Iron

Iron Element

Iron is a chemical element, the silvery-white, lustrous, malleable, and ductile metal of Group 8 (VIIIB) of the periodic table with the symbol Fe and atomic number 26. It is the most useable and cheapest metal which is used by human civilization much later than copper, silver, and gold. In learning chemistry, the chemical element iron is included in the transition metals family due to the presence of incompletely filled d-orbitals in their atomic or ionic state.

The name comes from the old English word iren while the symbol of iron comes from the Latin word Ferrum.

Physical and Chemical Properties

Physical Properties of Iron

Iron has four allotropic crystal lattices,

• α-Fe (bcc ferromagnetic)
• β-Fe (bcc paramagnetic)
• γ-Fe (fcc paramagnetic)
• δ-Fe (bcc paramagnetic)

It is the most magnetic substance among all elements and a moderately chemically active metal in the Earth’s environment.

Iron
Symbol	Fe
Discovery	approx 3500BC
Name derived from	The Anglo-Saxon name iren and symbol of iron comes from the Latin word Ferrum
Common isotope	26Fe56
Oxidation states	+6, +3, +2, 0, −2
CAS number	7439-89-6
Periodic properties
Atomic number	26
Relative atomic mass	55.845
Electron per cell	2, 8, 14, 2
Electronic Configuration	[Ar] 3d6 4s2
Block	d-block
Group	8
Period	4
Physical properties
State at 20 °C	Solid
Melting point	1538 °C, 2800 °F, 1811 K
Boiling point	2861 °C, 5182 °F, 3134 K
Molar heat capacity	25.10 J mol−1 K−1
Crystal structure	body-centered cubic (bcc) or face-centered cubic (fcc)
Density	7.87 g/cm3
Electrical resistivity	96.1 nΩ m
Atomic properties
Atomic radius (non-bonded)	2.04 Å
Covalent radius	1.24 Å
Electronegativity	1.83 (Pauling scale)
Electron affinity	14.569 kJ mol−1
Ionization energy (kJ/mol)	1st	2nd	3rd
	762.47	1561.88	2957.47

Chemical Properties of Iron

The second most abundant metal, iron has the valence electronic configuration [Ar] 3d⁶ 4s². Therefore, the common oxidation number of Fe are +2 and +3.

Iron in the Periodic Table

Iron is placed in group 8 and period 4 in the periodic table. It is a transition metal that lies between manganese and cobalt.

History of Iron

It is joined in the race of human civilization before copper, silver, and gold. It was first used by our forefathers around 4000 BC. The knowledge of extracting iron from its different types of ore developed in different countries over a long interval of time.

In Egypt and Mesopotamia, the process was discovered about 2000 BC. Early methods of heating ores with coal on windy sites yielded spongy metal shaped by prolonged hammering. The technique for making good-quality metal was developed by using a furnace.

In modern times, smelting furnaces have become well-developed. Improvement of mechanical strength by making steel from iron ores was coming in the nineteenth century.

Where is Iron Found?

Iron is the second most abundant metal after aluminum. It is the fourth most abundant chemical element after oxygen, silicon, and aluminum. It occurs to an extent of more than 5 percent or 50,000 ppm in the earth’s crust

In the earth’s crust, the free metal is rare, terrestrial iron in basaltic rocks found in Greenland. Carbonaceous sediments are found in the United States (Missouri).

About 0.5 percent of lunar soil consists of metallic iron, which means a vast quantity of Fe is present on the moon’s surface.

Ores of Iron and their Formula

The most common oxide ores and minerals that occur in the earth’s crust may include,

• red hematite (Fe₂O₃)
• brown hematite, or limonite (2F₂O₃, 3H₂O)
• magnetite (Fe₂O₃),
• siderite (FeCO₃)
• pyrites (FeS₂)

Pyrites cannot be economical to produce Fe and hence pyrites are not considered an ore of Fe.

The ores are found in different countries like China, Brazil, Australia, the United States, and India. 1000 million tonnes of iron are produced per year all over the world. The production of crude steel after 1996 over the world is around 700 million tonnes.

Isotopes

Iron occurs in nature by four stable isotopes like ⁵⁴Fe (5.845 percent), ⁵⁶Fe (91.754 percent), ⁵⁷Fe (2.119 percent), and ⁵⁸Fe (0.282 percent).

Production Process

Iron is extracted through carbon reduction in a blast furnace.

• The ore, coke, and limestone (usually ratio 8:4:1) enter the top of the furnace while a blast of preheated air at about 900 °C is brown through the holes near the bottom.
• The burning of coke produces heat near the base with a temperature near 2000 °C. It falls gradually towards the top of the furnace (400 °C).
• Burning of carbon above 700 °C produces carbon monoxide which rises upward and reduces Fe₂O₃ and FeO. Some reduction is done by carbon.
• The limestone decomposes around 900 °C to give CaO which combines with silica to form slag (CaSiO₃).

What is Pig Iron?

The molten slug and crude metal collect at the base of the blast furnace where they form separate layers. Therefore, the slug floats on molten metal, preventing it from oxidation.

These are drowned through separate holes. It is allowed to solidify in the sand mold to form pig or cast iron which contains impurities like carbon, silicon, phosphorus, sulfur, and manganese.

When most of the impurities present in pig-Fe are removed, the pure commercial form of metal is formed, known as wrought iron.

Interesting Facts about Iron

• Pure iron is chemically moderately active, silvery-white lustrous, malleable, ductile metal, and the most magnetic substance among all periodic table elements.
• The finely divided metal is pyrophoric in the air at room temperature.
• Water can react above 500 °C liberating hydrogen and forming Fe₂O₃ and FeO.
• In a heated finely divided state, it reacts with all the nonmetals (carbon, silicon, nitrogen, phosphorus, and hydrogen) to form solid metal-like compounds, Fe₃C, Fe₃Si, Fe₃P, Fe₄N, FeN, or binary ionic to covalent compounds like FeF₃, FeCl₃, FeS.
• The hard crystalline solid carbide Fe₃C (cementite) is mainly responsible for the variation of properties of steel.
• In the absence of oxygen, iron reacts with mineral acids (sulfuric acid, hydrochloric acid, or nitric acid) to give Fe (II) ions in solution.
• Dilute alkali solutions and air-free water hardly attack Fe but hot concentrated alkali hydroxides attack it.

Chemical Compounds

In chemistry, iron has characteristic properties of transition metals with various oxidation states and various types of coordination and organometallic chemical compounds in different types of chemical bonding.

+2 (ferrous) and +3 (ferric) oxidation states are the main oxidation states of Fe to form a wide number of compounds in chemistry.

In Fe (II), it forms simple compounds like oxides, halides (except iodine), and other salts, together with a large number of complex compounds. FeF₃, FeCl₃, and FeBr₃ are the halides of Fe, formed by the direct reaction of metals with respective halogens like fluorine, chlorine, and bromine.

Fe (II) is reducing in nature to form a large number of simple and complex compounds that are quite stable in +2 state. The halides, nitrate, perchlorate, and sulfate are soluble in water but the hydroxide, carbonate, phosphate, and oxalate are sparingly soluble.

It occurs in a higher oxidation state in purple potassium ferrate (KFeO₄) with a +6 oxidation state, obtained by oxidation of Fe (III) by hydrochloric acid.

What is Iron Used for?

Iron and steel are used mainly in the different types of structural units in modern civilization and civil engineering. There are different types of steel with different properties and uses, manufactured by alloyed iron with carbon and other chemical elements.

• Mild steel is most widely used in bridges, electricity pylons, bicycle chains, cutting tools, and rifle barrels.
• It is also used as a chemical catalyst in the Haber process for the production of ammonia.
• In the small-scale production of hydrogen, it is used as a reducing agent.
• Stainless steel is an important alloy of iron that contains at least 12 to 15 percent chromium and other metals such as nickel, molybdenum, titanium, and copper which resist corrosion and the action of acids. It is widely used in architecture, bearings, cutlery, medicinal surgical instruments, and jewelry.
• Cast iron is another alloy that contains 3 to 5 percent carbon, widely used in pipes, valves, pumps, and the production of magnets.

Function of Iron in the Body

It is a non-toxic essential element for all forms of life (plants and animals). A lot of iron ions is present in the hemoglobin of blood which carries oxygen from the lungs to the cell for the respiration of the body.

Deficiency of Iron

The deficiency of iron in the human body causes anemia. It is the most common neutralization disorder all over the world, in both developed and underdeveloped countries.

Chronic blood loss, repeated pregnancy, and hookworm infarction may cause anemia in the human body. Anemia is characterized by a lower concentration of iron in hemoglobin of blood (<12mg/liter), which causes retired growth, loss of appetite, sluggish metabolic activities, and dull or inactive attitude.