Магний

Описание

Magnesium is a Group 2 element (Group IIA in older labeling schemes). This element has the symbol Mg, atomic number 12, atomic weight of 24.305 g/mol and common oxidation number ＋2. It is the eighth most abundant element in the earth s crust by mass, although ninth in the Universe as a whole. This preponderance of magnesium in the Universe is related to the fact that it is easily built up in supernova stars from a sequential addition of three helium nuclei to carbon (which in turn is made from three helium nuclei). Magnesium constitutes about 2% of the Earth s crust by mass, which makes it the eighth most abundant element in the crust. Magnesium ion’s high solubility in water helps to ensure that it is the third most abundant element dissolved in seawater.

Химические свойства

Magnesium is a light, silvery-white metal in various forms, and is a fire hazard.

Физические свойства

Magnesium is a lightweight, silvery-white, malleable alkali earth metal that is flammable.It has a weak electronegativity (–1.31), which means it is highly reactive as it combines withsome nonmetals. As with other alkali earth metals, magnesium is a good conductor of heatand electricity. Its melting point is 648.8°C, its boiling point is 1090°C, and its density is1.74 g/cm³, making it about one-fifth the density of iron and only two-thirds as dense asaluminum.

Изотопы

There are 15 isotopes of magnesium, ranging from Mg-20 to Mg-34. Threeof these isotopes are stable: Mg-24 makes up 78.99% of all magnesium found in theEarth’s crust. Mg-25 makes up 10%, and Mg-26 constitutes most of the rest at 11%.The other 12 isotopes are radioactive and are produced artificially with half-lives rangingfrom microseconds to a few hours.

Происхождение имени

Magnesium is named after Magnesia, an ancient region of Thessaly, Greece, where it was mined. Magnesium is often confused with another element, manganese. One way to eliminate the confusion is to think of magnesium (Mg) as “12” and manganese (Mn) as “25” and to use the mental trick of remembering that “g” comes before “n” in the alphabet, so magnesium is the one with lower atomic number.

Вхождение

Magnesium is the eighth most abundant of the elements found in the entire universe, andthe seventh most abundant found in the Earth’s crust. Its oxide (MgO) is second in abundance to oxide of silicon (SiO₂), which is the most abundant oxide found in the Earth’s crust.Magnesium is found in great quantities in seawater and brines, which provide an endless supply. Each cubic mile of seawater contains about 12 billion pounds of magnesium. Althoughmagnesium metal cannot be extracted from seawater directly, it can be extracted by severalchemical processes through which magnesium chloride (MgCl₂) is produced. Electrolysis isthen used with the magnesium chloride as the electrolyte at 714°C to produce metallic magnesium and chlorine gas. Another method of securing magnesium is known as the Pigeonprocess. This procedure uses the magnesium minerals dolomite or ferrosilicon. Dolomite(CaCO₃), which also contains MgCO₃, is crushed and then heated to produce oxides of Caand Mg. The oxides are heated to about 1200°C along with the ferrosilicon (an alloy of ironand silicon), and the silicon reduces the magnesium, producing a vapor of metallic magnesiumthat, as it cools, condenses to pure magnesium metal.

Характеристики

While in a thin solid form, magnesium ignites at 650°C, and it is more easily ignited ina fine powder form. Burning magnesium produces a brilliant white light. It is also used asan oxidizer to displace several other metals from their compound minerals, salts, and ores. Itis alloyed with other metals to make them lighter and more machinable, so that they can berolled, pounded, formed into wires, and worked on a lathe.The ground water in many regions of the United States contains relatively high percentagesof magnesium, as well as some other minerals. A small amount improves the taste of water,but larger amounts result in “hard” water, which interferes with the chemical and physicalaction of soaps and detergents. The result is a scum-like precipitate that interferes with thecleansing action. The solution is the use of water softeners that treat hard water with eithersodium chloride or potassium chloride, which displace the magnesium—making the water“soft,” resulting in a more effective cleansing action.

Использование

magnesium plays an important role in various processes within the skin, including amino acid synthesis and protein synthesis (e.g., collagen), and in the metabolism of calcium, sodium, and phosphorus.

Определение

Metallic element of atomic number 12, group IIA of the periodic table, aw 24.305, valence = 2; three isotopes. Magnesium is the central element of the chlorophyll molecule; it is also an important component of red blood corpuscles.

Общее описание

A light silvery metal. The more finely divided material reacts with water to liberate hydrogen, a flammable gas, though this reaction is not as vigorous as that of sodium or lithium with water. In finely divided forms is easily ignited. Burns with an intense white flame. Can be wax coated to render magnesium as nonreactive.

Реакции воздуха и воды

Pyrophoric in dust form [Bretherick 1979, p. 104]. Magnesium ribbon and fine magnesium shavings can be ignited at air temperatures of about 950°F and very finely divided powder has been ignited at air temperatures below 900°F. [Magnesium Standard 1967 p. 4]. The more finely divided material reacts with water to liberate hydrogen, a flammable gas, though this reaction is not as vigorous as that of sodium or lithium

Профиль реактивности

Magnesium slowly oxidizes in moist air. Reacts very slowly with water at ordinary temperatures, less slowly at 100°C. Reacts with aqueous solutions of dilute acids with liberation of hydrogen [Merck 11th ed. 1989]. In the presence of carbon, the combination of chlorine trifluoride with aluminum, copper, lead, magnesium, silver, tin, or zinc results in a violent reaction [Mellor 2, Supp. 1. 1956]. A mixture of powdered magnesium with trichloroethylene or with carbon tetrachloride will flash or spark under heavy impact [ASESB Pot. Incid, 39. 1968]. Stannic oxide, heated with magnesium explodes [Mellor 7:401. 1946-47]. When carbon dioxide gas is passed over a mixture of powdered magnesium and sodium peroxide, the mixture exploded [Mellor 2:490. 1946-47]. Powdered magnesium plus potassium (or sodium) perchlorate is a friction- sensitive mixture [Safety Eng. Reports. 1947]. An explosion occurred during heating of a mixture of potassium chlorate and magnesium [Chem. Eng. News 14:451. 1936]. Powdered magnesium can decompose performic acid violently [Berichte 48:1139. 1915]. A mixture of finely divided magnesium and nitric acid is explosive [Pieters 1957. p. 28]. Magnesium exposed to moist fluorine or chlorine is spontaneously flammable [Mellor 4:267. 1946-47].

Опасность

Magnesium metal, particularly in the form of powder or small particles, can be ignited atrelatively low temperatures. The resulting fires are difficult to extinguish, requiring dry sandor dirt. Water will just accelerate the fire as hydrogen that will intensify the fire is releasedfrom the water.
Some magnesium compounds, whose molecules contain several atoms of oxygen—Mg(ClO₄), for example—are extremely explosive when in contact with moist organic substance,such as your hands.
Although traces of magnesium are required for good nutrition and health, some compoundsof magnesium are poisonous when ingested.

Угроза здоровью

Inhalation of magnesium dust can produceirritation of the eyes and mucous membranes.Magnesium may react with waterin the bronchial passage to form magnesiumhydroxide, which is caustic and maycause adverse effects on lungs. The fumescan cause metal fever.

Пожароопасность

Behavior in Fire: Forms dense white smoke. Flame is very bright.

Возможный контакт

Magnesium alloyed with manganese, aluminum, thorium, zinc, cerium, and zirconium, is used in aircraft, ships, automobiles, hand tools, etc., because of its lightness. Dow metal is the general name for a large group of alloys containing over 85% magnesium. Magnesium wire and ribbon are used for degassing valves in the radio industry and in various heating appliances; as a deoxidizer and desulfurizer in copper, brass, and nickel alloys; in chemical reagents; as the powder in the manufacture of flares, incendiary bombs, tracer bullets, and flashlight powders; in the nuclear energy process; and in a cement of magnesium oxide and magnesium chloride for floors. Magnesium is an essential element in human and animal nutrition and also in plants, where it is a component of altypes of chlorophyll. It is the most abundant intracellular divalent cation in both plants and animals. It is an activator of many mammalian enzymes

Канцерогенность

MgO is regarded as an “experimental tumorigen”, although the only reference in the literature that could be found relating to the carcinogenicity of MgO was an instillation study, in which MgO dust instilled intratracheally for 30 weeks resulted in induction of histiocytic lymphomas in hamsters. It was also demonstrated that MgO enhanced the tumorigenesis of benzo[a]pyrene and was an effective carrier agent for the experimental induction of respiratory tract tumors.

Экологическая судьба

Aquatic fate: Because of magnesium ion’s high solubility in water, it is the third most abundant element dissolved in seawater, because rainwater falling on rocks can also increase the level of magnesium in river and seawater.

Перевозки

UN1869 Magnesium pellets, turnings or ribbons, Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN1418 Magnesium, powder or Magnesium alloys, powder, Hazard Class: 4.3; Labels: 4.3-Dangerous when wet material, 4.2-Spontaneously combustible material. UN2950 Magnesium granules, coated, particle size not <149 μm, Hazard Class: 4.3; Labels: 4.3-Dangerous when wet material

Методы очистки

It slowly oxidises in moist air and tarnishes. If dark in colour, do not use. The shiny solid should be degreased by washing with dry Et2O, dry it in vacuo and keep it in a N2 atmosphere. It can be activated by stirring it in Et2O containing a crystal of I2 then filtering it off, before drying and storing. [Gmelin’s Magnesium (8th edn) 27A 121 1937.]

Несовместимости

Dust may form explosive mixture with air. Capable of self-ignition in moist air. The substance is a strong reducing agent. Reacts violently with, oxidizers, strong acids; acetylene, ammonium salts; arsenic, beryllium fluoride, carbon tetrachloride, carbonates, chloroform, cyanides, chlorinated hydrocarbons; ethylene oxide; hydrocarbons, metal oxides; methanol, phosphates, silver nitrate; sodium peroxide; sulfates, trichloroethylene, and many other substances, causing fire and explosion hazards. Finely divided material, in powdered, chip or sheet form, reacts with moisture or acids, evolving flammable hydrogen gas, causing fire and explosion hazard. Finely divided form is readily ignited by a spark or flame. It splatters and burns at above 1260℃