Fe 26

Iron (Fe)

transition-metal

Period: 4 Group: 8 Block: s

Solid

Standard Atomic Weight

Electron configuration

[Ar] 4s² 3d⁶

Melting point

1537.85 °C (1811 K)

Boiling point

2860.85 °C (3134 K)

Density

7874 kg/m³

Oxidation states

−4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7

Electronegativity (Pauling)

1.83

Ionization energy (1st)

Discovery year

N/A

Atomic radius

140 pm

Details

Name origin Anglo-Saxon: iron; symbol from Latin: ferrum (iron).

Discoverers Known to the ancients.

Iron is a first-row transition metal and one of the central elements of technology and biology. It forms strong, workable alloys, especially with carbon, and has accessible Fe²⁺ and Fe³⁺ redox chemistry. In Earth materials it is a major constituent of the core, mantle minerals, and many ores. Its magnetic behavior and ability to bind small molecules in metalloproteins give it importance beyond structural metal use.

The pure metal is very reactive chemically and rapidly corrodes, especially in moist air or at elevated temperatures. It has four allotropic forms or ferrites, known as alpha, beta, gamma, and omega, with transition points at 700, 928, and 1530C. The alpha form is magnetic, but when transformed into the beta form, the magnetism disappears although the lattice remains unchanged. The relations of these forms are peculiar. Pig iron is an alloy containing about 3 percent carbon with varying amounts of sulfur, silicon, manganese, and phosphorus.

Iron is hard, brittle, fairly fusible, and is used to produce other alloys, including steel. Wrought iron contains only a few tenths of a percent of carbon, is tough, malleable, less fusible, and usually has a "fibrous" structure.

Carbon steel is an alloy of iron with small amounts of Mn, S, P, and Si. Alloy steels are carbon steels with other additives such as nickel, chromium, vanadium, etc. Iron is a cheap, abundant, useful, and important metal.

The name derives from the Anglo-Saxon iron of unknown origin. The element has been known from prehistoric times. The symbol Fe is derived from the Latin ferrum for "firmness". It is of interest to note that 56Fe requires more energy to be formed than any other nuclide. It is, therefore, the ultimate endproduct of stellar nuclear fusion.

Archaeological evidence suggests that people have been using iron for at least 5000 years. Iron is the cheapest and one of the most abundant of all metals, comprising nearly 5.6% of the earth's crust and nearly all of the earth's core. Iron is primarily obtained from the minerals hematite (Fe2O3) and magnetite (Fe3O4). The minerals taconite, limonite (FeO(OH)·nH2O) and siderite (FeCO3) are other important sources.

Latin ferrum. Iron was used prehistorically:

▸ Iron is mentioned numerous times in the Old Testament of the Bible.

▸ A remarkable iron pillar, dating to about A.D. 400, remains standing today in Delhi, India. This solid shaft of wrought iron is about 7 1/4 m high by 40 cm in diameter. Corrosion to the pillar has been minimal although it has been exposed to the weather since its creation.

Read about Iron on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 140 pm

Covalent radius 132 pm

Van der Waals radius 194 pm

Metallic radius 117 pm

Density

Molar volume 0.0071 L/mol

Phase at STP solid

Melting point 1537.85 °C

Boiling point 2860.85 °C

Thermal conductivity 80.4 W/(m·K)

Specific heat capacity 0.449 J/(g·K)

Molar heat capacity 25.1 J/(mol·K)

Crystal structure bcc

Chemical

Electronegativity (Pauling) 1.83

Electronegativity (Allen) 1.8

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states −4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7

Valence electrons 8

Electron configuration

Electron configuration (semantic)

Thermodynamic

Critical point (temperature) 9067 °C

Heat of fusion 0.14313106 eV

Heat of vaporization 3.523864 eV

Heat of sublimation 4.306369 eV

Heat of atomization 4.306369 eV

Atomization enthalpy

Nuclear

Stable isotopes 4

Abundance

Abundance (Earth's crust) 5.630e+4 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 287 pm

Electronic Structure

Electrons per shell 2, 8, 14, 2

Identifiers

CAS number 7439-89-6

Term symbol

InChI InChI=1S/Fe

InChI Key XEEYBQQBJWHFJM-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 26

Electrons 26

Charge Neutral

Configuration Fe: 3d⁶ 4s²

[Ar] 3d⁶ 4s²

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

↑

6/10 4↑

Total electrons: 26 Unpaired: 4

Atomic model

Protons 26

Neutrons 30

Electrons 26

Mass number 56

Stability Stable

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

Emission Visible: 380–750 nm

Isotope Distribution

Mass number	Atomic mass (u)	Natural abundance	Half-life
54 Stable	53.93960899 ± 0.00000053	5.8450%	Stable
56 Stable	55.93493633 ± 0.00000049	91.7540%	Stable
57 Stable	56.93539284 ± 0.00000049	2.1190%	Stable
58 Stable	57.93327443 ± 0.00000053	0.2820%	Stable

Measured

Phase / State

Solid 25 °C (298.15 K)

Reason: 1512.8 °C below melting point (1537.85 °C)

Melting point 1537.85 °C

Boiling point 2860.85 °C

Below melting by 1512.8 °C

0 K Current temperature: 25 °C 6000 K

Phase timeline

Schematic, not to scale

Solid

Liquid

Gas

Melting

Boiling

25°C

Solid

Liquid

Gas

Current

Phase transition points

Melting point Literature

1537.85 °C

Boiling point Literature

2860.85 °C

Current phase Calculated
Solid

Transition energies

Heat of fusion Literature

0.14313106 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

3.523864 eV

Energy required to vaporize 1 mol at boiling point

Heat of sublimation Literature

4.306369 eV

Energy required to sublime 1 mol at sublimation point

Density

Reference density Literature

7874 kg/m³

At standard conditions

Current density Calculated

7874 kg/m³

At standard conditions

Advanced

Critical point Literature

9067 °C

Atomic Spectra

Showing 10 of 26 Atomic Spectra. Sorted by ion charge (ascending).

Lines Holdings ?

Ion	Charge	Total lines	Transition probabilities	Level designations
Fe I	0	10031	2542	9906
Fe II	+1	14471	7293	14471
Fe III	+2	4702	2361	4687
Fe IV	+3	258	102	102
Fe V	+4	2310	2018	2310
Fe VI	+5	159	159	159
Fe VII	+6	651	651	651
Fe VIII	+7	92	63	92
Fe IX	+8	56	14	56
Fe X	+9	98	64	98

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
Fe I	0	847
Fe II	+1	1028
Fe III	+2	596
Fe IV	+3	277
Fe V	+4	332
Fe VI	+5	94
Fe VII	+6	210
Fe VIII	+7	42
Fe IX	+8	35
Fe X	+9	65

NIST Levels Holdings →

26 Fe 55.845

Iron — Atomic Orbital Visualizer

[Ar]4s23d6

Energy levels 2 8 14 2

Oxidation states -4, -2, -1, 0, +1, +2, +3, +4, +5, +6, +7

HOMO 3d n=3 · l=2 · m=-2

Iron — Atomic Orbital Visualizer Preview

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26 Fe 55.845

Iron — Crystal Structure Visualizer

Body-Centered Cubic · Pearson cI2

Experimental

Pearson cI2

Coord. № 8

Packing 68.000%

Iron — Crystal Structure Visualizer Preview

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Ionic Radii

Showing 10 of 12 Ionic Radii.

Charge	Coordination	Spin	Radius
+2	4	high	63 pm
+2	4	high	64 pm
+2	6	low	61 pm
+2	6	high	78 pm
+2	8	high	92 pm
+3	4	high	49 pm
+3	5	N/A	57.99999999999999 pm
+3	6	low	55.00000000000001 pm
+3	6	high	64.5 pm
+3	8	high	78 pm

Compounds

55.840 u

Fe+2

55.840 u

Fe+3

55.840 u

55.935 u

54.938 u

58.935 u

56.935 u

59.934 u

Fe+3

54.938 u

51.948 u

Fe+4

55.840 u

Fe+6

55.840 u

Fe+5

55.840 u

57.933 u

53.940 u

Fe+3

58.935 u

Fe+2

56.935 u

50.957 u

Fe+2

54.938 u

Fe+2

58.935 u

Fe+3

51.948 u

Fe+2

57.933 u

Isotopes (4)

Common iron is a mixture of four isotopes. Ten other isotopes are known to exist.

Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
54 Stable	53.93960899 ± 0.00000053	5.8450% ± 0.0350%	Stable	stable
56 Stable	55.93493633 ± 0.00000049	91.7540% ± 0.0360%	Stable	stable
57 Stable	56.93539284 ± 0.00000049	2.1190% ± 0.0100%	Stable	stable
58 Stable	57.93327443 ± 0.00000053	0.2820% ± 0.0040%	Stable	stable

54 Stable

Atomic mass (u) 53.93960899 ± 0.00000053

Natural abundance 5.8450% ± 0.0350%

Half-life Stable

Decay mode

stable

56 Stable

Atomic mass (u) 55.93493633 ± 0.00000049

Natural abundance 91.7540% ± 0.0360%

Half-life Stable

Decay mode

stable

57 Stable

Atomic mass (u) 56.93539284 ± 0.00000049

Natural abundance 2.1190% ± 0.0100%

Half-life Stable

Decay mode

stable

58 Stable

Atomic mass (u) 57.93327443 ± 0.00000053

Natural abundance 0.2820% ± 0.0040%

Half-life Stable

Decay mode

stable

Spectral Lines

Showing 50 of 5034 Spectral Lines. Only spectral lines with measured intensity are shown by default.

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
387.857282 nm	1290000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
393.02964 nm	1150000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
385.637115 nm	1100000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
389.970707 nm	1070000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
526.95366 nm	1020000	Fe I	emission	3d7.(4F).4s a 5F → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
382.444329 nm	1000000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
392.291129 nm	1000000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
404.581193 nm	1000000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3F*	Measured	NIST
649.49801 nm	870000	Fe I	emission	3d6.4s2 a 3H → 3d7.(4F).4p z 5G*	Measured	NIST
406.359365 nm	830000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3F*	Measured	NIST
432.57616 nm	830000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p z 3G*	Measured	NIST
440.47498 nm	810000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p z 5G*	Measured	NIST
381.58397 nm	760000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3D*	Measured	NIST
382.588058 nm	760000	Fe I	emission	3d7.(4F).4s a 5F → 3d7.(4F).4p y 5D*	Measured	NIST
516.74879 nm	760000	Fe I	emission	3d7.(4F).4s a 3F → 3d6.(5D).4s.4p.(3P) z 3D	Measured	NIST
389.565597 nm	740000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
532.80381 nm	740000	Fe I	emission	3d7.(4F).4s a 5F → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
407.173752 nm	710000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3F*	Measured	NIST
392.025748 nm	650000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
427.17599 nm	630000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p z 3G*	Measured	NIST
430.79017 nm	630000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p z 3G*	Measured	NIST
382.78222 nm	590000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3D*	Measured	NIST
383.422219 nm	590000	Fe I	emission	3d7.(4F).4s a 5F → 3d7.(4F).4p y 5D*	Measured	NIST
388.628183 nm	550000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
640 nm	490000	Fe I	emission	3d6.(5D).4s.4p.(3P) z 5P → 3d6.(5D).4s (6D).5s e 5D	Measured	NIST
384.10475 nm	457000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3D*	Measured	NIST
522.71889 nm	437000	Fe I	emission	3d7.(4F).4s a 3F → 3d6.(5D).4s.4p.(3P) z 3D	Measured	NIST
396.925691 nm	427000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3F*	Measured	NIST
381.296424 nm	398000	Fe I	emission	3d7.(4F).4s a 5F → 3d6.(5D).4s.4p.(3P) z 3P	Measured	NIST
537.14891 nm	389000	Fe I	emission	3d7.(4F).4s a 5F → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
384.04372 nm	380000	Fe I	emission	3d7.(4F).4s a 5F → 3d7.(4F).4p y 5D*	Measured	NIST
414.386752 nm	363000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3F*	Measured	NIST
390.294512 nm	302000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3D*	Measured	NIST
639.36001 nm	302000	Fe I	emission	3d6.4s2 a 3H → 3d7.(4F).4p z 5G*	Measured	NIST
495.75961 nm	295000	Fe I	emission	3d6.(5D).4s.4p.(3P) z 7F → 3d6.(5D).4s (6D).5s e 7D	Measured	NIST
441.51221 nm	288000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p z 5G*	Measured	NIST
527.03561 nm	288000	Fe I	emission	3d7.(4F).4s a 3F → 3d6.(5D).4s.4p.(3P) z 3D	Measured	NIST
387.801779 nm	275000	Fe I	emission	3d7.(4F).4s a 5F → 3d7.(4F).4p y 5D*	Measured	NIST
642.13496 nm	257000	Fe I	emission	3d6.4s2 a 3P2 → 3d6.(5D).4s.4p.(3P) z 3P	Measured	NIST
388.704779 nm	251000	Fe I	emission	3d7.(4F).4s a 5F → 3d7.(4F).4p y 5D*	Measured	NIST
667.79848 nm	240000	Fe I	emission	3d7.(2G).4s a 3G → 3d7.(4F).4p y 3F*	Measured	NIST
387.250102 nm	234000	Fe I	emission	3d7.(4F).4s a 5F → 3d7.(4F).4p y 5D*	Measured	NIST
390.647918 nm	234000	Fe I	emission	3d6.4s2 a 5D → 3d6.(5D).4s.4p.(3P) z 5D	Measured	NIST
413.205785 nm	224000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3F*	Measured	NIST
426.04736 nm	224000	Fe I	emission	3d6.(5D).4s.4p.(3P) z 7D → 3d6.(5D).4s (6D).5s e 7D	Measured	NIST
654.62373 nm	224000	Fe I	emission	3d7.(2G).4s a 3G → 3d7.(4F).4p y 3F*	Measured	NIST
641.16477 nm	219000	Fe I	emission	3d6.(5D).4s.4p.(3P) z 5P → 3d6.(5D).4s (6D).5s e 5D	Measured	NIST
425.07864 nm	214000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p z 3G*	Measured	NIST
400.524148 nm	209000	Fe I	emission	3d7.(4F).4s a 3F → 3d7.(4F).4p y 3F*	Measured	NIST
643.08447 nm	209000	Fe I	emission	3d7.(4P).4s a 5P → 3d7.(4F).4p y 5D*	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Covalent radius (Pyykkö, triple)

Covalent radius (Bragg)

Van der Waals Radii

Batsanov

Alvarez

UFF

MM3

Atomic & Metallic Radii

Atomic radius (Rahm)

Metallic radius (C12)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Miedema

Gunnarsson–Lundqvist

Robles–Bartolotti

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

C₆

C₆ (Gould–Bučko)

Chemical Affinity

Proton affinity

Gas basicity

Miedema Parameters

Miedema molar volume

Miedema electron density

Supply Risk & Economics

Production concentration

Relative supply risk

Reserve distribution

Political stability (top producer)

Political stability (top reserve)

Phase Transitions & Allotropes

Melting point	1811.15 K
Boiling point	3134.15 K
Critical point (temperature)	9340.15 K

Oxidation State Categories

0 extended

+1 extended

+3 main

+7 extended

+4 extended

−4 extended

+5 extended

−2 extended

−1 extended

+6 extended

+2 main

Advanced Reference Data

Screening Constants (7)

n	Orbital	σ
1	s	0.619
2	p	3.9112
2	s	7.401
3	d	14.8202
3	p	13.2221
3	s	12.3239
4	s	20.566

Crystal Radii Detail (12)

Charge	CN	Spin	r_crystal (pm)	Origin
2	IV	HS	77
2	IVSQ	HS	78
2	VI	LS	75	estimated,
2	VI	HS	92	from r^3 vs V plots,
2	VIII	HS	106	calculated,
3	IV	HS	63
3	V		72
3	VI	LS	69	from r^3 vs V plots,
3	VI	HS	78.5	from r^3 vs V plots,
3	VIII	HS	92

Isotope Decay Modes (55)

Isotope	Mode	Intensity
45	2p	70%
45	B+	30%
45	B+p	18.9%
45	2p	7.8%
46	B+	100%
46	B+p	78.7%
46	2p	—
47	B+	100%
47	B+p	88.4%
48	B+	100%

X‑ray Scattering Factors (504)

Energy (eV)	f₁	f₂
10	—	1.37852
10.1617	—	1.42961
10.3261	—	1.48259
10.4931	—	1.53754
10.6628	—	1.59453
10.8353	—	1.65362
11.0106	—	1.71491
11.1886	—	1.77847
11.3696	—	1.84438
11.5535	—	1.91274

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

5.63×104 milligrams per kilogram

References (1)

[5] Iron https://education.jlab.org/itselemental/ele026.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

2×10-3 milligrams per liter

References (1)

[5] Iron https://education.jlab.org/itselemental/ele026.html

Sources

Sources of this element.

Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Its nuclei are very stable. Iron is a principal component of a meteorite class known as siderites and is a minor constituent of the other two meteorite classes. The core of the earth 2150 miles in radius is thought to be largely composed of iron with about 10 percent occluded hydrogen. The metal is the fourth most abundant element, by weight that makes up the crust of the earth.

The most common ore is hematite, which is frequently seen as black sands along beaches and banks of streams.

References (1)

[6] Iron https://periodic.lanl.gov/26.shtml

References

(9)

1 PubChem

Data deposited in or computed by PubChem

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2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

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3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

Iron

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

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4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

Visit source License

License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.

5 Jefferson Lab, U.S. Department of Energy

Iron

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

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License note: Please see citation and linking information: https://education.jlab.org/faq/index.html

6 Los Alamos National Laboratory, U.S. Department of Energy

Iron

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

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7 NIST Physical Measurement Laboratory

Iron

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

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8 PubChem Elements

Iron

This section provides all form of data related to element Iron.

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9 PubChem Elements

Iron

The element property data was retrieved from publications.

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Last updated: May 1, 2026

Data verified: May 12, 2026

Content is reviewed against latest scientific data.