Periodic table › Iron
1. Identity and classification
Lustrous metallic solid with a grayish-silver tinge; oxidizes in moist air to reddish-brown rust
- Name and symbol
- Iron (Iron) · Fe
- Atomic number
- 26
- Relative atomic weight / mass number
- 55.845 ± 0.002
- Group · period · block
- 8 · 4 · d
- Category
- Transition Metal
- State near room temperature
- Solid
- Stable isotopes
- At least one stable isotope
- CAS number
- 7439-89-6
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 26 · 26
- Neutrons in reference isotope
- 30 (56Fe)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²- Abbreviated configuration
[Ar]4s² 3d⁶- Electrons per shell
- 2, 8, 14, 2
- Listed oxidation states
- +3, +2
- Electronegativity
- 1.83 (Pauling)
- First ionization energy
- 762.427 kJ/mol · 7.902 eV
- Electron affinity
- 15.727 kJ/mol
- Covalent radius
- 132 pm
- van der Waals radius
- 194 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 7.874 g/cm³
- Melting point
- 1811 K · 1537.85 °C · 2800.13 °F
- Boiling point
- 3134 K · 2860.85 °C · 5181.53 °F
- Crystal structure
- BCC
- Specific heat
- 0.449 J/(g·K)
- Thermal conductivity
- 80.4 W/(m·K)
- Enthalpy of fusion
- 13.81 kJ/mol
- Enthalpy of vaporization
- 340 kJ/mol
- Magnetic ordering
- Ferromagnetic
- Mohs hardness
- 4
- Speed of sound
- 5120 m/s
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The +2 and +3 oxidation states are common; iron is central to many alloys and biological proteins.
Selected compounds: Fe₂O₃ (Hematite / Rust) · Fe₃O₄ (Magnetite) · FeSO₄ (Iron(II) sulfate) · FeCl₃ (Iron(III) chloride)
Reaction reference
Rusting requires oxygen and moisture; protective coatings can slow corrosion.
No rapid reaction with cold water; hot steam can react with iron.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 54Fe | Stable | 5.845% | Stable |
| 56Fe | Stable | 91.754% | Stable |
| 57Fe | Stable | 2.119% | Stable |
| 58Fe | Stable | 0.282% | Stable |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- Known since antiquity; no exact discovery year
- Scientists associated with discovery
- Known since antiquity
- Location
- Ancient Anatolia, Egypt & India
- Origin
- Natural
- Listed crustal abundance
- 56300 ppm
Minerals and naming reference
Hematite (Fe₂O₃), Magnetite (Fe₃O₄), Goethite, Limonite, Siderite (FeCO₃), Pyrite (FeS₂)
From Anglo-Saxon 'iren', likely derived from Proto-Celtic 'isarnon' meaning holy or strong metal; symbol Fe from Latin 'ferrum'
7. Applications
Cast-iron cookware, stainless steel cutlery, appliances, nails, tools, and bicycles
Detailed applications by field
- everyday
- Cast-iron cookware, stainless steel cutlery, appliances, nails, tools, and bicycles
- industry
- Carbon steel and alloy steel for bridges, skyscrapers, ships, railways, and heavy machinery
- electronics
- Transformer cores, inductors, electric motor stators, NdFeB permanent magnets
- medicine
- Ferrous sulfate supplements for iron-deficiency anemia; superparamagnetic iron oxide nanoparticles (SPIONs) for MRI contrast
- energy
- Wind turbine generators, hydroelectric turbines, Lithium Iron Phosphate (LiFePO₄ / LFP) EV batteries
- aerospace
- High-strength maraging steels for rocket motor casings and aircraft landing gear
- agriculture
- Chelated iron (Fe-EDTA) micronutrient fertilizers to prevent chlorosis in crops
- science
- ⁵⁷Fe Mössbauer spectroscopy in mineralogy and planetary exploration (Mars rovers)
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Central atom in the heme group of hemoglobin and myoglobin for oxygen transport, and in cytochromes and iron-sulfur proteins for cellular respiration.