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Element Fact
There are around 120 known elements. Of these, 91 elements occur naturally on Earth. The rest no longer exist or are found only in traces as intermediate decay products alongside with other radioisotopes.

Magnesium, Mg

magnesium sample

Atomic number: 12
Atomic mass: 24.3050(6)
Natural abundance: 27640 ppm
Isotopes:
24Mg 23.985042 - 78.99%
25Mg 24.985837 - 10.00%
26Mg 25.982593 - 11.01%

History and Production

From Greek Magnesia, meaning district of Thessaly. It was first identified by J. Black in 1755 and subsequently isolated H. Davy in 1808. Is can be prepared from electrolysis of fused magnesium chloride derived from brines or sea water. It is used in flashlight photography, flares. It is also used as alloys for airplane construction and as a reducing agent in the production of titanium, uranium and other metals.

Physical Data

It is a light, silvery-white metal. It tarnishes slightly in air due to formation of the oxide film on the metal. Finely divided magnesium burns easily with a very bright white flame. Magnesium does not occur free in nature, but in the forms of carbonates, sulfates and silicates. It is an important element in both plant and animal life. For example, the Mg-porphine complexes involved in photosynthesis.

Interatomic distance: 319.8 pm
Melting point: 650C
Boiling point: 1090C
Thermal conductivity/Wm-1K-1: 156 (27C)
Density/kgm-3: 1738 (20C), 1585 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 147.1 kJ/mol
Gibbs free energy of formation: 112.5 kJ/mol
Entropy: 148.6 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Ne] 3s2
Term symbol: 1S0
Electron affinity: (not stable)   Electronegativity (Pauline): 1.31
Ionization energy (first, second, third): 737.751, 1450.69, 7732.70 kJ/mol

Chemical properties

Magnesium burns brilliantly white in air to give magnesium oxide, MgO and Mg3N2. With steam, it forms the oxide and hydrogen. In addition, magnesium also reacts with some organic compounds. For instance, with alkyl halides give Grignard reagent, an important starting reagent in synthesis of some organic compounds.

Test for magnesium:
(1) A white precipitate of magnesium ammonium phosphate, MgNH4PO4.6H2O is formed when a solution of disodium hydrogen phosphate (Na2HPO4) is added to a magnesium salt solution containing ammonium chloride and ammonia.
(2) A dyestuff p-nitrobenzene-azo-a-napthol, or 'magneson II' absorbs on magnesium hydroxide to form a blue lake. Hence, if sodium hydroxide is added to a magnesium salt solution containing the dye, a blue color is produced.


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