Quick Facts
| Property | Value |
|---|---|
| Symbol | Fe |
| Atomic Number | 26 |
| Atomic Mass | 55.845 u |
| Category | Transition Metal |
| Period | 4 |
| Group | 8 |
| Block | d |
| Electron Configuration | [Ar] 3d⁶ 4s² |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 7.874 g/cm³ |
| Melting Point | 1538°C (1811 K) |
| Boiling Point | 2861°C (3134 K) |
| Appearance | Lustrous, silvery-gray metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Ar] 3d⁶ 4s² |
| Electronegativity | 1.83 (Pauling scale) |
| First Ionization Energy | 762.5 kJ/mol |
| Atomic Radius | 126 pm |
| Covalent Radius | 132 pm |
| Van der Waals Radius | 194 pm |
History and Discovery
Discovered by: Known since antiquity Year of Discovery: ~3500 BCE Location: Various ancient civilizations
Etymology
The symbol "Fe" comes from Latin "ferrum" meaning iron. The English word "iron" comes from Old English "īsern" or "īren," related to Celtic and Germanic words.
Discovery Story
Iron has been known since the earliest civilizations. Meteoric iron was used before smelting was developed. The Iron Age began around 1200 BCE when iron smelting became widespread. The Hittites may have been among the first to smelt iron systematically.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ⁵⁴Fe | 5.85% | Stable | - |
| ⁵⁶Fe | 91.75% | Stable | - |
| ⁵⁷Fe | 2.12% | Stable | - |
| ⁵⁸Fe | 0.28% | Stable | - |
Occurrence
Natural Abundance
Iron is the fourth most abundant element in Earth's crust (5%) and the most abundant element on Earth overall (32% by mass, concentrated in the core). Major ores are hematite (Fe₂O₃) and magnetite (Fe₃O₄). Major producers are Australia, Brazil, China, and India.
Extraction and Production
- Blast Furnace: Reduction of ore with coke (primary method)
- Direct Reduction: For steel production
- Sources: Iron ore mining
- Global production: about 2.5 billion tons of iron ore annually
Applications and Uses
Construction and Infrastructure
- Structural steel for buildings and bridges
- Reinforcing bars (rebar) for concrete
- Railway tracks
- Pipes and tubes
Transportation
- Automobile bodies and engines
- Ships and shipbuilding
- Railway equipment
- Aircraft landing gear
Machinery and Tools
- Machine tools
- Industrial equipment
- Hand tools
- Farm equipment
Other Uses
- Cast iron cookware
- Magnets
- Catalysts
- Pigments (iron oxides)
Biological Role
Iron is essential for almost all living organisms. It is central to oxygen transport and cellular respiration.
In the Human Body
- About 4 g in adult body
- 65% in hemoglobin (oxygen transport)
- Found in myoglobin (muscle oxygen storage)
- Essential for electron transport chain
- Daily requirement: 8-18 mg
Dietary Sources
Red meat, poultry, fish, legumes, spinach, and fortified cereals are iron sources. Heme iron (from meat) is better absorbed.
Safety and Hazards
Toxicity
Iron is generally safe but excess causes iron overload (hemochromatosis). Iron supplements can be toxic in overdose, especially for children.
Handling Precautions
- Fine iron powder is pyrophoric (can ignite spontaneously)
- Iron rusts in moist air
- Molten iron requires extreme caution
- Cutting and welding produce hazardous fumes
Environmental Impact
Iron mining has significant environmental impacts. Iron itself is not toxic to ecosystems. Acid mine drainage can release iron and other contaminants.
Interesting Facts
- Iron-56 has the most stable nucleus of any element (highest binding energy per nucleon)
- Earth's core is primarily iron, creating our magnetic field
- Blood is red because of iron in hemoglobin
- Iron is formed in massive stars and released in supernovae
- The Eiffel Tower contains about 7,300 tons of iron