Mercury (element)

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80 gold ← mercury → thallium
Cd
↑
Hg
↓
Uub
Image:Hg-TableImage.png
General
Name, Symbol, Number mercury, Hg, 80
Chemical series transition metals
Group, Period, Block 12, 6, d
Appearance silvery white
Image:Hg,80b.jpg
Atomic mass 200.59(2) g/mol
Electron configuration [Xe] 4f14 5d10 6s2
Electrons per shell 2, 8, 18, 32, 18, 2
Physical properties
Phase liquid
Density (near r.t.) (liquid) 13.534 g/cm³
Melting point 234.32 K
(-38.83 °C, -37.89 °F)
Boiling point 629.88 K
(356.73 °C, 674.11 °F)
Heat of fusion 2.29 kJ/mol
Heat of vaporization 59.11 kJ/mol
Heat capacity (25 °C) 27.983 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 315 350 393 449 523 629
Atomic properties
Crystal structure rhombohedral
Oxidation states 2, 1
(mildly basic oxide)
Electronegativity 2.00 (Pauling scale)
Ionization energies 1st: 1007.1 kJ/mol
2nd: 1810 kJ/mol
3rd: 3300 kJ/mol
Atomic radius 150 pm
Atomic radius (calc.) 171 pm
Covalent radius 149 pm
Van der Waals radius 155 pm
Miscellaneous
Magnetic ordering diamagnetic
Electrical resistivity (25 °C) 961 nΩ·m
Thermal conductivity (300 K) 8.30 W/(m·K)
Thermal expansion (25 °C) 60.4 µm/(m·K)
Speed of sound (liquid, 20 °C) 1451.4 m/s
CAS registry number 7439-97-6
Notable isotopes
Main article: Isotopes of mercury
iso NA half-life DM DE (MeV) DP
194Hg syn 444 y ε 0.040 194Au
195Hg syn 9.9 h ε 1.510 195Au
196Hg 0.15% Hg is stable with 116 neutrons
197Hg syn 64.14 h ε 0.600 197Au
198Hg 9.97% Hg is stable with 118 neutrons
199Hg 16.87% Hg is stable with 119 neutrons
200Hg 23.1% Hg is stable with 120 neutrons
201Hg 13.18% Hg is stable with 121 neutrons
202Hg 29.86% Hg is stable with 122 neutrons
203Hg syn 46.612 d β- 0.492 203Tl
204Hg 6.87% Hg is stable with 124 neutrons
References

Mercury, also called quicksilver, is a chemical element in the periodic table that has the symbol Hg (from the Greek hydrargyrum, for 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 (the others are the metals caesium, francium, and gallium, and the nonmetal bromine). Mercury is used in thermometers, barometers and other scientific apparatuses, although the use of mercury in thermometers has been largely phased out in clinical and scientific environments (in favor of alcohol-filled, digital or thermistor-based replacements) in the interests of health and safety due to the toxicity of the element. Mercury is mostly obtained by reduction from the mineral cinnabar.

Contents

Notable characteristics

Mercury is a relatively poor conductor of heat but is a good conductor of electricity.

Mercury easily forms alloys with almost all common metals, including gold, aluminium, and silver, but not iron. Tellurium forms an alloy also, but it reacts slowly to form mercury telluride. Any of these alloys is called an amalgam.

This metal also has uniform volumetric thermal expansion, is less reactive than zinc and cadmium and does not displace hydrogen from acids. Common oxidation states of this element are +1 and +2. Rare instances of +3 mercury compounds exist.

The commercial unit for handling mercury is the "flask," which weighs 76 lb (34.5 kg).

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 (Non-prescription sale of mercury fever thermometers was banned by a number of different states and localities). Other uses:

Miscellaneous uses: mercury switches, mercury cells for sodium hydroxide and chlorine production, electrodes in some types of electrolysis, batteries (mercury cells), and catalysts, herbicides (discontinued in 1995), insecticides, dental amalgams/preparations and liquid mirror telescopes.

Historical uses: preserving wood, developing daguerreotypes, silvering mirrors, anti-fouling paints (discontinued in 1990), cleaning, and in road leveling devices in cars. Mercury compounds have been used in antiseptics, laxatives, antidepressants, and antisyphilitics. It was also allegedly used by allied spies to sabotage German planes. A mercury paste was applied on bare aluminum, causing the metal to rapidly corrode. This would cause the planes to mysteriously fall apart.

History

Image:HG-alchemical.PNG

Mercury was known to the ancient Chinese and Hindus and was found in Egyptian tombs that date from 1500 BCE. In China, India and Tibet, mercury use was thought to prolong life, heal fractures, and maintain generally good health. The ancient Greeks used mercury in ointments and the Romans used it in cosmetics. By 500 BCE mercury was used to make amalgams with other metals.

The Indian word for alchemy is Rassayana which means ‘the way of mercury.’ Alchemists often thought of mercury as the first matter from which all metals were formed. Different metals could be produced by varying the quality and quantity of sulfur contained within the mercury. An ability to transform mercury into any metal resulted from the essentially mercurial quality of all metals. The purest of these was gold, and mercury was required for the transmutation of base (or impure) metals into gold. This was a primary goal of alchemy, either for material or spiritual gain.

Hg is the modern chemical symbol for mercury. It comes from hydrargyrum, a Latinized form of the Greek word `Υδραργυρος (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 (above left). Mercury is the only metal for which the alchemical planetary name became the common name.

From the mid-18th to the mid-19th centuries, a process called "carroting" was used in the making of felt hats. Animal skins were rinsed in an orange solution of the mercury compound mercuric nitrate, Hg(NO3)2•2H2O. This process separated the fur from the pelt and matted it together. This solution and the vapors it produced were highly toxic. Its use resulted in widespread cases of mercury poisoning among hatters. Symptoms included tremors, emotional lability, insomnia, dementia and hallucinations. The United States Public Health Service banned the use of mercury in the felt industry in December 1941. The psychological symptoms associated with mercury poisoning may have inspired the simile "mad as a hatter", and thereby the Mad Hatter of Alice in Wonderland fame.

Dentistry

Elemental mercury is the main ingredient in dental amalgams. Controversy over the health effects from the use of mercury amalgams began shortly after its introduction into the western world, nearly 200 years ago. In 1843, The American Society of Dental Surgeons, concerned about mercurial poisoning, required its members to sign a pledge that they would not use amalgam. In 1859, The American Dental Association was formed by dentists who believed amalgam was, "safe and effective." The ADA, "continues to believe that amalgam is a valuable, viable and safe choice for dental patients," as written in their statement on dental amalgam . In 1993, the United States Public Health Service reported that, "amalgam fillings release small amounts of mercury vapor," but in such a small amount that it, "has not been shown to cause any … adverse health effects." In 2002, California became the first state to ban the future use of mercury fillings (effective 2006). As of 2005, the controversy continues.

Medicine

Mercury has been used in the treatment of illnesses for centuries. Mercury(I) chloride and mercury(II) chloride were popular compounds. Mercury was included in the treatment of syphilis as early as the 16th century, before the advent of antibiotics. "Blue mass," a small pill in which mercury is the main ingredient, was prescribed throughout the 1800s for numerous conditions including, constipation, depression, child-bearing and toothaches (National Geographic). In the early 20th century, mercury was administered to children yearly as a laxative and dewormer. It was a teething powder for infants and some vaccines have contained the preservative Thimerosal (partly ethyl mercury) since the 1930s (FDA report). Mercury(II) chloride was a disinfectant for doctors, patients and instruments.

Mercury in the form of cinnabar remains an important component of Chinese, Tibetan, and Ayurvedic medicine. As problems may arise when these medicines are exported to countries that prohibit the use of mercury in medicines, in recent times, less toxic substitutes have been devised.

Today, mercuric medicines and devices are generally considered hazardous. Neither are used to the extent they were in the past. Thermometers and sphygmomanometers containing mercury were invented in the early 18th and late 19th centuries, respectively. In the early 21st century, their use is declining and has been banned in some countries, states and medical institutions. In 2002, the U.S. Senate passed legislation to phase out the sale of non-prescription mercury thermometers. In 2003, Washington and Maine became the first states to ban mercury blood pressure devices (HCWH News release). In 2005, mercury compounds are found in some OTC medications, including, topical antiseptics, stimulant laxatives, diaper rash ointment, eye drops and nose sprays. The FDA has "inadequate data to establish general recognition of the safety and effectiveness," of the mercury ingredients in these products (Code of federal regulations).

Mineral occurrence

Image:MercuryOreUSGOV.jpg

A rare element in the earth's crust, mercury is found either as a native metal (rare) or in cinnabar, corderoite, livingstonite, and other minerals with cinnabar (HgS) being the most common ore. Approximately 50% of the global supply comes from Almaden (Spain) and Idria (Slovenia), with much of the rest coming from Russia, and North America. The metal is extracted by heating cinnabar in a current of air and condensing the vapor. The equation for this extraction is

HgS + O2 → Hg + SO2

Compounds

The most important salts are:

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 HgNe, HgAr, HgKr, and HgXe. Organic mercury compounds are also important. Methylmercury is a dangerous compound that is widely found as a pollutant in water bodies and streams.

Isotopes

There are seven stable isotopes of mercury with Hg-202 being the most abundant (29.86%). The longest-lived radioisotopes are Hg-194 with a half-life of 444 years, and Hg-203 with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lifes that are less than a day.

Occurrence in the environment

Image:Mercury fremont ice core.png

Preindustrial deposition rates of mercury from the atmosphere may be in the range of 4 ng/L in the western USA. Although that can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric source by 4–6 times. [1]

Mercury enters the environment as a pollutant from various industries:

  • coal-fired power plants are the largest source (40% of USA emissions in 1999, which have since declined by 85%). [2]
  • industrial processes
  • medical applications, including vaccinations
  • laboratory work involving mercury or sulfur compounds

Mercury also enters into the environment through the disposal (e.g., landfilling, incineration) of certain products. Products containing mercury include: auto parts, batteries, fluorescent bulbs, medical products, thermometers, and thermostats.[3] Due to health concerns (see below), toxics use reduction efforts are cutting back or eliminating mercury in such products. For example, most thermometers now use pigmented alcohol instead of mercury. Mercury thermometers are still occasionally used in the medical field because they are more accurate than alcohol thermometers, though both are being replaced by electronic thermometers. Mercury thermometers are still widely used for certain scientific applications because of their greater accuracy and working range.

One of the worst industrial disasters in history was caused by the dumping of mercury compounds into Minamata Bay, Japan. The Chisso Corporation, a fertilizer and later petrochemical company, was found responsible for polluting the bay from 1932–1968. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease.

Health and Environmental Effects

See mercury poisoning.

Precautions and Regulation

Mercury should be handled with great care. Containers of mercury need to be covered securely to avoid spillage and evaporation. Heating of mercury or mercury compounds should always be done under a well-ventilated, filtered hood. Additionally, some oxides can decompose into elemental mercury, which immediately evaporates and may not be apparent.

Due to the health effects of mercury exposure, industrial and commercial uses are broadly regulated in Western countries. The World Health Organization, OSHA, and NIOSH, all agree that mercury is an occupational hazard and have established specific occupational exposure limits. Environmental releases and disposal of mercury is regulated in the U.S. primarily by the EPA.

In recent years, governments have issued warnings that certain fish in excess quantities are unsafe due to methylmercury levels (death has been known to occur from mercury contaminated fish). Such warnings especially target pregnant women.

The Clean Air Act, passed in 1990, put mercury on a list of toxic pollutants which need to be controlled to the greatest possible extent. Thus, certain industries that emit mercury into the environment must install maximum achievable control technologies (MACT). However, a March 2005 EPA rule[4] took power plants off the list of sources which must reduce mercury to the maximum extent. Instead, a cap and trade rule was issued, with most of the reductions in mercury pollution from power plants beginning in the year 2018. That rule is thought to be illegal and is being challenged by at least 13 states in court.

Mercury transport by aircraft is restricted, due to mercury's ability to rapidly "rust" aluminium, a primary structural component in most modern passenger aircraft.

References

History

  • American Dental Association. (2004, January 09). ADA statement on dental amalgam. Retrieved April 10, 2005.
  • Brown, R.H. (2003, December 19). Mercury’s fall from medicine to toxin. Georgia Public Policy Foundation. Retrieved April 03, 2005. "Permission to reprint in whole or in part is hereby granted, provided the author and his affiliations are cited."
  • Goldwater, L.J. (1955). Hat Industry. In: Mercury; a History of Quicksilver. York Press. Retrieved April 09, 2005.
  • Kelly, E. (1676). The stone of the philosophers. Transcribed by: L. Roberts. Retrieved April 03, 2005.
  • Mercury in Schools. (2004, August 20). Mercury through the Ages. Retrieved April 05, 2005.
  • U.S. Food and Drug Administration. (2004, April 1). Drugs for human use: New drugs. In: Food and drugs. Code of Federal Regulations. Retrieved April 03, 2005.

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