Iron

Iron is the chemical element with atomic number 26 and the symbol Fe. It is a shiny, grayish metal in group 8 of the periodic table that rusts in damp air. Even so, it is the most important of all metals: about 90 percent of the metal refined today is iron, most of it made into steel.

History of iron

Iron has been used for thousands of years, and no single discoverer is recorded. Iron objects found in Egypt that date from around 3500 BC contain about 7.5 percent nickel, which shows they were made from meteorites, because iron from space is naturally alloyed with nickel.

The ancient Hittites of Asia Minor, in modern Turkey, were the first to smelt iron from its ores, around 1500 BC. Smelting means heating an ore with other materials so that the metal separates from it. The new metal was stronger than bronze and gave the Hittites economic and political power, and the Iron Age had begun.

Some kinds of iron were clearly better than others, depending on how much carbon they contained, although this was not understood at first. Some iron ore also contained vanadium, which produced the so-called Damascene steel that was ideal for swords. In 1722 the French scientist Rene Antoine Ferchault de Reaumur wrote the first book explaining that steel, wrought iron and cast iron differ in how much charcoal, or carbon, they contain. The Industrial Revolution, which began that same century, relied heavily on the metal. The name comes from the Anglo-Saxon word iren.

Properties of iron

Iron has a standard atomic weight of 55.845, and NIST lists the same value with an uncertainty of 2 in the last digit. An iron atom has 26 protons and an electron configuration of [Ar] 4s2 3d6, meaning the arrangement of argon plus two electrons in the 4s level and six in the 3d level.

At room temperature iron is a solid with a density of 7.874 grams per cubic centimeter. PubChem gives a melting point of 1,811 kelvins, about 1,538 degrees Celsius, and a boiling point of 3,134 kelvins, about 2,861 degrees Celsius. Iron is a transition metal, and its common oxidation states are plus 3 and plus 2. An oxidation state is a number that tracks how many electrons an atom has lost or shared in a compound.

PubChem also records an electronegativity of 1.83 on the Pauling scale, a first ionization energy of 7.902 electronvolts and an atomic radius of 194 picometers. The Royal Society of Chemistry calls iron an enigma, since the metal rusts easily and yet serves as the backbone of so much construction and manufacturing.

Occurrence and production of iron

Iron is the fourth most abundant element by mass in the Earth’s crust. The core of the Earth is thought to be made largely of iron together with nickel and sulfur. The most common iron-containing ore is hematite, but the metal is also widespread in minerals such as magnetite and taconite.

Commercially, iron is produced in a blast furnace by heating hematite or magnetite with coke, a form of carbon, and limestone, which is calcium carbonate. This produces pig iron, which contains about 3 percent carbon and other impurities and is used mainly to make steel. The Royal Society of Chemistry puts world production at around 1.3 billion tonnes of crude steel each year.

Uses of iron

Most iron is used to manufacture steel for civil engineering, such as reinforced concrete and girders, and for manufacturing. Ordinary carbon steel is an alloy of iron with carbon, from 0.1 percent in mild steel up to 2 percent in high-carbon steels. Alloy steels add nickel, chromium, vanadium, tungsten or manganese, and they are stronger and tougher. They are used in bridges, electricity pylons, bicycle chains, cutting tools and rifle barrels.

Stainless steel resists corrosion and contains at least 10.5 percent chromium. Nickel, molybdenum, titanium and copper may be added to improve strength and workability, and the result is used in architecture, bearings, cutlery and surgical instruments. Cast iron contains 3 to 5 percent carbon. It is cheaper but less tough than steel, and it is used for pipes, valves and pumps. Magnets can also be made from iron and its alloys and compounds.

Iron catalysts are used in the Haber process for producing ammonia and in the Fischer-Tropsch process, which converts syngas, a mix of hydrogen and carbon monoxide, into liquid fuels.

The wide range of steels shows how small changes in composition alter the properties of the metal. Mild steel holds as little as 0.1 percent carbon and high-carbon steels up to 2 percent, while cast iron holds 3 to 5 percent. The Royal Society of Chemistry notes that, as a result, iron products range from tough girders and cutting tools to cheaper pipes, valves and pumps.

Isotopes of iron

NIST lists four stable isotopes of iron: iron-54, iron-56, iron-57 and iron-58. Iron-56 is by far the most abundant at about 91.754 percent of natural iron. Iron-54 accounts for about 5.845 percent, iron-57 for about 2.119 percent and iron-58 for about 0.282 percent. The number after each name is the combined count of protons and neutrons in the atom.

Iron in life and the environment

Iron is an essential element for all forms of life. The average human contains about 4 grams of it, and much of that is in hemoglobin, the protein in blood that carries oxygen from the lungs to cells, where it is needed for tissue respiration. The Royal Society of Chemistry states that humans need 10 to 18 milligrams of iron each day and that a lack of iron causes anemia. Foods such as liver, kidney, molasses, brewer’s yeast and cocoa contain a lot of it.

In the environment, iron reacts with oxygen and moisture to form rust, which is why unprotected iron and steel deteriorate in damp air. The information here is general background rather than health advice.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue