.57

Quantity

Iron Physical Properties

Notes

Density

liquid

2400 K

6.490 g/ml 

2300 K

6.582 g/ml 

2200 K

6.675 g/ml 

2100 K

6.767 g/ml 

2000 K

6.860 g/ml 

1900 K

6.953 g/ml 

solid, 25 °C

7.870 g/cm3

see all 15 densities ...

Molar Mass

Rounded

55.85 g/mol

for regular calculations

Standard

55.845 ± 0.002 g/mol

for precise calculations

Molar Volume

solid, 298 K, 1 atm

7.09 cm3/mol

Physical Form

silvery-white or gray metal

Linear Thermal Expansion Coefficient

25 °C

11.8×10-6 K-1

293 K

11.8×10-6 K-1

Speed of Sound

solid

room temperature, cast, longitudinal wave

4994 m/s

room temperature, cast, shear wave

2809 m/s

room temperature, cast, extensional wave

4480 m/s

473 K

4720 m/s

373 K

5300 m/s

20 °C

longitudinal wave

5957 m/s

shear wave

3224 m/s

see all 15 speeds of sound ...

Young's Modulus

208.2 GPa

Poisson's Ratio

0.291

Electrical Resistivity

α-Iron, solid

200 K

5.20×10-8 Ohm m

273 K

8.57×10-8 Ohm m

293 K

9.61×10-8 Ohm m

300 K

9.98×10-8 Ohm m

400 K

16.1×10-8 Ohm m

see all 35 resistivities ...

Contact Potential

4.40 eV

Photoelectric Work Function

4.33 eV

Thermionic Work Function

4.25 eV

Superconducting Transition Temperature

20 GPa, crystallographic hcp phase, non-magnetic

2 K

maximum temperature

Mineralogical Hardness

4.0

Vickers Hardness

carbonyl

293 K

608 MN/m2

473 K

598 MN/m2

see all 10 hardnesses ...

Reflectivity

surface polished

0.5 μm

55%

0.6 μm

57%

0.7 μm

59%

see all 8 reflectivities ...

Isothermal Bulk Modulus

300 K

168.3 GPa

Isothermal Compressibility

300 K

0.00594 GPa-1

Gram Atomic Volume

7 cm3

Quantity

Iron Atomic Interaction

Notes

Oxidation States

 6

less common

 5

less common

 4

less common

 3

more common

 2

more common

 1

less common

 0

less common

-1

less common

-2

less common

Pauling Electronegativity

oxidation state: 3

1.96

oxidation state: 2

1.83

Sanderson Electronegativity

oxidation state: 3

2.20

oxidation state: 2

1.64

Allred-Rochow Electronegativity

oxidation state: 2

1.64

Configuration Energy

electron volt units

10.64 eV

Pauling units

 1.80   

Allred Electronegativity

oxidation state: 2

1.83

Ghosh-Gupta Electronegativity

3.5836 eV

Nagle Electronegativity

1.40

Pearson Absolute Electronegativity

4.06 eV

Smith Electronegativity

oxidation state: 3

1.9

oxidation state: 2

1.75

Chemical Hardness

3.81 eV

Cohesive Energy

per mole

413 kJ/mol    

per atom

  4.28 eV/atom

Quantity

Iron Thermodynamics

Notes

Melting Point

1 atm

1811 K

ITS-90 second-quality, secondary reference point (freezing point)

Boiling Point

1 atm

3133.35 K

Thermal Conductivity

solid

400 K

69.5 W/(m K)

300 K

80.2 W/(m K)

298.2 K

80.4 W/(m K)

273.2 K

83.5 W/(m K)

200 K

94.0 W/(m K)

see all 52 conductivities ...

Triple Point

α-γ-ε triple point

temperature

678 K

pressure

8.2 ± 0.1 GPa

γ-δ-liquid triple point

temperature

1718 °C

pressure

5.2 GPa

Critical Point

temperature

9250 K

The temperature value has an uncertainty of ±12%.

pressure

8750 bar

The pressure value has an uncertainty of ±14%.

Vapor Pressure

2859 °C

100 kPa

2406 °C

10 kPa

2073 °C

1 kPa

1818 °C

100 Pa

1617 °C

10 Pa

1455 °C

1 Pa

Curie Point

1044 ± 2 K

Enthalpy of Fusion

1 atm

14.9 kJ/mol

Enthalpy of Vaporization

1 atm

351 kJ/mol

Isobaric Molar Heat Capacity

298.15 K, 1 bar

25.10 J/(mol K)

Isobaric Specific Heat Capacity

298.15 K, 1 bar

0.449 J/(g K)

Electronic Heat Capacity Coefficient

4.90 mJ/(mol K2)

Debye Temperature

Low Temperature Limit ( 0 K )

477 K

Room Temperature ( 298 K )

373 K

α-Iron, Low Temperature Limit ( 0 K )

477 K

Quantity

Iron Identification

Notes

CAS Number

7439-89-6

Quantity

Iron Atomic Size

Notes

Atomic Radius

126 pm

Orbital Radius

122.7 pm

Pyykkö Covalent Radius

single bond

116 pm

double bond

109 pm

triple bond

102 pm

Cordero Covalent Radius

low spin

132 pm

high spin

152 pm

Shannon-Prewitt Crystal Radius

ion charge: +2

coordination number: 4, high spin

 77 pm  

square planer

 78 pm  

coordination number: 6

low spin

 75 pm  

high spin

 92.0 pm

coordination number: 8, high spin

106 pm  

ion charge: +3

coordination number: 4, high spin

 63 pm  

coordination number: 5

 72 pm  

coordination number: 6

low spin

 69 pm  

high spin

 78.5 pm

coordination number: 8, high spin

 92 pm  

ion charge: +4, coordination number: 6

 72.5 pm

ion charge: +6, coordination number: 4

 39 pm  

Shannon-Prewitt Effective Ionic Radius

ion charge: +2

coordination number: 4, high spin

63 pm  

square planer

64 pm  

coordination number: 6

low spin

61 pm  

high spin

78.0 pm

coordination number: 8, high spin

92 pm  

ion charge: +3

coordination number: 4, high spin

49 pm  

coordination number: 5

58 pm  

coordination number: 6

low spin

55 pm  

high spin

64.5 pm

coordination number: 8, high spin

78 pm  

ion charge: +4, coordination number: 6

58.5 pm

ion charge: +6, coordination number: 4

25 pm  

Pauling Empirical Crystal Radius

ion charge: +3

64 pm

ion charge: +2

76 pm

Batsanov Crystallographic Van Der Waals Radius

205 pm

Batsanov Equilibrium Van Der Waals Radius

227 pm

Slater Atomic-Ionic Radius

140 pm

Quantity

Iron Crystal Structure

Notes

Allotropes

allotrope

α-Iron

symbol

αFe

allotrope

γ-Iron

symbol

γFe

allotrope

δ-Iron

symbol

δFe

allotrope

ε-Iron

symbol

εFe

Nearest Neighbor Distance

300 K, 1 atm

248 pm

Atomic Concentration

300 K, 1 atm

8.50×1022 cm-3

Quantity

Iron History

Notes

Discovery

date of discovery

circa 2500 BC

discoverer

unknown

location of discovery

unknown

Origin of Element Name

origin

iren

origin description

word—Anglo-Saxon

Origin of Element Symbol

symbol: Fe

origin

ferrum

origin description

word—Latin for iron

U.S. Towns Named After Elements

Iron, Minnesota

Quantity

Iron Abundances

Notes

Earth's Crust

5.63×104 ppm

Earth's Mantle

6.30%

primitive mantle

Earth's Core

85.5%

Bulk Earth

32.0%

Ocean Water

0.003 ppm

Metalliferous Ocean Sediment

Basal

20%

Ridge

18%

River Water

0.67 ppm

U.S. Coal

1.3 ppm

Human Body

4.2 g

based on a 70 kg "reference man"

Human Bone

3 ppm to 380 ppm

Human Hair

5 ppm to 45 ppm

Human Kidney

170 ppm to 710 ppm

Human Liver

250 ppm to 1400 ppm

Human Muscle

180 ppm

Human Nail

27 ppm to 350 ppm

Bacteria

170 ppm

Ferns

320 ppm to 700 ppm

Fungi

90 ppm to 2×103 ppm

Universe

0.00003

relative to hydrogen = 1.00000

Solar System

9.00×105

number of atoms for every 106 atoms of silicon

Sun

7.50 ± 0.05

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

Moon

Terrae

1.8 ± 0.3 %

Maria

4.4 ± 0.7 %

Average

2.3%

Meteorites

7.48 ± 0.01

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

Halley's Comet

52 ± 9 atoms

number of atoms for every 100 atoms of magnesium

Quantity

Iron Nomenclature

Notes

Element Names in Other Languages

French

fer

German

Eisen

Italian

ferro

Spanish

hierro

Portuguese

ferro

Anions or Anionic Substituent Groups

ferride

Cations or Cationic Substituent Groups

iron (general)

Fe2+, iron(2+)

Fe3+, iron(3+)

Ligands

ferrido

Heteroatomic Anion

ferrate

'a' Term—Substitutive Nomenclature

ferra

'y' Term—Chains and Rings Nomenclature

ferry

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