Iron (Fe)
“The metal that taught civilisation to build — and the atom riding in your blood, ferrying every breath of oxygen from lungs to toes.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- Configuration [Ar] 3d⁶ 4s² — a Period 4, Group 8 d-block transition metal; losing the two 4s electrons (or one 3d more) gives the familiar Fe²⁺ and Fe³⁺ ions of green and brown salts.
- Rusts only when oxygen and moisture attack together: damp air paints it flaky orange-brown with hydrated iron(III) oxide, Fe₂O₃·xH₂O — salt and acid speed the ruin, which is why ships and coastal railings corrode fastest.
- One of just three elements — with cobalt and nickel — strongly magnetic at room temperature; heat it beyond 770 °C and the magnetism vanishes.
- Staggeringly abundant: iron and nickel make up most of the Earth’s core, and the churning of that molten iron generates the planet’s magnetic field; in the crust iron is the second most abundant metal after aluminium.
A silvery-grey metal with a bright lustre when freshly cut or polished, though it soon dulls in damp air. Pure iron is surprisingly soft and easily magnetised; it is the carbon mixed in that turns it into hard steel — the strong, tough form in which you always meet it.
Where you meet it
✦ Uses
- Reinforcing concrete — every RCC pillar, beam and slab in Bangladesh, from village homes to the Padma Bridge, is poured around a skeleton of steel rods, because concrete is strong in compression but weak in tension.
- Stainless steel — iron alloyed with about 18% chromium and 8% nickel makes the rust-proof cutlery, sinks, hospital instruments and water tanks of everyday life.
- Railway lines, ship plates, girders and agricultural tools — steel in its countless grades remains, by a huge margin, the most-used metal on Earth.
- Iron-folic acid tablets — Bangladesh’s school health programme gives weekly iron tablets to adolescent girls because iron is the core of haemoglobin, the protein that carries oxygen in the blood.
◍ Everyday examples
- A drop of your own blood — each of its millions of red cells carries about 270 million haemoglobin molecules, every one built around an iron atom.
- The rods poking out of any half-finished building, the rail line at a level crossing and the karai in the kitchen are all iron at different strengths.
- Spinach, lentils and dates — the iron a Bengali plate draws from dal and shak replenishes the few milligrams the body loses every day.
History & name
Iron is the only everyday metal with no discoverer: long before anyone could smelt it, people picked up black nuggets of meteoric iron and hammered them into beads and daggers — the blade of Tutankhamun’s 3,300-year-old dagger fell from the sky. Around 1200 BCE smiths in the Middle East learned to pull iron from its ore by heating it with charcoal, and the cheap, strong metal ended the Bronze Age and gave the age that followed its name. The English word descends from Old English īsern, but chemists everywhere write Fe, from the Latin ferrum. From the ploughshare to the rebar inside every modern building, the smelting of iron is often called the invention that changed everything.