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Magnesium

Sources, Properties, Compounds, Uses

Magnesium in Periodic Table

Magnesium (Mg), chemical element, alkaline earth metal of Group 2 or IIA of the periodic table used widely in lightweight construction. It is an important mineral that controls hundreds of chemical reactions in our body for good health. Magnesium possesses a 3s2 electronic configuration over a noble gas core. This electronic configuration of the metal leads to its inclusion in Group-2 or IIA of the periodic table. Commonly, it losses s2 electrons to show a +2 oxidation state or number.

Magnesium, alkaline earth metal position on the periodic table elements

Some physical and chemical properties like melting point, boiling point, common oxidation number or state, and density given below the table.

Magnesium element chemical element and periodic table properties

Properties of Magnesium
Atomic number 12
Atomic weight 24.305
Melting point 923 K ​(650 °C, ​1202 °F)
Boiling point 1363 K ​(1091 °C, ​1994 °F)
Density 1.738 g/cm3
Molar heat capacity 24.869 J mol-1K-1
Electrical resistivity 43.9 nΩ·m
Atomic radius 160 pm
Covalent radius 141±7 pm
Chemical properties
Oxidation number +2
Electronegativity Pauling scale – 1.31
Ionization energy 1st – 737.7 kJ/mol
2nd – 1450.7 kJ/mol
3rd – 7732.7 kJ/mol

Occurrence and Production

Magnesium is a highly abundant metal that contains about 2.1 percent of the earth’s crust. It occurs principally as sedimentary rocks like dolomite (MgCO3 + CaCO3) and other evaporated forms like carnalite (KCl, MgCl2, 6H2O). A huge quantity of magnesium (0.13 percent) in sea water and the majority supply of metal now comes from the sea water. It is the eleventh most abundant element by mass in the human body which controls the biological reactions by different types of enzymes. The chlorophyll in the plants contains magnesium metal. Its compounds are widely used in medicine, antacid, and stabilizes abnormal nerve excitation or blood circulation.

Magnesium is produced either by electrolysis or silicothermal reduction. In the electrolytic method, the fused anhydrous mixture of (MgCl2 + CaCl2 + NaCl) is electrolyzed at 750°C using iron cathode and graphite anode in an inert atmosphere. In the silicothermal process or Pidgeon process, magnesium oxide or calcinated dolomite (CaO, MgO) is heated with ferrosilicon at about 1150°C in an alloy steel reactor. A high vacuum is maintained to distill out magnesium formed by the production process.

Properties and Compounds

electron distribution of magnesium atom

The hexagonal closed packed crystal lattice, magnesium is silvery-white, lustrous, and relatively soft metal. It is much harder than the alkali metals due to the presence of two electrons for chemical bonding. The ionization energy is also much than that of beryllium. This is mainly because the size of Mg+2 much higher than that of Be+2. The third ionization energy of the magnesium and other alkaline earth metals is much higher due to the closed-shell electronic configuration like the M+2 ion.

The chemistry of magnesium is marked by the small size and consequently strong electric polarization of Mg+2 ion. The chemical properties of Mg differ from the other member of the group in their behavior towards liquid ammonia. Like alkali metals, Ca, Sr, and Ba dissolve in liquid ammonia to form deep black solutions. But beryllium and magnesium do not readily dissolve in liquid ammonia.  On prolonged boiling with liquid ammonia, it evolved hydrogen to form a blue solution.

Hydride, oxide, and hydroxide

The hydride of metal was obtained by the direct combination of magnesium with hydrogen to 200 to 400°C. Hydride like CaH2, SrH2, and BaH2 is formed by ionic bonding, and BeH2 is formed by covalent bonding. Therefore, magnesium hydride has properties to form intermediate between those of ionic and covalent bond. An oxide like MgO is an ionic compound with a high melting point. The oxide reacts in water to form hydroxide. The basic properties of alkaline earth metal hydroxide increase from beryllium to barium. Beryllium hydroxide is amphoteric but all the other hydroxides are basic in nature.

Halides

Magnesium combines with halogens at a suitable temperature to form dihalide. These are also obtained by reacting the halogen hydracid with metal or its oxide. However, anhydrous magnesium halide cannot be obtained by simply heating the aqueous solution due to hydrolysis. The reaction of the halogen on a mixture of metal oxide and carbon provides the better method. Anhydrous magnesium halides dissolve in certain organic solvents like alcohol, ether, and ketone.

Organometallic Compounds

Magnesium dialkyls and diaryls may be made by the reaction of LiR or LiAr on Grignard reagent or by the reaction Mg + H2 + 2C2H4 → MgEt2 in presence of pyridine at 100°C.  Grignard reagents (MgRX) are the most widely used organometallic compounds of the metal. It is made by the slow addition of the alkyl or aryl halide to a stirred suspension of magnesium metal in ether or other solvents. It has wide applications in synthetic organic or hydrocarbon chemistry.

Uses of Magnesium

Magnesium is the third most commonly used metal after iron and aluminum and its alloys are widely used in lightweight construction like automobile and aircraft parts. Alloying is usually made with 2 to 9 percent aluminum, 1 to 3 percent of zinc, and 0.1 to 1 percent manganese. More than 3,00,000 tonnes of magnesium are produced annually over the world for the manufacture of different types of structural material. It is used as a good and useful reducing agent.

Magnesium turnings are used to reduce UF4 in graphite-lined steel reactors to produce uranium metal. It is an important mineral that controls hundreds of biological reactions for the good health of our life. Due to low density and good mechanical and electrical properties, magnesium is used for the production of mobile phones, computers (laptop and tablet), cameras, and other electronic components.