| References | Mercury, also called quicksilver, is a chemical element in the periodic table that has the symbol Hg (Latinized Greek: hydrargyrum, meaning watery or liquid silver) and atomic number 80. A heavy, silvery transition metal, mercury is one of five elements that are liquid at or near room temperature and pressure.[1] The others are the metals caesium, francium, and gallium, and the non-metal bromine.
Mercury is used in thermometers, barometers and other scientific apparatus, though concerns about the element's toxicity have led to mercury thermometers being largely phased out in clinical environments in favour of alcohol-filled, digital, or thermistor-based instruments. It remains in use in a number of other ways in scientific and scientific research applications, and in dental amalgam. Mercury is mostly obtained by reduction from the mineral cinnabar. Mercury occurs in deposits throughout the world and it is harmless in an insoluble form, such as mercuric sulfide, but it is poisonous in soluble forms such as mercuric chloride or methylmercury. |
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| History | Mercury was known to the ancient Chinese and Hindus, and was found in Egyptian tombs that date from 1500 BC.[citation needed] In China, India, and Tibet, mercury use was thought to prolong life, heal fractures, and maintain generally good health. China's first emperor, Qin Shi Huang Di - said to have been buried in a tomb that contained rivers of flowing mercury, representative of the rivers of China - was driven insane and killed by mercury pills intended to give him eternal life.[citation needed] The ancient Greeks used mercury in ointments and the Romans used it in cosmetics. By 500 BC mercury was used to make amalgams with other metals. The Indian word for alchemy is Rasavatam which means "the way of mercury".
Alchemists often thought of mercury as the First Matter from which all metals were formed. They believed that different metals could be produced by varying the quality and quantity of sulfur contained within the mercury. The purest of these was gold, and mercury was required for the transmutation of base (or impure) metals into gold as was the goal of many alchemists. Hg is the modern chemical symbol for mercury. It comes from hydrargyrum, a Latinized form of the Greek word (hydrargyros), which is a compound word meaning "water" and "silver" — since it is liquid, like water, and yet has a silvery metallic sheen. The element was named after the Roman god Mercury, known for speed and mobility. It is associated with the planet Mercury. The astrological symbol for the planet is also one of the alchemical symbols for the metal. Mercury is the only metal for which the alchemical planetary name became the common name. |
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| Occurrence | Mercury is an extremely rare element in the earth's crust, having an average crustal abundance by mass of only 0.08 parts per million. However, because it does not blend geochemically with those elements that constitute the majority of the crustal mass, mercury ores can be extraordinarily concentrated considering the element's abundance in ordinary rock. The richest mercury ores contain up to 2.5% mercury by mass, and even the leanest concentrated deposits are at least 0.1% mercury (12,000 times average crustal abundance).
It is found either as a native metal (rare) or in cinnabar, corderoite, livingstonite and other minerals, with cinnabar (HgS) being the most common ore. Mercury ores usually occur in very young orogenic belts where rock of high density are forced to the crust of the Earth, often in hot springs or other volcanic regions. Over 100,000 tons of mercury was were mined from the region of Huancavelica, Peru, over the course of three centuries following the discovery of deposits there in 1563; mercury from Huancavelica was crucial in the production of silver in colonial Spanish America. Many former ores in Italy, Slovenia, the United States and Mexico which once produced a large proportion of the world's supply have now been completely mined out. The metal is extracted by heating cinnabar in a current of air and condensing the vapor. In 2005, China was the top producer of mercury with almost two-thirds global share followed by Kyrgyzstan, reports the British Geological Survey.[citation needed] Several other countries are believed to have unrecorded production of mercury from copper electrowinning processes and by recovery from effluents. Due to minimal surface disruption, mercury mines lend themselves to constructive re-use. For example, in 1976 Santa Clara County, California purchased the historic Almaden Quicksilver Mine and proceeded to create a county park on the site, after conducting extensive safety and environmental analysis of the property. |
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| Applications | Mercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic applications. It is used in some thermometers, especially ones which are used to measure high temperatures (In the United States, non-prescription sale of mercury fever thermometers is banned by a number of different states and localities). Other uses:
Mercury was used inside wobbler (fishing) lures. Its heavy, liquid form made it useful since the lures made an attractive irregular movement when the mercury moved inside the plug. Such use was stopped due to environmental concerns, but illegal preparation of modern fishing plugs has occurred. Mercury sphygmomanometers. Mercury barometers, diffusion pumps, coulometers, and many other laboratory instruments. As an opaque liquid with a high density and a nearly linear thermal expansion, it is ideal for this role. The triple point of mercury, -38.8344 °C, is a fixed point used as a temperature standard for the International Temperature Scale (ITS-90). In some gaseous electron tubes, mercury arc rectifier Gaseous mercury is used in mercury-vapour lamps and some "neon sign" type advertising signs and fluorescent lamps. Liquid mercury was sometimes used as a coolant for nuclear reactors; however, sodium is proposed for reactors cooled with liquid metal, because the high density of mercury requires much more energy to circulate as coolant. Liquid mercury has been proposed as a working fluid for a heat pipe type of cooling device for spacecraft heat rejection systems or radiation panels. Mercury was a propellant for early ion engines in electric propulsion systems. Advantages were mercury's high molecular weight, low ionization energy, low dual-ionization energy, high liquid density and liquid storability at room temperature. Disadvantages were concerns regarding environmental impact associated with ground testing and concerns about eventual cooling and condensation of some of the propellant on the spacecraft in long-duration operations. The first spaceflight to use electric propulsion was a mercury-fueled ion thruster SERT-1 launched by NASA at NASA's Wallops Flight Facility in 1964. SERT stands for Space Electric Rocket Test. The SERT-1 flight was followed up by the SERT-2 flight in 1970. Mercury and Cesium were preferred propellants for ion engines until Hughes Research Laboratory performed studies finding Xenon gas to be suitable replacement. Xenon is now the preferred propellant for ion engines as it has a high molecular weight, little or no reactivity due its noble gas nature, and has a high liquid density under mild cryogenic storage. Experimental Mercury vapour turbines were proposed to increase the efficiency of fossil-fuel electrical power plants. Mercury was once used in the amalgamation process of refining gold and silver ores. This polluting practice is still used by the garimpeiros (gold miners) of the Amazon basin in Brasil and by illegal miners in South Africa. Mercury is still used in some cultures for folk medicine and ceremonial purposes which may involve ingestion, injection, or the sprinkling of elemental mercury around the home. It must be emphasized that the former two procedures, especially, are extremely hazardous and the latter is nearly as so because mercury spreads easily and is therefore ingested. Alexander Calder built a mercury fountain for the Spanish Pavilion at the 1937 World's Fair in Paris. The fountain is now on display at the Fundació Joan Miró in Barcelona. Used in electrochemistry as part of a secondary reference electrode called the calomel electrode as an alternative to the Standard Hydrogen Electrode. This is used to work out the electrode potential of half cells. Used in Cold Cathode (also generalised under the Neon Sign Industry) lighting to increase the success of ionization and conductivity in Argon filled lamps, an Argon filled lamp without Mercury will have dull spots and will fail to light correctly. Lighting containing Mercury can only be bombarded/oven pumped once. When added to Neon filled tubes the light produced will be inconsistent red/blue spots until the initial burning-in process is completed; eventually it will light a consistent dull off-blue colour. Mercury was once used as a gun barrel bore cleaner. |
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| Isotopes | There are seven stable isotopes of mercury with Hg-202 being the most abundant (29.86%). The longest-lived radioisotopes are 194Hg with a half-life of 444 years, and 203Hg with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day. 199Hg and 201Hg are the most often studied NMR-active nuclei, having spins of 1/2 and 3/2 respectively. | ||||||
| Reactivity | Mercury dissolves to form amalgams with gold, zinc and many metals. Because iron is an exception to this rule, iron flasks have been traditionally used to trade mercury. When heated, mercury also reacts with oxygen in air to form mercury oxide, which then can be decomposed by further heating to higher temperatures.
Since it is below hydrogen in the reactivity series of metals, mercury does not react with most acids, such as dilute sulfuric acid, though oxidizing acids such as concentrated sulfuric acid and nitric acid or aqua regia dissolve it to give sulfate and nitrate and chloride. Similar to silver, mercury reacts with atmospheric hydrogen sulfide. Mercury even reacts with solid sulfur flakes, which is used in mercury spill kits to absorb mercury vapors (spill kits also use activated charcoal and powdered zinc). |
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| Compounds | The most important salts are
Mercury(I) chloride (AKA calomel) is sometimes still used in medicine and acousto-optical filters; Mercury(II) chloride (which is very corrosive, sublimates and is a violent poison); Mercury fulminate, (a detonator widely used in explosives); Mercury(II) oxide, the main oxide of mercury; Mercury(II) sulfide (AKA cinnabar mercuric ore still used in oriental medicine, or vermilion which is a high-grade paint pigment); Mercury(II) selenide a semiconductor; Mercury(II) telluride a semiconductor; and Mercury cadmium telluride and mercury zinc telluride, infrared detector materials. Laboratory tests have found that an electrical discharge causes the noble gases to combine with mercury vapor. These compounds are held together with van der Waals forces and result in Hg·Ne, Hg·Ar, Hg·Kr, and Hg·Xe (see exciplex). Organic mercury compounds are also important. Methylmercury is a dangerous compound that is widely found as a pollutant in water bodies and streams. The discovery of Mercury(IV) fluoride (HgF4) was announced in September 2007. |
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