Mercury is a chemical element; it has symbol Hg (from Latin hydrargyrum) and atomic number 80. It is commonly known as quicksilver. A heavy, silvery d-block element, mercury is the only metallic element that is known to be liquid at standard temperature and pressure. As well as having the lowest freezing point, mercury has the lowest boiling point and subsequently the narrowest liquid state range of any metal at standard conditions.
Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). The red pigment vermilion is obtained by grinding natural cinnabar or synthetic mercuric sulfide. Exposure to mercury and mercury-containing organic compounds is toxic to the nervous system, immune system and kidneys of humans and other animals; mercury poisoning can result from exposure to water-soluble forms of mercury (such as mercuric chloride or methylmercury) either directly or through mechanisms of biomagnification.
Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, fluorescent lamps and other devices, but concerns about the element's toxicity have led to a reduction in the amount of mercury used in these instruments, or manufacturers not using it altogether. It remains in use in scientific research applications and in amalgam for dental restoration in some locales. It is also still used in fluorescent lighting, although the quantity of mercury used is now smaller. Electricity passed through mercury vapor in a fluorescent lamp produces short-wave ultraviolet light, which then causes the phosphor in the tube to fluoresce, making visible light.
Properties Physical properties
Mercury is a heavy, silvery-white metal. It is the only metallic element that is known to be liquid at standard temperature and pressure; the only other element that is liquid under these conditions is bromine, one of the halogens, though metals such as caesium, gallium, and rubidium melt just above room temperature. Compared to other metals, mercury is a poor conductor of heat, but a fair conductor of electricity. in
Mercury has a melting point of and a boiling point of both the lowest of any stable metal, resulting in the lowest stable liquid-state range of any metal under standard conditions. This effect is due to lanthanide contraction and relativistic contraction reducing the orbit radius of the outermost electrons, and thus weakening the metallic bonding in mercury. Upon freezing, the volume of mercury decreases by 3.59% and its density changes from 13.69 g/cm3 when liquid to 14.184 g/cm3 when solid. The coefficient of volume expansion is 181.59 × 10−6 at 0 °C, 181.71 × 10−6 at 20 °C and 182.50 × 10−6 at 100 °C (per °C). Solid mercury is malleable and ductile, and can be cut with a knife.
When expanded by heating near its critical point (around and ), mercury exhibits a metal-nonmetal transition associated with sharp changes in its electronic conductivity and optical properties.
Mercury was the first known superconductor, discovered in 1911 by Heike Kamerlingh Onnes by cooling of mercury below shortly after the discovery and production of liquid helium. Its superconductive properties were later determined to be unusual compared to other later-discovered superconductors, such as the more popular niobium alloys.
At room temperature (), liquid mercury solidifies into a simple rhombohedral structure at approximately of pressure. On further compression, mercury undergoes several structural phase transitions into at least four distinct solid allotropes as compression increases, where the δ-phase with an hexagonal-close-packed (hcp) structure is stable above until at least . The melting curve at high-pressure increases steeply on initial compression, but exhibits a pronounced flattening and a potential local maximum at around . At ), liquid mercury exhibits an anomalously low first-shell coordination number, with each Hg atom having around 6 to 10 nearest neighbours, in contrast to simple metallic liquids in which atoms are densely-packed with 12 nearest neighbours. At simultaneous high-pressure and temperature conditions, the atomic arrangement in liquid mercury progresses towards a simple densely packed liquid structure. However, even at very high pressures (up to around ), liquid mercury retains more many-body clusters than expected for a simple hard-sphere liquid.
Chemical properties Mercury is somewhat more reactive than the noble metals gold and platinum that are close to it in the periodic table, but it is more stable than other the group 12 metals, zinc and cadmium. It reacts with oxidizing acids such as concentrated sulfuric acid and nitric acid or aqua regia to give mercury(II) sulfate, mercury(II) nitrate, and mercury(II) chloride, respectively. Like silver, mercury reacts with atmospheric hydrogen sulfide. Mercury reacts with solid sulfur flakes, which are used in mercury spill kits to absorb mercury (spill kits also use activated carbon and powdered zinc).
Amalgams Mercury dissolves many metals such as gold and silver to form amalgams. Iron is an exception, and iron flasks have traditionally been used to transport the material. Several other first row transition metals (with the exception of manganese, copper and zinc) are also resistant in forming amalgams. Other elements that do not readily form amalgams with mercury include platinum. Sodium amalgam is a common reducing agent in organic synthesis, and is also used in high-pressure sodium lamps.
Mercury readily combines with aluminium to form a mercury-aluminium amalgam when the two pure metals come into contact. Since the amalgam destroys the aluminium oxide layer which protects metallic aluminium from oxidizing in-depth (as in iron rusting), even small amounts of mercury can seriously corrode aluminium. For this reason, mercury is not allowed aboard an aircraft under most circumstances because of the risk of it forming an amalgam with exposed aluminium parts in the aircraft.
Mercury embrittlement is the most common type of liquid metal embrittlement, as mercury is a natural component of some hydrocarbon reservoirs and will come into contact with petroleum processing equipment under normal conditions.
Isotopes
There are seven stable isotopes of mercury, with Hg being the most abundant (29.86%). The longest-lived radioisotopes are Hg with a half-life of 444 years, and Hg with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day. Hg occurs naturally in tiny traces as an intermediate decay product of U. Hg and Hg are the most often studied NMR-active nuclei, having spins of and respectively.
Etymology
Hg is the modern chemical symbol for mercury. It is an abbreviation of , a romanized form of the ancient Greek name for mercury, (). Hydrargyrum ( ) Random House Webster's Unabridged Dictionary. has also been used in English, though the term is now dated. is a Greek compound word meaning , from - (-), the root of () , and () . Like the English name quicksilver (), this name was due to mercury's liquid and shiny properties.
The modern English name mercury comes from the planet Mercury. In medieval alchemy, the seven known metals—quicksilver, gold, silver, copper, iron, tin, and lead—were associated with the seven classical planets (Mercury, the sun, moon, Venus, Mars, Jupiter, and Saturn respectively). Quicksilver was associated with the fastest planet, which had been named after the Roman god Mercury, who was associated with speed and mobility. The astrological symbol for the planet became one of the alchemical symbols for the metal, and Mercury became an alternative name for the metal. Mercury is the only metal for which the alchemical planetary name survives, as it was decided it was preferable to quicksilver as a chemical name.Maurice Crosland (2004) Historical Studies in the Language of Chemistry
History Mercury was found in Egyptian tombs that date from 1500 BC; cinnabar, the most common natural source of mercury, has been in use since the Neolithic Age.
In China and Tibet, mercury use was thought to prolong life, heal fractures, and maintain generally good health, although it is now known that exposure to mercury vapor leads to serious adverse health effects. The first emperor of a unified China, Qín Shǐ Huáng Dì—allegedly buried in a tomb that contained rivers of flowing mercury on a model of the land he ruled, representative of the rivers of China—was reportedly killed by drinking a mercury and powdered jade mixture formulated by Qin alchemists intended as an elixir of immortality. Khumarawayh ibn Ahmad ibn Tulun, the second Tulunid ruler of Egypt (r. 884–896), known for his extravagance and profligacy, reportedly built a basin filled with mercury, on which he would lie on top of air-filled cushions and be rocked to sleep.
Quantities of liquid mercury, ranging from have been recovered from a chamber below the 1800-year-old pyramid known as the Temple of the Feathered Serpent, the third-largest pyramid of Teotihuacan, Mexico, along with "jade statues, jaguar remains, a box filled with carved shells and rubber balls". In Lamanai, once a major city of the Maya civilization, a pool of mercury was found under a marker in a Mesoamerican ballcourt. This mercury may have been used in bowls as mirrors for divinatory purposes. Five of these date to the Classic Period of Maya civilization (c. 250–900) but one example predated this.
Aristotle recounts that Daedalus made a wooden statue of Aphrodite move by pouring quicksilver in its interior. Text In Greek mythology Daedalus gave the appearance of voice in his statues using quicksilver. The ancient Greeks used cinnabar (mercury sulfide) in ointments; the ancient Egyptians and the Romans used it in cosmetics. By 500 BC mercury was used to make amalgams (Medieval Latin amalgama, "alloy of mercury") with other metals.
Alchemists 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 called for in attempts at the transmutation of base (or impure) metals into gold, which was the goal of many alchemists.
The mines in Almadén (Spain), Monte Amiata (Italy), and Idrija (now Slovenia) dominated mercury production from the opening of the mine in Almadén 2500 years ago, until new deposits were found at the end of the 19th century.
Beginning in 1558, with the invention of the patio process to extract silver from ore using mercury, mercury became an essential resource in the economy of Spain and its American colonies. Mercury was used to extract silver from the lucrative mines in New Spain and Peru. Initially, the Spanish Crown's mines in Almadén in Southern Spain supplied all the mercury for the colonies. Mercury deposits were discovered in the New World, and more than 100,000 tons of mercury were mined from the region of Huancavelica, Peru, over the course of three centuries following the discovery of deposits there in 1563. In 1786 the main mine at Huancavelica suffered a sudden collapse that killed over 100 persons and greatly reduced the mine's output. Through the legalization of scavenging known as pallaqueo mercury production rose again peaking in 1794–1796. The French Revolutionary Wars disrupted European mercury supply to Spanish America leading to an increasing reliance for the mines in present-day Peru and Bolivia on mercury from Huancavelica but this mines production was clearly by 1799 not enough to supply the demand in the Andean mines. Spain abolished the royal mercury monopoly in 1813.
Mercury poisoning in the mines left many people disabled through the early modern period but mercury itself was not the chief cause of deaths in the mines.