Metallic magnesium finds applications in lightweight alloys and in high-temperature combustion reactions. Not to be confused, magnesium ions play important roles in hundreds of biological enzymes.
Magnesium represents an interesting study in how properties of a neutral metal may be considerably different from properties of ionic – positively or negatively charged – magnesium compounds.
Magnesium ions and their compounds are extremely important in biological systems. Magnesium is a vital nutrient found in the cells of all living things, and leafy green vegetables are an especially good source of this nutrient. Magnesium plays a vital role in muscle contraction – people who do not have enough magnesium in their diets often experience muscle cramps. Magnesium is also important in the production and transport of energy within the human body, and it supports healthy function of many enzymes, such as those that synthesize DNA and RNA.
Metallic magnesium, because of its high reactivity, is virtually never found uncombined in nature. If magnesium metal is isolated, however, it rapidly acquires a coating of magnesium oxide, which protects it from reaction. In bulk, magnesium is difficult to ignite, but when powdered or reduced to thin strips, magnesium is extremely flammable. During World War II, magnesium was used in incendiary devices and bombs, and the only effective way to put out those fires was to smother them with dry sand.
More benignly, magnesium’s brilliant, white flame has played an important aesthetic role. Magnesium powder was used in the late 1800’s and early 1900s as flash powder for photography. Magnesium is also used for fireworks, and its high temperature combustion may be used to ignite other reactions such as thermite.
Because magnesium metal is less dense than aluminum, it is also highly prized to make lightweight alloys. Porsche and Mercedes-Benz have both used magnesium for the construction of champion lightweight racecars. Concerns over the flammability of magnesium have generally minimized its use in airplanes, but interest has been growing with the increasing desire for lightweight aircraft resulting in better fuel efficiencies.
The vast difference between the properties and uses of ionic magnesium salts and neutral magnesium is one of the wonders of chemistry.