Iron

Iron is a chemical element with the symbol Fe, from the Latin word ferrum. It is a strong metal and one of the most common elements on Earth. It makes up much of our planet’s outer and inner core. Because it is so plentiful, iron has been very important throughout human history.

People learned how to work with iron around the year 1200 BC. This started the Iron Age. During this time, iron tools and weapons began replacing those made from copper alloys. This brought big changes to farming, building, and warfare. Today, iron is still very important. We use it to make many kinds of steel. Steel is used in cars, bridges, and cooking pans.

Pure iron looks shiny and silvery-gray, but it easily reacts with oxygen and water to form rust. Rust does not protect the iron, so more iron keeps rusting away. In living things, iron is very important too. Our bodies use it in special proteins that help carry oxygen in our blood and store it in our muscles. Without enough iron in our food, we can become sick and tired.

Characteristics

Main article: Allotropes of iron

Main article: Isotopes of iron

Iron is a special metal. Its atoms can arrange in different ways. When iron cools, its atoms change how they fit together. This creates different forms called allotropes. One form, alpha-iron, is common at normal pressures and temperatures. Another form, epsilon-iron, exists under very high pressure, like deep inside the Earth.

Iron has several stable forms, or isotopes, that occur naturally. The most common is called iron-56. Scientists study these isotopes to learn about how elements form in space and how planets develop. Iron-56 is important because it is the most common end product of processes that create elements in stars. It is the most abundant element in the Earth’s core and one of the most common elements in the universe.

Origin and occurrence in nature

Iron is very common in space, especially in planets like Earth. It was made during big explosions called Ia supernovae, which sent iron floating into space.

On Earth, we rarely find pure iron because it rusts quickly. But scientists think Earth’s inner and outer core are mostly made of iron mixed with nickel. This moving iron in the outer core helps make Earth’s magnetic field. Other planets such as Mercury, Venus, and Mars, as well as Earth’s Moon, are also believed to have iron inside them. Rare iron meteorites are the main way we find natural metal iron on Earth’s surface. These meteorites often have minerals like taenite and kamacite that are full of iron.

In Earth’s outer layer, called the crust, iron isn’t very common—it makes up only about 5% of the crust. Most of this iron is mixed with other elements to make minerals such as hematite, magnetite, and siderite. These minerals are important for getting iron. Iron is also found in special rocks called banded iron formations, which formed long ago, between 3,700 and 1,800 million years ago. Iron can color rocks and even whole areas, like the Painted Hills in Oregon.

Chemistry and compounds

Iron is a special kind of metal called a transition metal. It can form many different compounds because it can change how many electrons it shares with other atoms. One famous iron compound is ferrocene, which helped scientists learn more about these kinds of chemicals.

Iron usually forms compounds in two main ways: +2, called iron(II) or ferrous, and +3, called iron(III) or ferric. For example, potassium ferrate (K₂FeO₄) shows iron in the +6 state. These compounds have many uses, like in pigments and magnetic storage devices.

Iron also forms many coordination compounds, where it bonds with other molecules in special patterns. For example, Prussian blue is a well-known compound used as a blue pigment. Organometallic compounds, where iron bonds directly to carbon atoms, are also important. One famous example is ferrocene, a sandwich compound that has been very useful in chemistry.

History

Main article: History of ferrous metallurgy

Iron has been known and used by humans for thousands of years. Ancient people liked iron, especially from meteorites, because it came from the sky and could be made into strong tools and weapons. Over time, people learned how to get iron from rocks and ores. This led to the Iron Age—a time when iron tools and weapons were used everywhere.

Different kinds of iron were made, such as wrought iron and cast iron. These helped build bridges, railroads, and many other important things. As new ways to work with iron were found, it became cheaper and more used, changing how people lived and built their world.

Symbolic role

Iron has been important in stories and traditions. Ancient Greek poets, like Hesiod, talked about different "ages of man" named after metals such as gold, silver, bronze, and iron. This idea showed that each age brought changes to how people lived.

During the German Campaign of 1813, King Frederick William III made the first Iron Cross as a military award. People in Berlin gave their gold and silver jewellery to help pay for the war, showing how iron came to mean strength and sacrifice.

Production of metallic iron

Making iron or steel has two main steps. First, iron ore is reduced with coke inside a blast furnace to make pig iron. Pig iron has a lot of carbon. In the second step, the carbon level in pig iron is lowered to make steel, wrought iron, or cast iron. Other metals can be added to create different kinds of alloy steels.

The blast furnace is filled with iron ores like hematite or magnetite, along with coke and flux such as limestone. Hot air is blown through the mixture, causing chemical reactions that produce metallic iron. The blast furnace method creates a lot of CO₂ emissions, making it a big source of greenhouse gases globally.

Applications

Iron is one of the most used metals in the world. It is strong and cheap, which makes it great for many buildings and machines. We use iron in things like machine tools, rails, automobiles, and ship hulls. Pure iron is soft, so we mix it with other elements to make steel, which is much stronger.

Iron and steel are very important for building and making things. Different kinds of steel have different qualities, depending on what other elements are mixed in. Some steels are very hard, while others are more bendable. Iron can also be used in chemical reactions and for making colors and medicines. But iron can rust when it gets wet, so people often paint or treat it to stop it from rusting.

Biological and pathological role

Iron is very important for life. It helps make special groups called iron–sulfur clusters. These are found in enzymes that help plants change air into food. Iron is also part of proteins that carry and store oxygen in our bodies. These proteins help move oxygen from our lungs to our muscles and other parts.

In our bodies, iron is found in proteins like hemoglobin. Hemoglobin carries oxygen in our red blood cells. It is also in other proteins that help with important jobs. Most of the iron in our body is used in hemoglobin. Our bodies are good at reusing iron when we lose some. This helps keep our iron levels steady even though we only absorb a small amount each day.

Iron is found in many foods such as red meat, oysters, beans, poultry, fish, and leafy vegetables. Our bodies need iron to stay healthy. Doctors have guidelines for how much iron people should get each day depending on their age and whether they are pregnant or not. Not getting enough iron can make people feel tired and have trouble growing, especially children and women who can have babies.