Discovery and Naming
Although magnesium as an element was recognized by Scottish chemist Joseph Black in 1755, it was isolated as an impure metal in 1808 by English chemist Sir Humphry Davy [by the electrolysis of magnesium oxide (MgO) and mercuric oxide (HgO)]. The isolation of metal in the pure state was carried out in 1831 by the french chemist Antoine-Alexandre Brutus Bussy. Magnesium derives its name from “Magnesia”, a district of Greece where mineral magnesia alba was first found. It was originally known through its compounds such as Epsom salt (magnesium sulphate), magnesia or magnesia alba, and magnesite.
Sir Humphry Davy
Periodic Classification
Magnesium is a chemical element, which is classified as an Alkaline earth metal in the periodic table. It is so-called because its oxides and hydroxides are alkaline in nature, and magnesium oxides are found in the earth’s crust. It is denoted by symbol ‘Mg’ with atomic number 12. It is situated in group 2 and period 3 in the periodic table (s-block).
Properties
Magnesium is a silvery-white, lustrous, and light-weight metal. It is one of the most abundant elements in the universe and in the earth’s crust.
Magnesium Crystals
Physical Properties
Existence
It is the eighth-most abundant element in the earth’s crust, which comprises 2.1% surface by weight. It does not found in its elemental form in the earth’s crust. It occurs naturally in a combined form with elements, such as carbon, calcium, magnesium, and oxygen. Its large deposits found in minerals, such as dolomite and magnesite. The seawater also contains magnesium, which is also responsible for the hardness of the water.
Melting and Boiling Point
Its melting point is 650°C, and its boiling point is 1090°C.
Chemical Properties
Reactivity towards Air and Water
Magnesium burns with dazzling brilliance in the air to give magnesium oxide (MgO) and magnesium nitride (Mg3N2).
2Mg(s) + O2(g)→ 2MgO(s)
2Mg(s) + N2(g)→ Mg3N2(s)
It does not react with water significantly; however, a reaction takes place as follows:
Mg(s) + 2H2O(g)→ Mg(OH)2(aq) +H2(g)
Reactivity towards Halogens
Magnesium reacts with halogens (Cl2, Br2, I2) at elevated temperatures to form corresponding halides.
Mg(s) + Cl2→ MgCl2(s) (Magnesium chloride)
Mg(s) + Br2→ MgBr2(s) (Magnesium bromide)
Reactivity towards Acids
Being alkaline metal, magnesium reacts with acids to liberate dihydrogen.
Mg(s) + 2HCl(aq)→ MgCl2 + H2(g)
Magnesium Compounds
Magnesium forms many compounds, which includes its oxides, hydroxides, carbonates, chlorides and sulphates. Magnesium sulfates are readily soluble in water because hydration enthalpy of Mg2+ ions overcome the lattice enthalpy factor, and hence, it accounts for its solubility in water.
Organomagnesium Compounds (Grignard reagents)
A Grignard reagent is an organomagnesium compound, which contains a highly polar bond between carbon and magnesium. Its chemical formula is R-Mg-X where R represents alkyl or aryl group and X represents halogens. It was discovered by French chemist Victor Grignard, who won Nobel prize in chemistry for its work on these compounds. These reagents are commonly used for organic synthesis.
Grignard reagent in organic synthesis
Uses
1. Biological Role in Humans
Function
Magnesium ion is one of the most abundant ions in our body. The major roles of magnesium in biological systems are the formation of chelates with important intracellular anionic ligands, notably ATP, and it can also compete with calcium for binding sites on proteins and membranes. These are also involved in enzyme catalysed reactions (in which magnesium act as an essential cofactor) which are concerned with glycolysis, cell respiration and transmembrane transport of other cations, such as sodium and calcium. There are about 300 magnesium activated enzymes in the human body. The activity of membrane-bound Na-K-ATPase particularly depends on magnesium.
Metabolic Requirements
The average intake of magnesium for various metabolic activities is about 10-15mmol/day. The recommended daily magnesium intake for an adult is 300-400 mg (12-16mmol/day), which increases to 450 mg/day in case of pregnant, lactating ladies. Children require 150-200 mg/kg depending on age.
Magnesium-rich foods
It is widely distributed in plant and animal foods and beverages. Plant food, includes leafy vegetables, such as spinach, legumes, nuts, seeds and whole grains. Other sources of magnesium, includes tap, mineral and bottled water, but the amount of magnesium in water depends on its source and brand.
Magnesium deficiency
The low intakes or excessive losses of magnesium due to certain health conditions, chronic alcoholism and use of certain medications can lead to magnesium deficiency. Its symptoms include nausea, loss of appetite, vomiting, fatigue and weakness. Certain magnesium deficiencies also result in hypocalcemia or hypokalemia (low serum calcium or potassium levels, respectively). Its deficiency induces changes in biochemical pathways that can increase the risk of diseases and disorder, such as hypertension and cardiovascular disease, diabetes osteoporosis, and migraine headaches.
Magnesium Supplements
Magnesium supplements are available in the form of multivitamin-mineral supplements and dietary supplements. Dietary supplements are available in a variety of forms, such as magnesium oxide, citrate and chloride. Its absorption differs in different kinds of supplements. Certain studies reveal that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate.
Health Risks from Excessive Magnesium
Although too much magnesium intake does not possess any health risk because the kidneys eliminate excess amounts in the urine; however, its high doses from dietary supplements or medication often result in diarrhoea that can be followed by nausea and abdominal cramping. Excess dosages of magnesium-containing laxatives and antacids result in magnesium toxicity, including fatal hypermagnesemia.
2. Role of Magnesium in Crops
Magnesium is an essential macronutrient for the growth and development of all types of crops. It plays a key role in the photosynthesis process that helps to capture the sun’s energy for the growth and production of crops. Chlorophyll is the pigment that carries out the process of photosynthesis in plants. Magnesium is the central atom of the chlorophyll molecule. It is responsible for the green colour of leaves. It also plays an important role in activating enzymes, which are further involved in respiration and nuclear acid synthesis. It also acts as a carrier of phosphorous and is essential for phosphate metabolism and facilitates the translocation of carbohydrates and hence, enhances the production of oils and fats.
3. Magnesium Alloys
The magnesium alloys are considered as best materials for different engineering purposes due to its high strength to weight ratio, high stiffness to weight ratio, castability, machinability and excellent damping (the ability of a material to dissipate strain energy during mechanical vibration). These are the desirable properties, which are important factors in the material selection process. Due to these properties, magnesium alloys are used in various industries, such as automotive industry, aerospace industry and in hospitals.
Automotive Industry
Magnesium is the lightest of all the engineering metals, as it is 35% lighter than aluminium and over four times lighter than steel. Automotive industries always focus to manufacture lighter, environment-friendly, safer and cheaper cars. Weight reduction factor saves the energy, reduces greenhouse gas emissions and improves fuel efficiency (100 kg weight reduction of a vehicle represents a fuel saving of about 0.5 litres). Hence magnesium and its alloys are widely used in the manufacturing of various automotive parts, such as clutch and a brake pedal support brackets, steering column lock housings and manual transmission housings.
Aerospace Industry
Magnesium alloys are widely used in the aerospace industry because of their lightweight, and it exhibits good strength and stiffness at both room and elevated temperatures.
Medical Uses
Magnesium alloys are used in the manufacturing of portable medical equipment such as wheelchairs. The biocompatibility and absorbability of magnesium alloys with certain other biocompatible elements such as calcium are being evaluated for cardiovascular stunts and orthopaedic devices for internal bone fixation.
4. Pyrotechnics
Magnesium powder was used as a component of fireworks, flares and other incendiary devices (designed to cause fires). It is used to produce a brilliant white light. In photographic flashbulbs, fine magnesium wire was used, and it is used in fire starters for survival kits.
5. Epsom Salt (Magnesium Sulfate)
Magnesium sulfate (also known as Epsom salt) is the most common salt of magnesium, which is widely used as a natural remedy for a pain reliever. Its name was derived from Epsom in Surrey, England, where it was originally discovered. Epsom salt is used as bath salt, by adding it to hot baths to heal sore foot and also to reduce stress. Some people also consume it by dissolving salt to drinking water. It is believed that it cure certain ailments, such as constipation, insomnia and fibromyalgia; however, it is not scientifically proven.
