Iron Element Properties
Complete reference for Iron (Fe, element 26): atomic data, electron configuration, isotopes, physical constants, and a property unit converter.
Iron
Transition Metal — Period 4, Group 8
Atomic Identity
Periodic Table Locator — Period 4 Neighborhood (d-block)
Iron (Z=26) sits between manganese (Z=25) and cobalt (Z=27) in Period 4. It is directly below ruthenium (Z=44) and above osmium (Z=76) in Group 8 of the d-block.
Electron Configuration
4 unpaired 3d electrons → attracted to magnetic fields
Key Isotopes of Iron
| Isotope | Symbol | Protons | Neutrons | Mass (u) | Natural Abundance | Stability |
|---|---|---|---|---|---|---|
| Iron-54 | ⁵⁴Fe | 26 | 28 | 53.9396090 | 5.845% | Stable |
| Iron-55 | ⁵⁵Fe | 26 | 29 | 54.9382934 | Radioactive |
Unstable
Electron capture, t½ = 2.73 yr |
| Iron-56 | ⁵⁶Fe | 26 | 30 | 55.9349363 | 91.754% | Stable |
| Iron-57 | ⁵⁷Fe | 26 | 31 | 56.9353928 | 2.119% | Stable |
| Iron-58 | ⁵⁸Fe | 26 | 32 | 57.9332744 | 0.282% | Stable |
| Iron-59 | ⁵⁹Fe | 26 | 33 | 58.9348755 | Radioactive |
Unstable
β⁻ decay, t½ = 44.5 d |
| Iron-60 | ⁶⁰Fe | 26 | 34 | 59.9340707 | Radioactive |
Unstable
β⁻ decay, t½ = 2.6 × 10⁶ yr |
Fe-56 dominates at ~91.75% natural abundance and has among the highest binding energies per nucleon (8.7906 MeV; Ni-62 holds the record at 8.7945 MeV). Fe-57 is uniquely important for Mossbauer spectroscopy due to its 14.4 keV gamma transition. Fe-60 is a long-lived radionuclide found in deep-sea sediments from nearby supernova events.
Physical Properties
Chemical Properties
Oxidation States of Iron
| State | Ion / Form | Example Compound | Notes |
|---|---|---|---|
| 0 | Fe⁰ | Fe(CO)₅ (iron pentacarbonyl) | Typical in organometallic compounds |
| +2 | Fe²⁺ (ferrous) | FeSO₄ (green vitriol), FeCl₂, FeO | Most common; found in hemoglobin |
| +3 | Fe³⁺ (ferric) | Fe₂O₃ (rust), FeCl₃, Fe(OH)₃ | Most stable in oxidizing conditions |
| +4 | Fe(IV) | FeO₂ (iron(IV) oxide, rare) | Found in some biological enzymes |
| +6 | FeO₄²⁻ (ferrate) | K₂FeO₄ (potassium ferrate) | Powerful oxidant; water treatment use |
Ground State Quantum Numbers
Notable Emission Lines
Iron has an exceptionally complex emission spectrum with over 4000 known lines — useful as a wavelength calibration standard in spectroscopy. In a flame test, iron produces an orange-gold color.
Property Unit Converter
Convert common iron property values between units. Enter a value and select the conversion.
Common Iron Compounds
| Compound | Formula | Common Name | Key Uses |
|---|---|---|---|
| Iron(III) oxide | Fe₂O₃ | Rust / hematite | Pigment (red ochre), steelmaking ore, magnetic media |
| Iron(II,III) oxide | Fe₃O₄ | Magnetite / lodestone | Natural magnet, magnetic recording, iron ore |
| Iron(II) sulfate | FeSO₄·7H₂O | Green vitriol | Iron supplement, water treatment, mordant for dyes |
| Iron(III) chloride | FeCl₃ | Ferric chloride | PCB etching, water treatment coagulant, Lewis acid |
| Iron(II) carbonate | FeCO₃ | Siderite | Iron ore mineral, dietary supplements |
| Iron(III) oxide-hydroxide | FeO(OH) | Goethite / rust | Brown pigment, soil mineral, rust patina |
| Iron(II) disulfide | FeS₂ | Pyrite (fool's gold) | Sulfuric acid production, lithium batteries |
| Iron pentacarbonyl | Fe(CO)₅ | — | Organometallic reagent, iron powder production |
Key Facts About Iron
Most Abundant Element on Earth
By total mass, iron is the most abundant element on Earth (~32%), concentrated in the iron-nickel core. In the crust it ranks fourth at ~5% by mass. Earth's solid inner core (radius ~1220 km) and liquid outer core are primarily iron-nickel alloy, generating Earth's magnetic field through the geodynamo effect.
Foundation of the Iron Age
The Iron Age (~1200 BCE onward) marks humanity's shift from bronze to iron tools and weapons. Pure iron is soft, but carbon-alloyed iron (steel) is vastly stronger. Modern civilization produces over 1.8 billion tonnes of crude steel per year — roughly 90% of all metal produced globally — making iron the most economically important metal.
Essential for Life: Hemoglobin
Iron is the active-site element of hemoglobin and myoglobin. Fe²⁺ in the heme porphyrin ring reversibly binds O₂, enabling oxygen transport in blood and storage in muscle. The average adult human body contains ~3–4 g of iron, of which ~70% is in hemoglobin. Iron deficiency anemia affects an estimated 1.62 billion people worldwide.
Fe-56: Near the Binding Energy Peak
Fe-56 is among the highest binding energies per nucleon (8.7906 MeV/nucleon), though Ni-62 holds the record at 8.7945 MeV/nucleon. Fe-56 dominates stellar iron-group abundances due to nuclear statistical equilibrium, not because it is the absolute maximum. When a massive star's core becomes mostly iron-group nuclei, further fusion yields no net energy, the core collapses under gravity, and the star explodes as a Type II supernova — scattering heavier elements through space.
Ferromagnetism Below 770 °C
Iron is one of three naturally ferromagnetic elements (with cobalt and nickel). Below its Curie temperature of 770 °C, iron's 3d magnetic domains align in an external field and retain magnetization. Above 770 °C, thermal energy randomizes the domains and iron becomes paramagnetic (alpha to delta phase transition at 912 °C is a separate crystal change).
Polymorphic Crystal Structures
Pure iron exists in multiple allotropic (polymorphic) forms depending on temperature: alpha-iron (BCC, ferromagnetic, below 912 °C), gamma-iron (FCC, paramagnetic, 912–1394 °C — this phase dissolves carbon to form austenite in steel), delta-iron (BCC, 1394–1538 °C), and the liquid phase above 1538 °C. These phase transitions are exploited in heat treatment of steel (quenching, annealing, tempering).
Summary
Complete reference for Iron (Fe, element 26): atomic data, electron configuration, isotopes, physical constants, and a property unit converter.
How it works
- Browse the atomic identity card for symbol, atomic number, and standard atomic weight.
- Check the electron configuration panel for orbital notation and quantum numbers.
- Review the isotopes table for stable and notable radioactive isotopes with natural abundances.
- Consult the physical and chemical properties panels for melting point, density, ionization energies, and oxidation states.
- Use the interactive unit converter to convert iron property values between common units.
- Explore the key facts section for industrial context and interesting chemistry of iron.
Use cases
- Look up iron constants for chemistry homework, metallurgy, or materials science work.
- Verify atomic data when writing lab reports or research papers.
- Reference isotope data for Mossbauer spectroscopy or geochronology research.
- Convert melting and boiling points between Celsius, Fahrenheit, and Kelvin.
- Study transition metal electron configurations using iron as a canonical example.
- Confirm oxidation states (+2, +3) for writing ionic formulae or balancing redox equations.
- Research iron compounds for industrial chemistry, biology, or environmental science.
- Quick-reference ionization energies for electrochemistry or spectroscopy calculations.