Iron: the essentials

Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Iron nuclei are very stable. Iron is a vital constituent of plant and animal life, and is the key component of haemoglobin.

The pure metal is not often encountered in commerce, but is usually alloyed with carbon or other metals. The pure metal is very reactive chemically, and rapidly corrodes, especially in moist air or at elevated temperatures. Any car owner knows this. Iron metal is a silvery, lustrous metal which has important magnetic properties.

Table: basic information about and classifications of iron.

Iron: historical information

Iron was discovered by Known since ancient times at no data in not known. Origin of name: from the Anglo-Saxon word "iron" or "iren" (the origin of the symbol Fe comes from the Latin word "ferrum" meaning "iron"). Possibly the word iron is derived from earlier words meaning "holy metal" because it was used to make the swords used in the Crusades..

Iron was known in prehistoric times. Genesis says that Tubal-Cain, seven generations from Adam, was "an instructor of every artificer in brass and iron." Smelted iron artifacts have been identified from around 3000 B.C. A remarkable iron pillar, dating to about A.D. 400, remains standing today in Delhi, India. This solid pillar is wrought iron and about 7.5 m high by 40 cm in diameter. Corrosion to the pillar has been minimal despite its exposure to the weather since its erection.

Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for iron is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]

Dalton's symbol for iron

Iron: physical properties

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Iron: orbital properties

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Isolation: it is not normally necessary to make iron in the laboratory as it is available commercially. Small amounts of pure iron can be made through the purification of crude iron with carbon monoxide. The intermediate in this process is iron pentacarbonyl, Fe(CO)5. The carbonyl decomposes on heatingto about 250°C to form pure iron powder.

Fe + CO → Fe(CO)5 (250°C) → Fe + 5CO

The Fe(CO)5 is a volatile oily complex which is easily flushed from the reaction vessel leaving the impurities behind. Other routes to small samples of pure iron include the reduction of iron oxide, Fe2O3, with hyrogen, H2.

Nearly all iron produced commercially is used in the steel industry and made using a blast furnace. Most chemistry text books cover the blast furnace process. In essence, iron oxide, Fe2O3, is reduced with with carbon (as coke) although in the furnace the actual reducing agent is probably carbon monoxide, CO.

2Fe2O3 + 3C → 4Fe + 3CO2

This process is one of the most significant industrial processes in history and the origins of the modern process are traceable back to a small town called Coalbrookdale in Shropshire (England) around the year 1773.

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