Mercury (Hg)

Mercury is the only metallic element that exists in liquid form at room temperature and is located at the 80th position in the periodic table. This transition metal has attracted attention throughout history due to its shiny silvery appearance and fluidity. It has been known since ancient times. Its symbol Hg derives from the Latin word "hydrargyrum" meaning "liquid silver." Despite its use in various scientific and industrial applications due to properties such as high density uniform thermal expansion and electrical conductivity its use is now severely restricted because of its high toxicity.

Classification and Fundamental Properties

Mercury (Hg) is a transition metal located in the 6th period and 12th group of the periodic table. Its electron configuration is [Xe] 4f¹⁴5d¹⁰6s². These fully filled d and s orbitals result in relatively weak metallic bonding and cause the element to have unusually low melting and boiling points. As a result mercury is one of only two elements that are liquid under standard temperature and pressure conditions the other being bromine. Its density is approximately 13.53 g/cm³ making it a very heavy liquid. Although its thermal conductivity is low it is a good conductor of electricity.

Discovery

Mercury has been known since ancient times as it has been found in Egyptian tombs dating back to around 1500 BCE. Therefore it has no single discoverer. It was also known and used for various purposes by ancient Chinese Indian and Roman civilizations. Alchemists believed mercury to be the primordial substance from which all metals were formed and used it extensively in both philosophical and practical studies.

Origin of the Element's Name

The Turkish name "cıva" originates from Arabic and Persian. Its chemical symbol Hg derives from the Greek words "hydor" (water) and "argyros" (silver) combined into the Latin term "hydrargyrum" meaning "liquid silver." The English name "Mercury" comes from the Roman mythological god Mercury the swift and mobile messenger deity.

Natural Occurrence

Mercury is a relatively rare element in the Earth's crust. It occurs naturally only rarely in its free state as tiny droplets. The most common and commercially significant source of mercury is cinnabar (also known as vermilion or mercury(II) sulfide HgS) a bright red mineral. Mercury is obtained by heating cinnabar in air to approximately 600 °C (roasting). During this process sulfur is released as sulfur dioxide leaving behind mercury vapor which is then condensed to obtain liquid mercury. Major mercury deposits are found in Spain Italy Slovenia China Russia and the Americas. Mercury is also released into the environment through volcanic activity and the burning of fossil fuels.

Physical and Chemical Properties

Mercury has highly unique physical and chemical properties. It is a silvery white shiny liquid at room temperature. Its melting point is -38.829 °C and its boiling point is 356.619 °C. This wide liquid range is one of the main reasons for its use in thermometers. Its atomic radius is approximately 223 pm and its electronegativity value is 1.9. Mercury has very high surface tension which causes it to form spherical droplets rather than adhere to surfaces.

Chemically mercury is relatively unreactive. It does not dissolve in nonoxidizing acids but reacts with oxidizing acids such as nitric acid and hot concentrated sulfuric acid. It slowly oxidizes in air. In its compounds mercury typically exhibits two main oxidation states: +1 (mercurous as the [Hg₂]²⁺ ion) and +2 (mercuric as Hg²⁺). One of mercury's most notable chemical properties is its ability to dissolve many metals such as gold silver tin and zinc to form alloys known as amalgams.

Isotopes

Mercury has seven stable isotopes in nature: ¹⁹⁶Hg ¹⁹⁸Hg ¹⁹⁹Hg ²⁰⁰Hg ²⁰¹Hg ²⁰²Hg and ²⁰⁴Hg.

• ²⁰²Hg: This is the most abundant naturally occurring isotope of mercury (approximately 29.86%). It is also an important isotope in sources. In addition many radioactive isotopes have been artificially produced.

Applications

Although the use of mercury has been restricted or banned in many areas due to its high toxicity it still finds use in certain specialized applications:

• Chemical Industry: A small amount of mercury cells are still used in the production of chlorine and sodium hydroxide (chlor-alkali industry) but this technology is being phased out gradually.
• Measuring Instruments: Due to its low melting point and uniform thermal expansion mercury was widely used in thermometers manometers and barometers. However these uses are being discontinued following calls from the World Health Organization.
• Illumination: Fluorescent lamps compact fluorescent lamps (CFLs) and mercury vapor lamps contain small amounts of mercury vapor that emit ultraviolet light when an electric current passes through. This UV light strikes a phosphor coating on the inner surface of the lamp producing visible light.
• Electrical Devices: Mercury is used in some electrical switches and relays (mercury switches).
• Batteries: Mercury was previously used in the construction of certain batteries such as zinc-carbon alkaline and mercury oxide batteries but this use has largely ceased due to environmental concerns.
• Amalgams: An amalgam formed with silver tin copper and zinc was used for many years as a dental filling material ("silver filling"). This use is declining due to toxicity concerns and is being replaced by alternatives such as composite resins.
• Other Applications: Mercury has been used in the extraction of gold and silver from ores the production of certain explosives (mercury fulminate) and some laboratory applications.

Biological Importance Effects and Precautions

Mercury has no known biological role and is extremely toxic. Both elemental mercury and its inorganic and organic compounds especially methylmercury are hazardous to humans and other organisms. Mercury poisoning can occur through inhalation of mercury vapor ingestion of mercury compounds or absorption through the skin. Humans primarily acquire mercury by consuming fish and shellfish that have accumulated methylmercury formed in aquatic environments by bacteria. Mercury is a potent neurotoxin that particularly damages the central nervous system kidneys and liver. Mercury poisoning can lead to serious health problems such as tremors memory loss cognitive disorders muscle weakness and birth defects. Due to these dangers working with mercury and its compounds requires strict safety measures including good ventilation full protective clothing gloves and respiratory protection. Mercury spills must be cleaned up using specialized procedures.