Iron
Like other group 8 elements, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike many other metals which form passivating oxide layers, iron oxides occupy more volume than iron metal, and thus iron oxides flake off and expose fresh surfaces for corrosion.
Iron metal has been used since ancient times, though copper alloys, which have lower melting temperatures, were used first in history. Pure iron is soft (softer than aluminium), but is unobtainable by smelting. The material is significantly hardened and strengthened by impurities from the smelting process, such as carbon. A certain proportion of carbon (between 0.002% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, which has a high carbon content. Further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and low carbon iron alloys with other metals (alloy steels) are by far the most common metals in industrial use, due to their great range of desirable properties and the abundance of iron.
Iron chemical compounds, which include ferrous and ferric compounds, have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. It forms binary compounds with the halogens and the chalcogens. Among its organometallic compounds is ferrocene, the first sandwich compound discovered.
Iron plays an important role in biology, forming complexes with molecular oxygen in hemoglobin and myoglobin; these two compounds are common oxygen transport proteins in vertebrates. Iron is also the metal used at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals.
Occurrence
Planetary occurrence
Iron is the sixth most abundant element in the Universe, and the most common refractory element. It is formed as the final exothermic stage of stellar nucleosynthesis, by silicon fusion in massive stars.
Metallic or native iron is rarely found on the surface of the Earth because it tends to oxidize, but its oxides are pervasive and represent the primary ores. While it makes up about 5% of the Earth's crust, both the Earth's inner and outer core are believed to consist largely of an iron-nickel alloy constituting 35% of the mass of the Earth as a whole. Iron is consequently the most abundant element on Earth, but only the fourth most abundant element in the Earth's crust. Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite and magnetite. Large deposits of iron are found in banded iron formations. These geological formations are a type of rock consisting of repeated thin layers of iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shale and chert. The banded iron formations were laid down in the time between 3,700 million years ago and 1,800 million years ago
About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). Although rare, iron meteorites are the main form of natural metallic iron on the Earth's surface. It was proven by Mössbauer spectroscopy that the red color of the surface of Mars is derived from an iron oxide-rich regolith.
| Symbol | Fe | |
| Atomic Number | 26 | |
| Atomic Weight | 55.847 | |
| Oxidation States | +2,+3 | |
| Electronegativity, Pauling | 1.83 | |
| State at RT | Solid, Metal | |
| Melting Point, K | 1808 | |
| Boiling Point, K | 3023 |
Interesting Facts about Iron
- One third of Earth’s mass is believed to be iron, most of which lies deep within the planet, in the core.
- There is enough iron on Earth to make three new planets, each with the same mass as Mars.
- Circulation of liquid iron deep in the earth is believed to create the electric currents that create our planet’s magnetic field.
- Iron is essential for human brain development. Iron deficiency in children leads to, among other problems, an impaired ability to learn.
- In ancient times, people did not know how very abundant iron was on Earth. Their only source of metallic iron was meteorites. From Assyrian writings we learn that iron was eight times more valuable than gold. In addition to its rarity, iron may also have been very desirable because, coming from the sky, it was thought to be a gift from the gods: the ancient Egyptians called it ‘ba-ne-pe’, meaning ‘metal of heaven.’ The connection with heaven is reinforced by Pyramid Texts which translate, for example, to: ‘my bones are iron and my limbs are the imperishable stars.’
- Iron was the first magnetic metal discovered. Lodestones were used by ancient navigators because they could be used as compasses, pointing to the magnetic north pole; this was described by the ancient Greek philosopher Thales of Miletus in 600 BC. Lodestones were made from magnetite, which is a naturally occurring oxide of iron. Magnetite’s formula is FeO.Fe2O3.
- Some animals have a sixth sense – the magnetic sense. Magnetite has been found in a wide range of animals, including honey bees, homing pigeons, and dolphins. These animals are sensitive to the earth’s magnetic field, helping their ability to navigate.
- The Hoba meteorite in Namibia is the largest naturally occurring piece of iron in the world, weighing in at over 60 tons. It’s made of 82 – 83% iron, 16 – 17 % nickel, about 1% cobalt, and very small traces of other elements. The Hoba meteorite is the largest single meteorite ever found.
- Iron is ferromagnetic. Ferromagnetism is the strongest type of magnetism. Other common ferromagnetic metals are nickel and cobalt.
- Very powerful magnets can be made using iron, nickel or cobalt in association with rare earth metals. NIB magnets (Neodymium – Iron – Boron) were invented in the early 1980s. They are an alloy in the proportions Nd2Fe14B. They are used in computers, cell phones, medical equipment, toys, motors, wind turbines and audio systems.
Appearance and Characteristics
Harmful effects:
Iron is considered to be non-toxic.
Characteristics:
- Iron is a ductile, gray, relatively soft metal and is a moderately good conductor of heat and electricity.
- It is attracted by magnets and can be readily magnetized.
- The pure metal is chemically very reactive and rusts readily in moist air, forming red-brown oxides.
- There are three allotropic forms of iron, known as alpha, gamma, and delta.
- Alpha iron, also known as ferrite, is the stable form of iron at normal temperatures.
Uses of Iron
- Iron is the cheapest and most important of all metals – important in the sense that iron is overwhelmingly the most commonly used metal, accounting for 95 percent of worldwide metal production.
- Iron is used to manufacture steel and other alloys important in construction and manufacturing.
- Iron is also vital in the functioning of living organisms, transporting oxygen in blood via the hemoglobin molecule.
Iron burned in pure oxygen to form iron oxide.
Now, in the reverse of the first video, iron oxide is reduced back to iron.
