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.
Iron filings salts cause sparks in flames. The picture above shows the result from adding iron filings to a burning mixture of potassium chlorate and sucrose. Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment.
This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.
Iron: historical information
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.]
Iron around us Read more »
Iron compounds are essential to all life. For example, it is an iron atom in haemoglobin that is responsible for carrying oxygen around the blood stream.
Iron is not found as the free metal in nature. The most common ore is haematite (iron oxide, Fe203). Iron is found in other minerals such as magnetite, which is seen as black sands along beaches. The core of the earth, more than 2000 in radius, is composed largely of iron. The metal is the fourth most abundant element by weight in the earth's crust.
Iron is found native in meteorites known as siderites.
|Location||ppb by weight||ppb by atoms||Links|
|Human||60000 ppb by weight||6700 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 1811 [1538 °C (2800 °F)] K
- Boiling point: 3134 [2861 °C (5182 °F)] K
- Enthalpy of fusion: |203| kJ mol-1
Crystal structure Read more »
The solid state structure of iron is: bcc (body-centred cubic).
Iron: orbital properties Read more »
Iron atoms have 26 electrons and the shell structure is 18.104.22.168. The ground state electronic configuration of neutral Iron is [Ar].3d6.4s2 and the term symbol of Iron is 5D4.
- Pauling electronegativity: 1.83 (Pauling units)
- First ionisation energy: 762.5 kJ mol‑1
- Second ionisation energy: 1561.9 kJ mol‑1
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.
Iron isotopes Read more »
Iron isotopes are mainly used in nutritional studies, with Fe-57 and Fe-58 being the two most commonly used Fe isotopes. Studies have included iron-loss by human adolescents, conditions for effective iron absorption, interventions for anemia and genetic iron control. The Fe-54 isotope is used for the production of radioactive Fe-55 which in turn is used as an electron capture detector and in X-ray fluorescence. Fe-56 can be used for the production of radioactive Co-55 which is used as a tumor seeking agent in bleomycin.
|54Fe||53.9396127 (15)||5.845 (35)||0|
|56Fe||55.9349393 (16)||91.754 (36)||0|
|57Fe||56.9353958 (16)||2.119 (10)||1/2||0.09062294|
|58Fe||57.9332773 (16)||0.282 (4)||0|