MAGNESIUM

Physical Properties

Atomic Number: 12
Mass Number: 24.305
Electron Configuration: 1s²2s²2p⁶3s²
Crystal Structure: Hexagonal Close-Packed
Density: 1.74 g/cm³
Melting Point: 649^oC
First Ionization Energy: 737.1 kJ/mol
Second Ionization Energy: 1451 kJ/mol
Atomic Radius: 160 pm
Ionic Radius: 66 pm

Magnesium is the second lightest member of the alkaline earth metals. It is sometimes combined with aluminum to form a lightweight alloy. Magnesium forms a wide range of ionic compounds. Some common magnesium compounds include milk of magnesia, which is a suspension of magnesium hydroxide and epson salts, which is magnesium sulfate hepahydrate. The ionic compounds of magnesium generally tend to be more soluble than the heavier members of the group. Magnesium can also form covalent bonds with carbon, an example of which is the Grignard reagent phenylmagnesium bromide. Chlorophyll, the compound responsible for the green color of leaves and for photosynthesis, is a coordination compound containing magnesium.

The most important sources of magnesium are seawater and dolomite rock, a mixture of calcium and magnesium carbonates. Magnesium is generally obtained by the electrolysis of magnesium halides. In the production of magnesium from seawater the magnesium is precipitated as the hydroxide and converted to the chloride by reaction with hydrochloric acid. The magnesium chloride is reccovered by evaporation of the solution, and magnesium metal is obtained by electrolysis of the molten salt.

Magnesium is one of the least reactive of the alkaline earth metals. If heated it wil react with water to form magnesium hydroxide and hydrogen gas, but this reaction occurs very slowly. Magnesium ribbon burns in air with a brilliant white light to form magnesium oxide. In fact, old-fashioned flash bulbs contained magnesium wire in an atmosphere of pure oxygen. Magnesium will also react with any of the halogens to form the corresponding magnesium halide, and will react with nitrogen to form magnesium nitride at high temperatures. When heated with sulfur, magnesium sulfide is formed. Magnesium reacts readily with acids and displaces the hydrogen from the acid as hydrogen gas.

Burning Magnesium. A strip of magnesium metal burns with a brilliant white light when ignited. The light is very bright and should not be viewed with the naked eye.