Mercury

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Mercury,  80Hg
Liquid Mercury by Bionerd from Wikipedia.jpg
Liquid mercury being poured in a glass, displaying high surface tension.
General properties
Name, symbol Mercury, Hg
Alternative names Hydrargyrum (Latin)
Quicksilver
Appearance Shiny silvery dense liquid
Mercury in the periodic table
Cd

Hg

Cp
GoldMercuryThallium
Atomic number 80
Standard atomic weight (Ar) 200.592(3)
Group, block , d-block
Period period 6
Electron configuration [Xe] 4f14 5d10 6s2
per shell
2, 8, 18, 32, 18, 2
Physical properties
Silvery
Phase Liquid
Melting point 234.321 K ​(−38.829 °C, ​−37.8922 °F)
Boiling point 629.88 K ​(356.73 °C, ​674.11 °F)
Density near r.t. 13.534 g/cm3
when liquid, at  10.66 g/cm3
Triple point 234.3156 K, ​1.65×10−7 kPa
Critical point 1750 K, 172 MPa
Heat of fusion 2.29 kJ/mol
Heat of 59.11 kJ/mol
Molar heat capacity 27.983 J/(mol·K)
 pressure
Atomic properties
Oxidation states +4, +2, +1, −2 ​(+1 and +2 are most common)
Electronegativity Pauling scale: 2.00
energies 1st: 1007.1 kJ/mol
2nd: 1810 kJ/mol
3rd: 3300 kJ/mol
Atomic radius empirical: 151 pm
Covalent radius 132±5 pm
Van der Waals radius 155 pm
Miscellanea
Crystal structure
Speed of sound 1451.4 m/s (liquid, at 20 °C)
Thermal expansion 60.4 µm/(m·K) (at 25 °C)
Thermal conductivity 8.30 W/(m·K)
Electrical resistivity 961 nΩ·m (at 25 °C)
Magnetic ordering diamagnetic
CAS Registry Number 7439-97-6
History
Discovery Ancient Chinese and Indians (before 2000 BCE)
· references

Mercury (also known as quicksilver) is a chemical element with the symbol Hg (from its latin name hydrargyrum, meaning silver water) and atomic number 80. It is the only liquid metal at room temperature.

Properties

Chemical

Mercury is resistant to most acids, although oxidizing acids, such as concentrated sulfuric acid, nitric acid or aqua regia dissolve it to give its respective sulfate, nitrate, and chloride salts. Mercury has two potential oxidation states (I) and (II). Mercury(I) nitrate, or mercurous nitrate, can be prepared by dissolving mercury in cold dilute nitric acid, while mercury(II) nitrate, mercuric nitrate, can be prepared by dissolving the metal in hot concentrated nitric acid. Like silver, mercury reacts with atmospheric hydrogen sulfide, but unlike silver will also react with solid sulfur, forming mercury sulfide (cinnabar). Elemental sulfur is used to absorb mercury spills and vapors. Mercury will also form amalgams with several metals such as gold, aluminium or alkali metals.

Physical

Mercury is a dense, silvery-white liquid metal. It is a poor conductor of heat, but a fair conductor of electricity. Mercury melts at −38.83 °C and boils at 356.73 °C. Unlike most metals that melt at low temperatures, liquid mercury does not wet glass. This property allows him to be easily cleaned from insoluble impurities and being easier to remove if it's spilled on a surface.

Availability

Mercury can be found in medical mercury thermometers. The packaging of these thermometers comes with a warning, that the product contains mercury and is dangerous for the environment. Old blood pressure meters also contain mercury. Other old devices that contain mercury are: old tilt switches, mercury electrodes, mercury manometers, mercury batteries, etc. Old amalgam fillings contain mercury. Some light sources, such as fluorescent lamps contain a minute amount of mercury, albeit too small to be of any importance.

In EU the sale of mercury is restricted.

Norway enacted a total ban on the use of mercury in the manufacturing and import/export of mercury products, in 2008.

Isolation

Mercury can be prepared by reducing its salt with a reducing metal, such aluminium, in an aqueous solution. The aqueous solution also has the advantage of destroying any Hg-Al amalgam. However, a better choice would be to use copper. If you use iron, you'll end up with "powdered" mercury, basically mercury mixed with iron impurities, and it's not very easy to purify it. While you can add a non-oxidizing acid or a base to remove the impurities and coalesce the mercury, a better method involves adding metallic copper, which will absorb the mercury droplets, which means that you're better off just using copper in the first place.

A more dangerous method involves roasting cinnabar in a current of air and condensing the resulting mercury vapor. This method is extremely dangerous, as it generate highly toxic mercury vapors.

"Dirty" mercury can be purified by squeezing it through a cloth or through a cotton in a syringe, and collecting the spills in a glass container. This works because mercury does not wet organic materials.

Projects

The use of mercury and mercury compounds in experiments carries a high risk of poisoning, mainly due to its vapors and the volatility of some of its compounds. The biggest risk however, is due to the low LD50 of most of its compounds, their ability to be absorbed through the skin and long delay between poisoning and first symptoms. Any experiments must be performed either outside, in a fume hood or, if possible in a glovebox.

Handling

Safety

Elemental mercury in its liquid form is not very reactive, but its vapors and compounds are extremely toxic. Mercury ions have a long half life in the body, and are potent cumulative toxins. If the metal is dropped onto a porous surface, such as wood, the metal can split into micron-sized beads which will evaporate and fill the room with extremely toxic mercury vapor. Many compounds can rapidly absorb through the skin and cause severe mercury poisoning. This leads to severe medical problems and can eventually lead to death, usually after a longer period of time.

Storage

Mercury should be stored in closed glass or thick plastic bottles, in a special hazardous substance cabinet, with a proper label. A bed of elemental sulfur can also be used, to absorb the leaking mercury vapors.

Mercury compounds should be stored in a similar way.

Disposal

Mercury spillings can be removed by adding a mixture of powdered elemental sulfur and zinc. The resulting solid must be taken to special disposal centers.

References

Relevant Sciencemadness threads