Magnesium is the second element in Group 2 (IIA) of the periodic table a chart that shows how chemical elements are related to each other. The elements in Group 2 are known as the alkaline earth elements. Other elements in that group include beryllium, calcium, strontium, barium, and radium.
Compounds of magnesium have been used by humans for centuries. Yet, the element itself was not isolated until 1808. The long delay occurred because magnesium forms very stable compounds. That means that such compounds do not break down very easily.
Magnesium is the seventh most abundant element in the Earth's crust. It also occurs in large amounts dissolved in ocean waters.
Group 2 (IIA)
Alkaline earth metal
Large amounts of magnesium are used to make alloys. An alloy is made by melting or mixing two or more metals. The mixture has properties different from those of the individual metals. Magnesium alloys are quite light, yet very strong. This property makes them useful in the construction of airplanes and space-craft.
About 70 percent of the magnesium compounds produced in the United States are used in the manufacture of refractory materials. A refractory material is one that can withstand very high temperatures by reflecting heat. Refractory materials are used to line the ovens that maintain high temperatures. The remaining 30 percent of magnesium compounds are used in agriculture, construction, industrial, and chemical operations.
Discovery and naming
Compounds of magnesium are very abundant in the Earth. Dolomite, or calcium magnesium carbonate (CaMg(CO 3 2 , is an example. Dolomite has been used as a building material for centuries.
Another well-known magnesium compound is Epsom salts, or magnesium sulfate (MgSO 4 . Epsom salts are known for their soothing qualities, most notably when added to a bath. (See accompanying sidebar.)
The allure of Epsom salts
P erhaps the best know magnesium compound is magnesium sulfate (MgSO 4 ). It is popularly known as Epson salts.
One of the earliest stories about Epsom salts dates back to 1618. The town of Epsom, in Surrey, England, was suffering from a severe drought. A farmer named Henry Wicker brought his cattle to drink from a water hole on the town commons (central park). But the cattle would not drink the water. Wicker was surprised because he knew they were very thirsty. He tasted the water himself and found that it was very bitter.
The bitterness was due to magnesium sulfate in the water. This compound became known as Epsom salts.
People soon learned that soaking in the natural waters that contained Epsom salts made them feel better. The salts seemed to have properties that soothed the body. Before long, soaking in these waters became very popular.
Today, Epsom salts are used in bath water. They relax sore muscles and remove rough skin. Many people believe the salts have the same relaxing effect as hot springs. Some gardeners even believe that sprinkling Epsom salts in the garden helps flowers and vegetables grow!
Careful studies of magnesium and its compounds began in the middle 1700s. Scottish physician and chemist Joseph Black (1728-99) carried out some of the earliest experiments on magnesium compounds. He reported on his research in an article that became famous. Black is sometimes given credit for "discovering" magnesium because of his work with the element.
By 1800, chemists knew that magnesium was an element. But no one had been able to prepare pure magnesium metal. Magnesium holds very tightly to other elements in its compounds. No one had found a way to break the bonds between magnesium and these other elements.
In 1808, English chemist Humphry Davy (1778-1829) solved the problem by
passing an electric current through molten (melted) magnesium oxide (MgO).
The current caused the compound to break apart, forming magnesium metal
Davy used this method to discover a number of other elements. (See sidebar on Davy in the calcium entry in Volume 1.) Like magnesium, these elements form compounds that are very difficult to break apart. An electric current provides the energy to break these compounds down into their elements.
The name magnesium goes back many centuries. It was selected in honor of a region in Greece known as Magnesia. The region contains large supplies of magnesium compounds.
Magnesium is a moderately hard, silvery-white metal. It is the lightest of all structural metals. These metals are strong enough to be used to build buildings, bridges, automobiles, and airplanes.
Magnesium is easily fabricated. Fabrication means shaping, molding, bending, cutting, and working with a metal. Metals must be fabricated before they can be turned into useful products. Metals that are strong, tough, or hard are not easily fabricated. They must be converted to an alloy. A metal that is more easily fabricated (such as magnesium) is combined with them.
The melting point of magnesium is 651°C (1,200°F) and its boiling point is 1,100°C (2,000°F). Its density is 1.738 grams per cubic centimeter.
Magnesium is a fairly active metal. It reacts slowly with cold water and more rapidly with hot water. It combines with oxygen at room temperature to form a thin skin of magnesium oxide. It burns with a blinding white light at higher temperatures. Magnesium reacts with most acids and with some alkalis. An alkali is a chemical with properties opposite those of an acid. Sodium hydroxide (common lye such as Drano) and lime-water are examples of alkalis.
Magnesium also combines easily with many non-metals, including nitrogen, sulfur, phosphorus, chlorine, fluorine, bromine, and iodine. It also reacts readily with a number of compounds, such as carbon monoxide (CO), carbon dioxide (CO 2 , sulfur dioxide (SO 2 , and nitric oxide (NO).
Occurrence in nature
The abundance of magnesium in the Earth's crust is estimated to be about 2.1 percent. That makes it the sixth most common element in the earth. It also occurs in seawater. A cubic mile of seawater is estimated to contain up to six million tons of magnesium.
There are many naturally occurring minerals of magnesium. Some of the most important are dolomite; magnesite, or magnesium carbonate (MgCO 3 ; carnallite, or potassium magnesium chloride (KMgCl 3 ; and epsomite, or magnesium sulfate (MgSO 4 .
The largest producer of magnesium ores is Turkey. Other large producers are North Korea, China, Slovakia, Austria, and Russia. The amount of magnesium produced in the United States is not reported in order to protect trade secrets.
Magnesium produced in the United States comes from three sources: seawater, brine, and mines. Seawater is processed to obtain magnesium by companies in California, Delaware, Florida, and Texas. Magnesium is obtained from brine in Michigan and Utah. Brine is water that is even saltier than seawater. Finally, some magnesium compounds are taken from mines in Nevada, North Carolina, and Washington.
There are three naturally occurring isotopes of magnesium: magnesium-24, magnesium-25, and magnesium-26. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
One radioactive isotope of magnesium, magnesium-28, also exists. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive. Magnesium-28 has no important commercial uses.
Magnesium is prepared by one of two methods. The first method is similar to the method used by Davy in 1808. An electric current is passed through molten (melted) magnesium chloride:
The second method involves reacting magnesium oxide with ferrosilicon. Ferrosilicon is an alloy of iron and silicon. When magnesium oxide and ferrosilicon react, free magnesium metal is formed.
Although most cameras now use electronic flashes, magnesium metal is often contained in cameras that use flash bulbs. A thin strip of magnesium metal is inside the bulb. When the
A common use of magnesium metal is in fireworks. Most firework displays include some brilliant flashes of very white light. Those flashes are produced by the burning of magnesium metal.
Magnesium is commonly alloyed with other metals. Magnesium and aluminum, for instance, are two metals that combine to form alloys that are very strong and resistant to corrosion (rust). But they weigh much less than steel alloys with similar properties.
Strength and low density are important properties in the manufacture of airplanes, automobiles, metal luggage, ladders, shovels and other gardening equipment, racing bikes, skis, race cars, cameras, and power tools. A typical magnesium alloy contains about 90 percent magnesium, 2 to 9 percent aluminum, and small amounts of zinc and manganese.
The largest single use of magnesium compounds is in refractories. Other magnesium compounds are used in the following categories:
medicine: pain killer and fever reducer (magnesium acetylsalicylate); antacid to neutralize stomach acid (magnesium hydroxide; magnesium phosphate; magnesium silicate); laxative to loosen the bowels (magnesium carbonate; magnesium chloride; magnesium citrate; magnesium hydroxide; magnesium lactate; magnesium phosphate); antiseptic to kill germs (magnesium borate; magnesium salicylate; magnesium sulfate); sedative to help one get sleep (magnesium bromide)
production of glass and ceramics: magnesium fluoride; magnesium oxide
mothproofing of textiles: magnesium hexafluorosilicate
fireproofing wood for construction: magnesium phosphate
manufacture of paper: magnesium sulfite
Magnesium is essential for good health in both plants and animals. It forms part of the chlorophyll molecule found in all green plants. Chlorophyll is the molecule in green plants that controls the conversion of carbon dioxide and water to carbohydrates, such as starch and sugar. Plants that do not get enough magnesium cannot make enough chlorophyll. Their leaves develop yellowish blotches as a result.
Magnesium is found in many enzymes in both plants and animals. An enzyme is a catalyst in a living organism. It speeds up the rate at which certain changes take place in the body. Enzymes are essential in order for living cells to function properly. It is difficult not to get enough magnesium in one's daily diet. It is found in nuts, cereals, seafoods, and green vegetables. Most people have no problem getting the 300 to 400 milligrams of magnesium recommended in the daily diet.
Magnesium forms part of the chlorophyll molecule found in all green plants.
A lack of magnesium can occur, however. For example, alcoholics and children in poor countries sometimes develop a magnesium deficiency. In such cases, magnesium deficiency may cause a person to become easily upset or overly aggressive.
On the other hand, it is also possible to be exposed to too much magnesium. For example, inhaling magnesium powder can produce irritation of the throat and eyes, resulting in a fever. In large doses, magnesium can cause damage to muscles and nerves. It can eventually result in loss of feeling and paralysis (inability to move parts of the body).
Such conditions are rare. They are likely to occur only among people who have to work with magnesium metal on a regular basis.