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. Iron 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 to replace those made from copper alloys. Today, iron is used to make many everyday materials such as steel, stainless steel, and cast iron. It is a key part of our modern world.

Pure iron has a silvery-gray color. It reacts with oxygen and water to form rust. Rust flakes off and lets more iron corrode. This is why many iron objects eventually wear down. In living things, iron is very important. It helps carry oxygen in our blood through a protein called hemoglobin. It also stores oxygen in muscles with a protein called myoglobin. Our bodies need a small amount of iron from food to stay healthy.

Characteristics

Iron is a special kind of metal. It comes from the Latin word "ferrum." It has the symbol Fe and the number 26, which tells us how many tiny parts called protons are in its atoms. Iron is very common and makes up a big part of the Earth we live on.

Iron can change its shape depending on how it is treated. When it cools down from being melted, it forms different patterns of atoms. One kind, called alpha-iron, is found in ordinary conditions. Another kind, called gamma-iron, appears when iron is very hot. These changes help scientists understand what happens deep inside planets like Earth. Iron can also act like a magnet below a certain temperature, which is why some tools and toys can stick to magnets.

Origin and occurrence in nature

Iron is very common in rocky planets like Earth. It was made during big star explosions called type Ia supernovae. These explosions spread iron into space.

We find very little pure iron on Earth's surface because it changes when it meets air. But scientists think that Earth's inner and outer core are mostly made of iron mixed with nickel. The moving liquid in the outer core helps create Earth's magnetic field. Other planets like Mercury, Venus, and Mars, as well as our Moon, also likely have iron cores. Some asteroids might be made partly of iron too.

Iron is most common inside Earth, but only about 5% of the Earth's crust is made of iron. In the crust, iron mixes with other elements to make minerals such as hematite, magnetite, and siderite. These minerals are important for getting iron to use in making things. Iron is also found in rocks and can give them colors like red and yellow.

Chemistry and compounds

Iron is a special kind of metal called a transition metal. It can form many different compounds because its atoms can lose different numbers of electrons. One famous iron compound called ferrocene helped scientists learn more about these kinds of chemicals.

Iron mostly forms compounds where it has lost two or three electrons. But it can also lose up to six electrons, as in a bright purple compound called potassium ferrate (K₂FeO₄). Iron mixes well with other elements to create useful materials. For example, magnetite and Prussian blue are both important in making things like computer parts and blue coloring.

Iron does not mix with mercury, so mercury is stored in iron containers. Pure iron does not rust easily because of a protective layer that forms on its surface.

History

Main article: History of ferrous metallurgy

Iron has been known and used since ancient times. Even though iron is very common on Earth, iron objects are rarer than gold or silver because iron rusts easily. It took many years for people to learn how to make tools and weapons from iron instead of bronze.

People first used iron that fell from the sky in meteorites. These pieces of iron contained nickel and were special because they came from space. Ancient people in Egypt made beads from this kind of iron over 5,000 years ago, and a famous dagger made from meteorite iron was found in the tomb of a king named Tutankhamun. Later, people learned how to get iron from rocks, called ores, and this led to a time known as the Iron Age.

From this discovery, iron spread around the world. It was used in many places, including India, Greece, and China. During a time called the Industrial Revolution, new ways of making iron were invented, which helped build bridges, trains, and many other important things we still use today.

Symbolic role

Iron has been important in stories and traditions. Ancient Greek poets, like Hesiod, talked about different ages of humans using the names of metals. One of these was the Iron Age. This period was linked with Rome and was seen as a time when people had many challenges.

During the German Campaign of 1813, King Frederick William III made the first Iron Cross as a reward for brave soldiers. At that time, people in Berlin were asked to give their gold and silver jewellery to help pay for the war. They did this to show their support by changing precious metals into iron.

Production of metallic iron

The industrial production of iron or steel has two main steps. First, iron ore is mixed with coke in a blast furnace. This makes pig iron, which has a lot of carbon. In the second step, the carbon level is lowered to make steel or cast iron. This is done by adding or removing certain materials.

There are other ways to make iron, such as using natural gas to create a softer form of iron called sponge iron. Scientists are also studying a method called molten oxide electrolysis, which could make iron without releasing harmful gases.

Applications

Iron is one of the most commonly used metals. It makes up over 90% of all metal produced around the world. It is strong and inexpensive, which makes it perfect for building things like machine tools, rails, automobiles, ship hulls, and even the frameworks of buildings. Because pure iron is soft, it is usually mixed with other elements to create steel, which is much stronger.

Iron and its alloys have many important uses. Different types of steel are made by adding small amounts of other elements, which change the steel’s properties. Some steels are very strong but also expensive, so they are used only when needed. Iron is also used in chemistry for certain reactions and in making important materials like paints and medicines. However, iron can rust when it gets wet, so people use methods like painting or special coatings to protect it.

Biological and pathological role

Iron is very important for living things. It helps make special clusters called iron–sulfur clusters. These clusters are part of enzymes that help plants change air into useful substances. Iron is also found in proteins that carry and store oxygen in our bodies. These proteins help move oxygen from our lungs to the rest of our body.

The human body has a small amount of iron. Most of it is in a substance called hemoglobin. Hemoglobin carries oxygen in our red blood cells. Our bodies carefully manage iron levels by recycling it and controlling how much we get from food.

Iron is found in many foods such as red meat, oysters, beans, and leaf vegetables. Most people get enough iron from their food. But some people, like growing teens and women who can have babies, need more. Too little iron can cause health problems. Too much iron can also be harmful. Doctors can help figure out if someone needs more or less iron.