Iron

Iron, a transition metal, is the most abundant element by mass on Earth. This abundance is due to its presence in the Earth's crust, mantle, and core. It is also found in significant quantities in the sun and stars. Iron's abundance and its unique properties have made it a vital component of life on Earth and a key element in the development of human civilization.

The use of iron dates back to ancient civilizations. The Iron Age, the final epoch in human prehistory following the Stone Age and Bronze Age, was characterized (as the name suggests) by the widespread use of iron tools and weapons. This period marked a significant advancement in human technology and society, as iron tools and weapons were stronger and more durable than their bronze and stone counterparts.

Iron's durability and versatility have made it a crucial element in various industries. Iron alloys, such as steel and cast iron, are used extensively in modern industry. These alloys are stronger and more durable than pure iron, making them ideal for use in construction, transportation, and manufacturing.

Iron has 26 protons, giving it the atomic number 26. It's represented by the symbol Fe.

The most common isotope of iron possesses 30 neutrons, giving it an atomic mass of 56: iron-56. In a sample of natural iron, approximately 91% of it will be iron–56. This isotope is stable and non-radioactive, making it safe for use in a variety of applications.

The atomic structure of iron contributes to its distinct properties and uses. Iron is a silvery grey metal, which along with some other metals such as nickel, exhibits ferromagnetism. This means it can form magnets, or be attracted to magnets.

In a pure state, iron is quite reactive, and it reacts readily with water and oxygen to form iron oxide (commonly known as rust). Very finely divided metallic iron is pyrophoric, meaning it can ignite spontaneously. This reactivity is due to the presence of unpaired electrons in its outer electron shell, which eagerly react with other elements to form compounds.

Iron is a significant part of the d-block in the periodic table. The d-block, also known as the transition metals, is characterized by its elements' ability to form stable, multi-valent ions. This means it is able to form stable ions with different electrical charges. This ability is due to the presence of unpaired electrons in their outer electron shells.

Transition metals, which include iron, copper, silver, and gold, serve as a bridge between the two sides of the periodic table. They are generally hard and dense, and less reactive than alkali metals, which makes them ideal for a variety of applications.

Iron is part of group 8 in the periodic table, along with ruthenium, osmium, and hassium. These elements share similar properties due to their similar electron configurations. They all have high melting and boiling points, making them suitable for use in high-temperature applications.

Iron has been a crucial part of human civilization for over 3000 years. It is one of the metals of antiquity, seven metals which humans used in prehistoric times. The other metals of antiquity were gold, silver, copper, tin, lead, and mercury.

These metals were known to ancient civilizations and were used for a variety of purposes, from tools and weapons to jewelry and decoration. The first iron used by humans came from meteorites. Small beads of meteoric iron, shaped by hammering, have been found dating back to 3200 BCE. This suggests that humans have been using iron for at least 5000 years, and possibly even longer.

Due to its high melting point, smelted iron requires temperatures above 1,250 °C. The ability to smelt iron and the use of iron in the Iron Age led to advancements in tools, weapons, and infrastructure. This marked a significant step forward in human technology and society, as it allowed for the construction of stronger and more durable structures.

Iron is the sixth most abundant element in the universe. It is formed in the cores of dying stars during the process of stellar nucleosynthesis, where lighter elements are fused together to form heavier ones.

In the late stages of a massive star’s life, it runs out of hydrogen to fuse in its core. The helium that remains is then fused into carbon. Once the helium runs out, progressively heavier elements are created.

Once a star’s core has turned into iron, it is no longer able to burn. It collapses under its own gravity, heats up to extreme temperatures and then explodes. As stars explode, iron is scattered into space.

The formation of iron in stars contributes to the elemental diversity in the universe. This iron eventually becomes part of interstellar dust and gas clouds, which can form new stars and planets.

The Earth's core is primarily composed of iron. The inner core, in particular, is thought to be primarily composed of an iron-nickel alloy. This composition is based on seismic data and the behavior of iron under extreme pressure and temperature conditions. The inner core of the Earth is subject to pressures of nearly 3.6 million atmospheres (atm) and temperatures of around 5,200° Celsius.

Under these extreme conditions, the iron in the core exists in a solid state, despite the high temperatures. The presence of superheated, pressurized iron in the Earth's core contributes to its magnetic field. The movement of this iron generates electric currents, which in turn produce the Earth's magnetic field. This magnetic field is crucial for life on Earth, as it protects the planet from harmful solar radiation.

Every living thing on Earth, from mighty redwood trees to microscopic bacteria, needs iron to survive and grow. Even cancer cells require iron to thrive. Iron is a vital component of hemoglobin in red blood cells, which is essential for transporting oxygen throughout the body. Without sufficient iron, the body cannot produce enough healthy oxygen-carrying red blood cells, leading to iron deficiency anemia.

Symptoms of iron deficiency anemia include shortness of breath and a pale complexion. If left untreated, iron deficiency anemia can be fatal. This highlights the importance of maintaining adequate iron levels in the body.

In plants, iron is a key constituent of chlorophyll, which is critical to the process of photosynthesis. Photosynthesis is the process by which plants convert light energy into chemical energy, which is then used to fuel the plant's activities. Without iron, this process would not be possible.

Iron forms a variety of compounds, including iron oxides. Iron oxides are commonly found in nature and have a variety of uses in industry. Iron oxides are chemical compounds made of iron and oxygen. The best known is rust: a form of iron oxide that occurs when iron corrodes in the presence of water or air moisture. Other iron oxides are used as pigment, as iron ores, or as catalysts to speed up reactions.

Pigments based on iron oxides usually produce earthy oranges, reds, browns or blacks. Iron oxides can even be used as a pigment in food — food coloring based on iron oxides have the E number E172 in Europe.

A high concentration of iron oxide is responsible for the characteristic red appearance of the planet Mars. This distinctive coloring gives Mars its nickname, the 'Red Planet'. The presence of iron oxide on Mars also suggests that there may have been water on the planet in the past. Iron is the most widely used of all the metals, accounting for 90% of all metal refined today.

Its low cost and high strength make it indispensable in applications such as buildings, tools, automobiles, and in the manufacturing of steel. In manufacturing, Iron plays a crucial role, particularly in the production of steel. Steel is a mixture of iron, small amounts of carbon, and various other metals. The addition of other elements to iron changes its properties, making it more resistant to rust and corrosion.

Various types of steel have been developed to suit different purposes. Stainless steel, for example, contains chromium and other metals in addition to iron. It has a wide variety of uses including in the
manufacture of cutlery, surgical instruments, and jewelry.

Iron is used as a catalyst in the Haber process for producing ammonia and in the Fischer-Tropsch process for converting syngas (hydrogen and carbon monoxide) into liquid fuels. As a catalyst, iron speeds up these chemical reactions without being consumed in the process, making it a valuable component in these industrial processes.