Iron

26

Fe

55.85

Red blood cells - the color comes from iron in hemoglobin. The cells are magnified x 10 000. If you grew x 10 000, you could place your feet in Seattle and touch Perth, Australia with your hands. Iron in hemoglobin carries oxgyen around our bodies. Image: CDC.

Classification:	Iron is a transition metal
Atomic weight:	55.847 g/mol
Density @ 20 ^oC:	7.87 g/cm³
Atomic volume:	7.1 cm³/mol

Close up of an iron meteorite: Meteorites such as this one were probably our ancestors' first source of iron. This is a fragment of the Sikhote-Alin meteorite - approximately 93% iron, 6% nickel and 1% other elements. The meteorite surface has been melted into thumb-print shapes during its flight through our atmosphere. Photo by Carl Allen, NASA JSC Photo S94-43472

Scrap iron and steel for recycling. How times have changed. Iron was once worth eight times more than gold.

Discovery of Iron

Author: Dr. Doug Stewart

Iron has been known since ancient times.

The first iron used by humans is likely to have come from fallen meteorites. Most objects that fall to earth from space are stony, but a small proportion, such as the one pictured right are 'iron meteorites' with iron contents of over 90 percent.

Iron corrodes easily, so iron artifacts from ancient times are much rarer that objects made of silver or gold. This makes it harder to trace the history of iron than the less reactive metals.

Artifacts made from meteorite iron have been found dating from about 5000 BC (and so are about 7000 years old) - for example iron beads in graves in Egypt. ⁽¹⁾

In Mesopotamia (Iraq) there is evidence people were smelting iron around 5000 BC. Artifacts made of smelted iron have been found dating from about 3000 BC in Egypt and Mesopotamia. ^{(1), (2), (3)}

In those times, iron was a ceremonial metal; it was too expensive to be used in everyday life. Assyrian writings tell us that iron was eight times more valuable than gold. ⁽¹⁾

The iron age began about 1300-1200 BC when iron became cheap enough to replace bronze.

Adding carbon to iron to make steel was probably accidental at first - a coming together of molten iron and charcoal from the smelting fire. This probaby happened about 1000 BC. ⁽⁴⁾

Until this happened there were few technological reasons for the bronze age to give way to the iron age; the techniques of improving iron by adding carbon (to make steel) and coldworking were needed before iron would be wholly preferred to bronze. ⁽⁵⁾

Iron was used commonly in Roman times. In the first century Pliny the Elder said, "It is by the aid of iron that we construct houses, cleave rocks, and perform so many other useful offices in life." ⁽⁶⁾

The origin of the chemical symbol Fe is from the Latin word 'ferrum,' meaning iron. The word iron itself comes from 'iren' in Anglo-Saxon.

State (s, l, g): solid
Melting point: 1808.2 K (1535.1 ^oC)

Boiling point: 3023 K (2750 ^oC)

Specific heat capacity: 0.44 J g^-1 K^-1
Heat of fusion: 13.80 kJ mol^-1
1^st ionization energy: 759.3 kJ mol^-1
3^rd ionization energy: 2957.3 kJ mol^-1

Heat of atomization: 415 kJ mol^-1
Heat of vaporization: 349.60 kJ mol^-1
2^nd ionization energy: 1561.1 kJ mol^-1
Electron affinity: 15.7 kJ mol^-1

Shells: 2,8,14,2
Minimum oxidation number: -2
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 1.9

Electron configuration: [Ar] 3d⁶ 4s²
Maximum oxidation number: 6
Max. common oxidation no.: 3
Polarizability volume: 8.4 Å³

Structure: bcc: body-centered cubic
Hardness: 4.0 mohs

Iron burned in pure oxygen to form iron oxide.

Now, in the reverse of the first video, iron oxide is reduced back to iron.

Color: gray

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:
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.

Reaction with air: mild, ⇒ Fe₃O₄
Reaction with 3 M HNO₃: passivated
Oxide(s): FeO, Fe₂O₃ (hematite), Fe₃O₄ (magnetite),
Hydride(s): none

Reaction with 6 M HCl: vigorous, ⇒ H₂, FeCl₂
Reaction with 6 M NaOH:
Chloride(s): FeCl₂, FeCl₃

Atomic radius: 140 pm
Ionic radius (2+ ion): 77 pm
Ionic radius (2- ion): pm

Ionic radius (1+ ion): pm
Ionic radius (3+ ion): 63 pm
Ionic radius (1- ion): pm

Thermal conductivity: 80.4 W m^-1 K^-1

Electrical conductivity: 0.112 x 10⁶ S cm^-1

Abundance earth's crust: 5.6 % weight, 2.1 % by moles
Abundance solar system: 1000 parts per million by weight, 30 parts per million by moles
Cost, pure: $7.2 per 100g
Cost, bulk: $0.02 per 100g

Source: Iron is not found free in nature but is found in iron ores such as hematite (Fe₂O₃), magnetite (Fe₃O₄) and taconite. Commercially, iron is produced in a furnace at temperatures of about 2000 ^oC by the reduction of hematite or magnetite with carbon.

Isotopes: Iron has 24 isotopes whose half-lives are known, with mass numbers 46 to 69. Of these, four are stable, ⁵⁴Fe, ⁵⁶Fe, ⁵⁷Fe and ⁵⁸Fe. Over 91.7% of of naturally occurring iron is in the form of ⁵⁶Fe.

1. Henry Maryon, Early Near Eastern Steel Swords., 65, 1961, American Journal of Archaeology p1.
2. Michael D. Fenton, Mineral Commodity Profiles - Iron and Steel., 2005, U.S. Geological Survey.
3. R. J. Forbes, Studies in Ancient Technology., IX, 1965, p247.
4. Michael Woods, Mary B. Woods, Ancient Machines: From Wedges to Waterwheels., 2000, p30, Runestone Press.
5. Vincent C. Pigott, The Archaeometallurgy of the Asian Old World, 1999, p28, UPenn Museum of Archaeology.
6. Mary Elvira Weeks, Discovery of the Elements., 2003, p5, Kessinger Publishing.

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Iron Element Facts

Discovery of Iron

States

Energies

Oxidation & Electrons

Appearance & Characteristics

Reactions & Compounds

Radius

Conductivity

Abundance & Isotopes

References

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