Magnesium is a chemical element with symbol Mg and atomic number 12. It is a shiny gray metal with low density, low melting point and high chemical reactivity. Like other alkaline earth metals (group 2 of the periodic table), it occurs naturally only with other elements and almost always has an oxidation state of +2. It readily reacts with air to form a thin magnesium oxide passivation coating that prevents further corrosion of the metal. The free metal glows with a bright-white light. The metal is mainly obtained by electrolysis of magnesium salts from brine. It is less dense than aluminum and is primarily used as a component in strong and light alloys containing aluminum.
In the universe, magnesium is formed by the successive addition of three helium nuclei to a carbon nucleus in massive, aging stars. Most of the magnesium produced by these stars is ejected into the interstellar medium during supernova explosions, where it can be recycled to form new star systems. Magnesium makes up 13% of the planet's mass and a significant part of its mantle; this makes it the eighth most abundant element in the Earth's crust and the fourth most common overall (after iron, oxygen, and silicon). It is the third most common element dissolved in seawater after sodium and chlorine.
All cells and about 300 enzymes depend on this element, which is the tenth most common element by mass in the human body. Magnesium ions interact with polyphosphate substances such as DNA, ATP and RNA. Magnesium ions are needed for thousands of enzymes to work. Magnesium compounds are used medicinally to treat disorders such as eclampsia by stabilizing abnormal neuron stimulation or blood vessel spasm, and also as antacids (such as milk of magnesia).
Elemental magnesium, a pale grayish-white metal, has a density of two-thirds that of aluminum. Among all alkaline earth metals, magnesium has the lowest melting point (923 K, 650 °C) and boiling point (1,363 K, 1,090 °C).
Magnesium in its pure polycrystalline form is brittle and quickly cracks along the cutting belts. When alloyed with small amounts of other metals such as 1 part aluminum, it becomes significantly more bendable. By reducing the grain size of polycrystalline magnesium to about 1 micron or less, it can be made significantly more malleable.
Magnesium can react with water to form hydrogen gas when finely powdered:
Mg(s) + 2H2O(g) → Mg(OH)2(aq) + H2(g) + 1203.6 kJ
This reaction is much less noticeable than the interactions of alkali metals with water, as magnesium hydroxide tends to accumulate on the surface of pure magnesium metal and stop the reaction from occurring.
Magnesium Molecular Composition
It darkens slightly when exposed to air, but unlike the heavier alkaline earth metals, magnesium does not require an oxygen-free environment for its storage as it is protected by a thin, relatively impermeable oxide coating that is difficult to remove.
Only the "normal" oxide MgO results from the direct interaction of magnesium with air or oxygen at ambient pressure. This oxide can be mixed with hydrogen peroxide to form magnesium peroxide, MgO2. It can also be treated with ozone to form peroxide, magnesium superoxide, Mg(O2)2 at low temperatures.
Although it does this much more slowly than calcium, another group 2 metal, magnesium reacts with water at ambient temperature. The metal reacts much faster when pulverized, but hydrogen bubbles slowly form on its surface when submerged in water. The reaction is faster at higher temperatures (see safety precautions). The reversible reaction between magnesium and water can be used to store energy and power a magnesium-based engine.
Similar to the exothermic reactions of HCl with aluminum, zinc, and many other metals, magnesium also reacts exothermically with most acids, including hydrochloric acid (HCl), producing metal chloride and hydrogen gas.
Günceleme: 19/01/2023 11:45