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Ag

Cd

In

Au

Hg

Tl

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Element Fact
Rhenium was the last naturally occurring element to be identified, in 1925. It was so rare that only 1 g of the metal was extracted out of 660 kg of molybdenite ore.

Mercury, Hg

mercury sample

Atomic number: 80
Atomic mass: 200.59(2)
Natural abundance: 0.08 ppm
Isotopes:
196Hg (195.965815) - 0.15%
198Hg (197.966752) - 9.97%
199Hg (198.968262) - 16.87%
200Hg (199.968309) - 23.10%
201Hg (200.970285) - 13.18%
202Hg (201.970626) - 29.86%
204Hg (203.973476) - 6.87%

History and Production

Derived from the planet Mercury. The symbol Hg is derived from the word hydrargyrum, meaning liquid silver. The element is known to ancient. It was found in Egyptian's tombs since 1500 BC. The mercury mineral cinnabar (HgS) was used as a pigment in the ancient world while extraction of the element from cinnabar and mercury amalgamation have been known since 500 BC. Up to 1500 AD, alchemists regarded the metal as a key to the transmutation of base metals to gold (which is obviously not true!). Nowadays, mercury is still obtained from cinnabar. The ore is simply roasted and the mercury vapor is condensed. Especially rich ores are usually roasted with scrap iron or quicklime (CaO). Further purification can be achieved by distillation under pressure. It has its important use in the Castner-Kellner process for manufacturing of chlorine and sodium hydroxide. Mercury is also used in the laboratory work for making thermometers and barometers. In electrical industry, as mercury-vapor lamps, electrical swithces and AC rectifiers. Certain mercury compounds have found their uses as germicides and fungicides.

Physical Data

It is one of the few metals that exists as liquid in room temperatures. It is heavy, and has a silvery-white in appearance. It easily forms amalgams with other metals such as gold, silver, tin and most other metals. The notable exceptions are iron, cobalt and nickel. Mercury is as abundant as silver, about 0.08 ppm, which exists mostly as cinnabar. The triple point of mercury, 38.8344C, is a fixed point on the International Temperature Scale (ITS-90).

Interatomic distance: 300.6 pm
Melting point: -38.83C
Boiling point: 356.73C
Thermal conductivity/Wm-1K-1: 8.34 (27C)
Density/kgm-3: 13546 (27C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 61.4 kJ/mol
Gibbs free energy of formation: 31.8 kJ/mol
Entropy: 175.0 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Xe] 4f14 5d10 6s2
Term symbol: 1S0
Electron affinity: (not stable)   Electronegativity (Pauline): 1.90
Ionization energy (first, second, third): 1007.07, 1809.68, 3299.80 kJ/mol

Chemical properties

Mercury is not reactive at room temperature. But at boiling point, it combines with oxygen to give the red mercury(II) oxide. However, at even higher temperature, the oxide decomposes to the metal. Mercury is readily react with ozone and halogens. It does not react with water or steam and dilute hydrochloric and sulfuric acids. However, mercury reacts with dilute nitric acid, giving mercury(I) nitrate. In excess concentrated nitric acid it gives mercury(II) nitrate.

Test for mercury:
On heating a mixture of a mercury compound and sodium carbonate in an ignition tube, a grey deposit of mercury is formed in the walls of the tube.

Test for mercury(I) ions:
(1) Addition of a chloride solution of hydrochloric acid gives a white precipitate, which blackened by ammonia.
(2)Sodium hydroxide gives a black precipitate.
(3) Tin(II) chloride causes reduction to a grey-black precipitate of mercury.

Test for mercury(II) ions:
(1) Hydrogen sulfide gives a balck precipitate, insoluble in ammonium sulfide but slightly soluble in dilute nitric acid.
(2) Sodium hydroxide gives a yellow precipitate of mercury(II) hydroxide.
(3) Tin(II) chloride reduces to a white precipitate of mercury(I) chloride and then to grey-black precipitate of mercury.


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