Mercury
Hg
Atomic No. - 80
Mercury is also called 'quicksilver.'
The History Says
Mercury was known to the ancient Chinese and Hindus and was found in
Egyptian tombs that date from 1500 BC. The ancient Greeks used mercury
in ointments and the Romans used it in cosmetics. By 500 BC mercury
was used to make amalgams with other metals.
The Present Scenario
Today, mercuric medicines and devices are generally considered
hazardous. Neither are used to the extent they were in the past.
Mercury
is one of the five elements (caesium, francium, gallium and bromine)
which are liquid at room temperature. It is officially classes as a
mineral for historical reasons. It crystallizes at -40 degrees celsius
forming hexagonal crystals.
Mercury is a rare element in the earth's crust. In nature it is
usually found as small isolated drops which is associated with
cinnabar, corderoite, livingstonite, and other minerals with cinnabar
(HgS). Sometimes it is also found as large masses of fluid in rock
cavities, mainly in active volcanic regions.
It is extracted by heating cinnabar in a current of air and
condensing the vapor. Here follows the equation for the extraction:
HgS
+ O2 = Hg + SO2
Physical Properties of Mercury
| Phase |
Liquid |
| Density (near room temperature) |
(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 of capacity |
(25°C) 27.983 J/(mol-K) |
Atomic Properties of Mercury
| 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 |
Uses of Mercury
- For
the manufacturing of industrial chemicals or for electrical and
electronic applications.
- In
thermometers.
- As
mercury sphygmomanometers, a blood pressure meter.
- Thimerosal,
an organic compound is used as preservative in vaccines and tattoo
inks.
- As
mercury barometers, diffusion pumps, coulometers, and many more
laboratory instruments.
- In
mercury arc rectifier, a type of electrical rectifier that converts
alternate current into direct current.
- In
mercury-vapor lamps and some neon advertising signs and fluorescent
lamps.
- Once
used as coolant for nuclear reactors, which has been replaced by
sodium and also in the amalgamation process of refining gold and
silver ores.
- As
folk medicine and ceremonial purposes that involves ingestion,
injection, or the sprinkling of elemental mercury around the home.
- In
mercury switches, mercury cells and chlorine production, electrodes,
batteries, and catalysts.
- As
herbicides, insecticides, dental amalgams and liquid mirror
telescopes.
Health
and Mercury
Mercury poisoning is known as mercuralism. It is easily absorbed
through the skin, respiratory and gastrointestinal tissues in humans.
It attacks the central nervous system and endocrine system, adversely
affecting the mouth, gums, and teeth. Highe exposure of mercury and
over a longer period of time, it results in brain damage which can
even lead to death.
Mercury also poses major health risk to the unborn fetus. Poisoned
humans or animals often manifest excessive salivation. It is a
condition known as mercurial ptyalism. The disease Minamata is also a
form of mercury poisoning.
Precautions with Mercury
- The
containers of mercury should be covered to avoid spillage and
evaporation.
- Heating
either mercury or its compounds should be done under a
well-ventilated and filtered hood.
- Always
wash hand after handling mercury.
- Never
lick or ingest.
- Do
not inhale vapors.
Occurrences of Mercury
- Almaden,
Spain
- Idria,
Slovenia
- Russia
- North
America
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