Magnesium: the essentials
Magnesium is a grayish-white, fairly tough metal. Magnesium is the eighth most abundant element in the earth's crust although not found in it's elemental form. It is a Group 2 element (Group IIA in older labelling schemes). Group 2 elements are called alkaline earth metals. Magnesium metal burns with a very bright light.
Magnesium is an important element for plant and animal life. Chlorophylls are porphyrins based upon magnesium. The adult human daily requirement of magnesium is about 0.3 g day-1.
Magnesium tarnishes slightly in air, and finely divided magnesium readily ignites upon heating in air and burns with a dazzling white flame. Normally magnesium is coated with a layer of oxide, MgO, that protects magnesium from air and water.
Magnesium: historical information
In 1618 a farmer at Epsom in England attempted to give his cows water from a well. This they refused to drink because of the water's bitter taste. However the farmer noticed that the water seemed to heal scratches and rashes. The fame of Epsom salts spread. Eventually they were recognised to be magnesium sulphate, MgSO4. Black recognized magnesium as an element in 1755. It was isolated by Davy in 1808 who electrolysed a mixture of magnesia (magnesium oxide, MgO) and mercuric oxide (HgO). Davy's first suggestion for a name was magnium but the name magnesium is now used.
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 magnesium is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Magnesium around us Read more »
Magnesium is an important element for plants and animals. Chlorophylls (responsible for the green colour of plants) are compounds knonw as porphyrins and are based upon magnesium. Magnesium is required for the proper working of some enzymes. The adult daily requirement of magnesium is about 0.3 g day-1.
Magnesium is the eighth most abundant element in the earth's crust but is never found as the free metal. There are many minerals containing magnesium including magnesite and dolomite. Sea water also contains plenty of magnesium.
|Location||ppb by weight||ppb by atoms||Links|
|Human||270000 ppb by weight||70000 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 923 [650 °C (1202 °F)] K
- Boiling point: 1363 [1090 °C (1994 °F)] K
- Enthalpy of fusion: 8.7 kJ mol-1
Crystal structure Read more »
The solid state structure of magnesium is: hcp (hexagonal close-packed).
Magnesium: orbital properties Read more »
Magnesium atoms have 12 electrons and the shell structure is 2.8.2. The ground state electronic configuration of neutral Magnesium is [Ne].3s2 and the term symbol of Magnesium is 1S0.
- Pauling electronegativity: 1.31 (Pauling units)
- First ionisation energy: 737.7 kJ mol‑1
- Second ionisation energy: 1450.7 kJ mol‑1
Isolation: magnesium can be made commercially by several processes and would not normally be made in the laboratory because of its ready availability. There are massive amounts of magnesium in seawater. This can be recovered as magnesium chloride, MgCl2 through reaction with calcium oxide, CaO.
CaO + H2O → Ca2+ + 2OH-
Mg2+ + 2OH- → Mg(OH)2
Mg(OH)2 + 2HCl → MgCl2 + 2H2O
Electrolysis of hot molten MgCl2 affords magnesium as a liquid whih is poured off and chlorine gas.
cathode: Mg2+(l) + 2e- → Mg
anode: Cl-(l) → 1/2Cl2 (g) + e-
The other methos used to produce magnesium is non electrolytic and involves dolomite, [MgCa(CO3)2], an important magnesium mineral. This is "calcined" by heating to form calcined dolomite, MgO.CaO, and this reacted with ferrosilicon alloy.
2[MgO.CaO] + FeSi → 2Mg + Ca2SiO4 + Fe
The magnesium may be distilled out from this mixture of products.
Magnesium isotopes Read more »
The Magnesium isotopes Mg-25 and Mg-26 are used to study the absorption and metabolism of Mg in the human body and they are also used for heart disease studies. Mg-25 is also used for the production of the radioisotope Na-22.
|24Mg||23.9850423 (8)||78.99 (4)||0||0|
|25Mg||24.9858374 (8)||10.00 (1)||5/2||-0.85546|
|26Mg||25.9825937 (8)||11.01 (3)||0||0|