Iron Element Properties
Complete reference for Iron (Fe, element 26): atomic data, electron configuration, isotopes, physical constants, and a property unit converter.
Use the Iron Element Properties
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 above ruthenium (Z=44) and 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
Iron is a lustrous silvery-gray transition metal with atomic number 26 and symbol Fe (from Latin ferrum), located in Period 4, Group 8 of the periodic table. It is the most abundant element on Earth by mass and the fourth most abundant in the crust (~5%). Iron is the primary component of Earth's core and the backbone of modern industrial civilization through steel production. This reference compiles the essential physical constants, electron configuration, isotope data, chemical properties, and common compounds of iron, along with an interactive 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.