# Chemistry of Magnesium (Z=12)

Magnesium is a group two element and is the eighth most common element in the earth's crust. Magnesium is light, silvery-white, and tough. Like aluminum, it forms a thin layer around itself to help prevent itself from rusting when exposed to air. Fine particles of magnesium can also catch on fire when exposed to air. Magnesium is essential in nutrition for animals and plants. It is also used as an alloy to combine with other metals to make them lighter and easier to weld, for purposes in the aerospace industry along with other industries. It is also used in medicine, in the forms of magnesium hydroxides, sulfates, chlorides, and citrates.

General Information

• Symbol: Mg
• Atomic Number: 12
• Atomic/Molar Mass: 24.31
• Melting Point: 648.8°C, 921.8K
• Boiling Point: 1090°C, 1363K
• Density:1.738 g/cc
• Oxidation states: +2
• Electron Shell Configuration: [Ne]3s2

## Characteristics

Magnesium takes it name from magnesite ore, named for the district Magnesia in Thessaly, Greece. Magnesium is a strong metal that is light and silvery-white. Recognized as a element as far back as 1775, it was first isolated in pure form by Davy in 1805. Magnesium has the ability to tarnish, which creates an oxide layer around itself to prevent it from rusting. It also has the ability to react with water at room temperature. When exposed to water, bubbles form around the metal. Increasing the temperature speeds up this reaction.

## Magnesium Fire

One property of magnesium is high flammability. Like many other things, magnesium is more flammable when it has a higher surface area to volume ratio. An example of surface area to volume ratio is seen in the lighting of fire wood. It is easier to light kindling and smaller branches than a whole log. This property of magnesium is used in war, photography, and in light bulbs. Magnesium is used in war for incendiary bombs, flares, and tracer bullets. When these weapons are used, they ignite immediately and cause fires. The only way to extinguish a magnesium fire is to cover it with sand. Water does not extinguish the fire as water reacts with the hot magnesium and releases even more hydrogen.

## Applications

Magnesium is one of the lightest metals, and when used as an alloy, it is commonly used in the automotive and aeronautical industries. The use of magnesium has increased and peaked in 1943. One reason the use of magnesium has increased is that it is useful in alloys. Alloys with magnesium are able to be welded better and are lighter, which is ideal for metals used in the production of planes and other military goods.

Another characteristic of magnesium is that it aids in the digestive process. Magnesium is commonly used in milk of magnesia and Epsom salts. These forms of magnesium can range from magnesium hydroxide, magnesium sulfate, magnesium chloride, and magnesium citrate. Magnesium not only aids in humans and animals, but also in plants. It is used to convert the sun's lights into energy for the plant in a process known as photosynthesis. The main component of this process is chlorophyll. This is a pigment molecule that is composed of magnesium. Without magnesium, photosynthesis as we know it would not be possible.

## Isotopes

Magnesium has three stable isotopes, Mg-24, Mg-25, Mg-26. The most common isotope is Mg-24, which is 79% of all Mg found on Earth. Mg25 and Mg26 are used to study the absorption and metabolism of magnesium in the human body. They are also used to study heart disease.

Magnesium not only has stable isotopes, but also has radioactive isotopes, which are isotopes that have an unstable nuclei. These isotopes are Mg--22, Mg23, Mg-27, Mg-28, and Mg-29. Mg-28 was commonly used in nuclear sites for scientific experiments from the 1950s to 1970s.

## Reactions With

Water: When exposed to steam, magnesium changes from magnesium to magnesium oxide and hydrogen.

$Mg(s) +H_2O(g) \rightarrow MgO(s) + H_2(g)$

When exposed to cold water, the reaction is a bit different. The reaction does not stop because the magnesium hydroxide gets insoluble in water.

$Mg(s) +2H_2O(g) \rightarrow Mg(OH)_2(s) + H_2(g)$

Oxygen: When exposed to oxygen, magnesium turns into magnesium oxide.

$2Mg(s) +O_2(g) \rightarrow 2MgO(s)$

Hydrogen: When exposed to hydrogen, magnesium turns into magnesium hydride.

$Mg(s) + H_2(g) \rightarrow MgH_2(s)$

Nitrogen: When reacted with nitrogen, magnesium turns into magnesium nitride.

$3Mg(s) + N_2(g) \rightarrow Mg_3N_2(s)$

Halogens: When reacted with a halogen, magnesium is very reactive. An example will be with chloride. When reacted with chloride, the product is magnesium(II) chloride.

$Mg(s) + Cl_2(g) \rightarrow MgCl_2(s)$

Acids: When reacted with acids, magnesium dissolves and forms solutions that have both the Mg(II) ion and hydrogen gas.

$Mg(s) + 2HCl(aq) \rightarrow Mg^{2+}(aq) + 2Cl^-(aq) + H_2(g)$

Bases: When reacted with bases, magnesium react.

## References

1. Avedesian, M. M., and Hugh Baker. Magnesium and Magnesium Alloys. Materials Park, OH: ASM International, 1999. Print.
2. Cowan, J. A. The Biological Chemistry of Magnesium. New York: VCH, 1995. Print.

## Problems

1. Why does magnesium not rust?
2. Why is it not possible to extinguish magnesium with water?
3. What isotopes are used for heart studies?
4. Why is magnesium commonly used to create automobiles and planes?
5. What is the common oxidation state for magnesium?

## Solutions

1. Because it is able to tarnish the ability to create a thin oxide layer around the metal.
2. Because water releases hydrogen when exposed to hot magnesium.
3. Mg25 and Mg26
4. Because it can be combined with other metals to make them lighter and easier to weld.
5. +2

## Contributors

• Ryan Kim (UC Davis)
• Avneet Kahlon (UC Davis)