Iron (Fe)

Iron (symbol Fe) is the chemical element with atomic number 26: a transition metal, solid at 0 °C, with an atomic mass of 55.845 u. Known since antiquity.

Iron is the most abundant element on Earth by mass, because it makes up most of the planet's core. Alloyed with a little carbon, it becomes steel, humanity's most widely used material. In our blood, every hemoglobin molecule holds four iron atoms that carry oxygen. In stars, it marks the end of energy-producing nuclear fusion.

Key facts

Atomic number: 26
Symbol: Fe
French name: Fer
Atomic mass: 55.845 u
Molar mass: 55.845 g/mol
Family: Transition metals
Position: period 4, group 8, d-block
State at 0 °C: Solid
Melting point: 1,537.9 °C
Boiling point: 2,860.9 °C
Density: 7.87 g/cm³
Electronegativity (Pauling): 1.83
First ionization energy: 763 kJ/mol
Atomic radius: 140 pm
Electron configuration: [Ar] 3d⁶ 4s²
Abundance in Earth's crust: 56,300 ppm (4th most abundant element)
Indicative price: 0.42 $/kg (order of magnitude)
Radioactive: no
Discovery: Antiquity

Origin of the name

From the Old English īren; the symbol Fe comes from the Latin ferrum.

What does iron look like?

A silvery-gray metal, shiny when polished, attracted by magnets. In damp air it develops flaking reddish-brown rust.

Where is iron found?

About 32% of the mass of the whole Earth and 5.6% of the crust (the fourth most abundant element). The human body contains about 4 g, two thirds of it in hemoglobin. Red soils and the planet Mars owe their color to iron oxides.

Natural sources

Hematite
Magnetite
Goethite
Siderite
Limonite

How is iron produced?

About 2.5 billion tonnes of iron ore are mined each year. It is reduced with coke in blast furnaces to make pig iron, which is turned into steel; more and more steel is also made by melting scrap in electric furnaces. Steel output is around 1.9 billion tonnes a year, more than half of it in China.

Top producers

Australia
Brazil
China
India

What is iron used for?

Structural steel: buildings, bridges, rails.
Cars, ships and machinery.
Cast iron for pans, pipes and castings.
Electrical steel sheets in transformers and motors.
Catalyst for ammonia synthesis.
Supplements for anemia.

In everyday life

A cast-iron skillet
Nails, screws and paper clips
The body of your car
Spinach and lentils
Fridge magnets stuck to the steel door

Role in living things

Essential: it carries oxygen in the blood's hemoglobin and the muscles' myoglobin, and takes part in energy production in the mitochondria. Iron deficiency is the most widespread nutritional deficiency in the world and causes anemia.

Hazards of iron

Iron overload, notably from hereditary hemochromatosis (common in people of Breton or Celtic descent), damages the liver and heart. Accidental swallowing of iron tablets is a classic cause of serious poisoning in young children.

Cosmic origin

White dwarfs: Produced by the thermonuclear explosion of a white dwarf (type Ia supernova).
Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of iron

The first iron objects, more than 5,000 years ago, were cut from meteorites. Ironworking spread across the Near East around 1200 BCE, ushering in the Iron Age. The blast furnace, then the Bessemer process (1856), made steel the material of the Industrial Revolution.

Did you know?

The dagger found in Tutankhamun's tomb was forged from meteoritic iron, as analyses confirmed in 2016.
The Eiffel Tower is made of about 7,300 tonnes of puddled iron, held together by 2.5 million rivets.
When the core of a massive star fills with iron, fusion no longer releases energy: the star collapses and explodes as a supernova.
Earth's magnetic field is generated by the motion of liquid iron in the outer core.

Isotopes of iron

Four stable isotopes, including iron-56, one of the most tightly bound nuclei of all: that's why massive stars stop at iron. Iron-60 found on the ocean floor is the signature of nearby supernovae.

iron-54: 5.845% of natural iron, stable
iron-55: radioactive, half-life 2.74 years. X-ray source for X-ray fluorescence analysis and calibration.
iron-56: 91.754% of natural iron, stable. The end point of fusion inside massive stars.
iron-57: 2.119% of natural iron, stable. The basis of Mössbauer spectroscopy, which analyzed rocks on Mars.
iron-58: 0.282% of natural iron, stable. Stable tracer for studying iron absorption and anemia.
iron-59: radioactive, half-life 44.5 days. Tracer of iron metabolism in the blood.
iron-60: radioactive, half-life 2.62 × 10⁶ years. Found in ocean crusts and Antarctic snow, it bears witness to nearby supernovae a few million years ago.

Common compounds

Rust (Fe₂O₃) · Pyrite (FeS₂) · Lithium iron phosphate (LiFePO₄) · Neodymium magnet (Nd₂Fe₁₄B)

Related elements

Same family (transition metals): Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Yttrium (Y), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Rhenium (Re), Osmium (Os), Iridium (Ir), Platinum (Pt), Gold (Au), Mercury (Hg), Rutherfordium (Rf), Dubnium (Db), Seaborgium (Sg), Bohrium (Bh), Hassium (Hs).

Same column (group 8): Ruthenium (Ru), Osmium (Os), Hassium (Hs).