- Iron (Fe) is a lustrous, silvery-gray transition metal with atomic number 26, positioned in Group 8 of the periodic table.
- It has eight valence electrons—two in the 4s subshell and six in the 3d subshell—and commonly exhibits oxidation states of +2 and +3, although other states ranging from −2 to +6 are known. Its atomic structure consists of twenty-six protons, typically thirty neutrons, and twenty-six electrons arranged in four shells.
- Naturally occurring iron is composed mainly of the stable isotope iron-56 (⁵⁶Fe), which accounts for about 91.75% of natural iron, along with iron-54 (⁵⁴Fe), iron-57 (⁵⁷Fe), and iron-58 (⁵⁸Fe).
- Iron is the most abundant element on Earth by mass, making up about 35% of the planet’s total mass, most of it concentrated in the core. It is the fourth most abundant element in the Earth’s crust. In nature, iron occurs primarily as oxides, such as hematite (Fe₂O₃), magnetite (Fe₃O₄), limonite (FeO(OH)·nH₂O), and siderite (FeCO₃). Major iron ore deposits are found in Australia, Brazil, Russia, and China. Iron is rarely found in pure metallic form on Earth’s surface, except in meteorites, where it occurs as iron-nickel alloys such as kamacite and taenite.
- The use of iron dates back thousands of years, marking the transition from the Bronze Age to the Iron Age around 1200 BCE. The smelting of iron from its ores revolutionized tools, weapons, and architecture. The name “iron” derives from Old English īsern, with its chemical symbol “Fe” coming from the Latin ferrum.
- Iron’s most important industrial application is in the production of steel—an alloy of iron with carbon and often other elements such as manganese, chromium, or nickel. Steel is strong, versatile, and relatively inexpensive, making it the most widely used metal in construction, transportation, machinery, and countless other applications. Cast iron, which contains a higher carbon content, is used in heavy-duty items like pipes, engine blocks, and cookware, while wrought iron, with very low carbon content, is valued for decorative and structural uses.
- Chemically, iron is reactive and readily oxidizes in moist air, forming iron oxides (rust), which are porous and flake off, exposing fresh metal to further corrosion. This tendency is countered in alloys like stainless steel, where chromium forms a protective oxide layer. Iron compounds occur in many forms: Fe²⁺ compounds are typically pale green, while Fe³⁺ compounds are often brown or yellow.
- Biologically, iron is an essential element for almost all living organisms. In humans, it is a critical component of hemoglobin, the oxygen-carrying protein in red blood cells, and myoglobin, which stores oxygen in muscle tissue. Iron is also a cofactor in many enzymes involved in metabolism and electron transport. Dietary iron deficiency can cause anemia, characterized by fatigue and weakness, while excess iron can lead to conditions such as hemochromatosis, which damages organs.
- In the broader context of the universe, iron is notable for being the most stable nucleus in terms of binding energy per nucleon, meaning elements heavier than iron generally require energy input to form. Most of the iron in the universe is created in massive stars and distributed by supernova explosions.
- Environmentally, iron is not generally toxic in natural concentrations, but industrial waste and acid mine drainage can release large amounts of dissolved iron into water systems, sometimes harming aquatic life. However, in many soils and sediments, iron acts as an important chemical buffer.
