Iron
Atomic Data
| Atomic Number | 26 |
| Symbol | Fe |
| Atomic Weight | 55.845 u |
| Density (STP) | 7.874 g/cm³ |
| Melting Point | 1537.85 °C (1811 K) |
| Boiling Point | 2860.85 °C (3134 K) |
| Electronegativity | 1.83 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d6 4s2 |
| Oxidation States | +2, +3, +6 |
| Phase at STP | Solid |
| Category | Transition Metal |
| Period / Group | 4 / 8 |
| CAS Number | 7439-89-6 |
Electron Configuration
[Ar] 3d6 4s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 6 | 24 |
| N | 4 | 4s | 2 | 26 |
| Total | 26 | 26 | ||
Isotopes of Iron
Iron has four naturally occurring stable isotopes. The most abundant is ⁵⁶Fe, comprising 91.754% of all naturally occurring Iron.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Iron-54 | ⁵⁴Fe | 26 | 28 | 5.845 | Stable |
| Iron-56 | ⁵⁶Fe | 26 | 30 | 91.754 | Stable |
| Iron-57 | ⁵⁷Fe | 26 | 31 | 2.119 | Stable |
| Iron-58 | ⁵⁸Fe | 26 | 32 | 0.282 | Stable |
Abundance & Occurrence
Iron is present in Earth's crust at approximately 56300 ppm by mass and at approximately 110000 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Iron dust and fume: siderosis: Prolonged inhalation of iron oxide dust or fumes causes siderosis, a benign pneumoconiosis; while generally non-progressive, heavy exposures may predispose to other lung diseases.
- Welding fumes: Welding on iron and steel produces fumes containing iron oxides; IARC classifies welding fumes as Group 1 carcinogens: local exhaust ventilation is required at all welding operations.
- Iron powder fire hazard: Finely divided iron powder is flammable and can ignite spontaneously if freshly reduced; bulk iron does not pose a fire hazard under normal conditions.
- Corrosion and structural safety: Rusting iron loses structural integrity; inspect iron structures regularly for corrosion, especially in wet or salt environments, to avoid structural failure.
Iron in the Real World
Real-World Uses
- Steel and cast iron: Iron is the primary component of steel (iron with 0.02–2.1% carbon) and cast iron (>2.1% carbon), the most widely used structural metals in construction, machinery, vehicles, railways, and appliances.
- Electromagnetic cores: Laminated silicon iron (electrical steel) cores concentrate and guide magnetic flux in electric motors, generators, and transformers with minimal eddy current losses, underpinning the global electricity infrastructure.
- Catalysis: Iron is the catalyst in the Haber-Bosch process for ammonia synthesis, promoted by potassium and alumina; it is also used in Fischer-Tropsch synthesis to convert syngas into liquid fuels.
- Biomedical and nutritional: Iron is the central atom of haemoglobin and myoglobin, enabling oxygen transport and storage in vertebrate blood and muscle; iron supplements treat iron-deficiency anaemia, the most common nutritional deficiency worldwide.
- Pigments: Iron oxide pigments (ochres, siennas, umbers) provide yellow, red, brown, and black colours in paints, ceramics, cosmetics, and construction materials and are among the most lightfast and non-toxic pigments available.
- Fortified foods: Iron is added to flour, breakfast cereals, and infant formula as elemental iron, ferrous sulfate, or ferrous fumarate to prevent deficiency in populations with low dietary iron intake.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is iron used for?
Iron is the most widely used metal on Earth. As the main component of steel, it forms the structural backbone of buildings, bridges, ships, vehicles, and machinery. Cast iron is used for pipes, cookware, and engine blocks. Iron compounds are important in water treatment, and iron is an essential nutrient in human blood as the core of haemoglobin.
Is iron essential for life?
Yes, iron is essential for virtually all living organisms. In humans it is a critical component of haemoglobin, the protein in red blood cells that carries oxygen from the lungs to the body's tissues. Iron deficiency is the most common nutritional deficiency worldwide, causing anaemia. Most dietary iron comes from red meat, legumes, and leafy green vegetables.
How was iron discovered?
Iron has been used by humans for thousands of years. The earliest known iron artefacts, made from meteoritic iron, date to around 3500 BCE. Smelting of iron from ore began around 1200 BCE in the Middle East and Anatolia, marking the start of the Iron Age. Iron was so fundamental that it was known to virtually every ancient civilisation independently.
Why does iron rust?
Iron rusts because it reacts with oxygen and water in the environment. The iron atoms on the surface combine with oxygen to form iron oxides (primarily Fe2O3·xH2O), which form a loose, flaky layer that does not protect the underlying metal: unlike chromium oxide on stainless steel. This allows rusting to continue inward until the metal is consumed.