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magnesium |
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Symbol Mg. The element with atomic number 12 and relative atomic mass 24.31, which is in Group 2 of the periodic table. It is a shiny metal, which gradually dulls in air due to the formation of an oxide layer. It is a strong reductant, although its kinetic reactivity is lower than that of calcium. It reacts only slowly with cold water, but naturally reacts faster in steam. It can react directly with nitrogen, when heated strongly, as the resulting magnesium nitride has a large lattice energy due to the high charge on both the magnesium and nitride ions, and their relatively small sizes.
The ions of both magnesium and calcium are responsible for hard water. Many of magnesium\'s compounds contain the magnesium ion, Mg{TAG(tag=>sup)}2+{TAG}. Unless the anion imparts colour, magnesium compounds are white solids, such as the chloride MgCl{TAG(tag=>sub)}2{TAG} and the oxide MgO.
The small size of the atom and ion explains most of magnesium\'s differences from calcium. Its carbonate, MgCO{TAG(tag=>sub)}3{TAG}, decomposes more readily than CaCO{TAG(tag=>sub)}3{TAG} because the lattice energy of the resulting oxide, MgO, is greater. Magnesium ion\'s small size contributes to its strong bonding in one of life\'s most important molecules, chlorophyll.
Magnesium is the constructional metal with the lowest density and therefore is used where low mass is desirable, as in car wheels. However, a danger is that magnesium burns fiercely at high temperatures, so magnesium wheels can catch fire in a severe accident. This high reactivity with oxygen is used in flares. |
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