Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80, commonly called quicksilver. It is a heavy, silvery d-block metal and holds the distinction of being the only metallic element that remains liquid under standard temperature and pressure. Mercury has the lowest freezing point and boiling point of any metal, giving it the narrowest liquid-state range of any metal under standard conditions. This unusual behavior arises from lanthanide contraction and relativistic contraction, which weaken the metallic bonding. When liquid mercury freezes, its volume shrinks by 3.59%, and its density increases from 13.69 g/cm³ to 14.184 g/cm³. Solid mercury is malleable and ductile, and can be cut with a knife. Mercury is a poor conductor of heat but a fair conductor of electricity. Near its critical point, it undergoes a metal-nonmetal transition with sharp changes in conductivity and optical properties. It was the first known superconductor, discovered in 1911 when cooling mercury below a certain temperature, though its superconductive properties later proved unusual compared to other superconductors. At room temperature, applying pressure solidifies mercury into a simple rhombohedral structure, and further compression yields at least four distinct solid allotropes, including a hexagonal-close-packed phase. Liquid mercury at high pressure shows an anomalously low coordination number, with each atom having around 6 to 10 nearest neighbors, unlike typical dense metallic liquids. Mercury occurs worldwide, primarily as cinnabar (mercuric sulfide), and the red pigment vermilion is made by grinding natural or synthetic cinnabar. It is somewhat more reactive than gold or platinum but more stable than zinc or cadmium. It reacts with oxidizing acids to form mercury(II) salts, and with hydrogen sulfide like silver does. Mercury dissolves many metals, including gold and silver, to form amalgams, though iron and several first-row transition metals resist amalgamation. Sodium amalgam is used as a reducing agent in organic synthesis and in high-pressure sodium lamps. Mercury readily amalgamates with aluminum, destroying its protective oxide layer and causing serious corrosion. Exposure to mercury and its organic compounds is toxic to the nervous system, immune system, and kidneys, and poisoning can occur through water-soluble forms like mercuric chloride or methylmercur