168 | The History and Use of Our Earth’s Chemical Elements Hazards
168 | The History and Use of Our Earth’s Chemical Elements Hazards
Pure gold, if ingested, can cause skin rash or even a sloughing off of skin. It can also cause kidney damage and problems with the formation of white blood cells.
MERCURY SYMBOL:Hg PERIOD:6 GROUP:12(IIB) ATOMICNO:80
ATOMICMASS:200.59amu VALENCE:1and2 OXIDATIONSTATE:+1and+2 NATURALSTATE:Liquid ORIGINOFNAME:NamedforthemythologicalRomangodoftravel,Mercurius,themessen- gertoothergods.ItssymbolHgisfromtheLatinword hydrargyrus,meaning“liquidsilver.” ISOTOPES:Thereareatotalof45isotopesoftheelementmercury.Sevenoftheseare stableandcontributetothetotalelement’snaturalexistenceonEarthasfollows.Hg-196 =0.15%,Hg-198=9.97%,Hg-199=16.87%,Hg-200=23.10%,Hg-201=13.18%, Hg-202=29.86%,andHg-204=6.87%.Alltheotherisotopesofmercuryareradioac- tivewithhalf-livesofafewmilliseconds,toafewseconds,toafewhours,andupto about500years.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=32
s2,p6,d10,f14
5-O=18
s2,p6,d10
6-P=2
s2
Properties Mercury is the only metal that is in a liquid state at room temperatures and remains liquid
at temperatures well below the freezing temperature of water. Mercury is a noncombustible, heavy, silvery-colored metal that evenly expands and contracts with temperature and does not “wet” or stick to glass, which makes it ideal as a liquid for thermometers. Mercury is slightly volatile and will give off toxic fumes, especially if heated. Its has a unique melting point of
–38.83°C, a boiling point of 3,56.73°C, and a density of 13.5336 g/cm 3 . Characteristics Mercury is located in group 12 (IIB) below Zn and Cd. Even though mercury is at the
end of the third series of transition elements, it is not always considered one of the transition elements.
169 Mercury forms alloys, called amalgams, with other metals such as gold, silver, zinc, and
Guide to the Elements |
cadmium. It is not soluble in water, but will dissolve in nitric acid. It has a high electric con- ductivity, making it useful in the electronics industry. However, unlike most other metals, it is a poor conductor of heat. Because of its high surface tension, it does not “wet” the surfaces that it touches. This characteristic also accounts for its breakup into tiny droplets when poured over a surface. If spilled, it should not be collected with bare hands, but with a thin piece of cardboard to scoop it up.
AbundanceandSource Mercury is the 68th most abundant element. Although it can occur in its natural state,
it is more commonly found as a sulfide of mercury. Its chief ore is cinnabar (HgS), which sometimes is called “vermilion” due to its red color. Historically, cinnabar was used as a red pigment. Today it is mined in Italy, Spain, and California. The best-known mercury mine is located at Almaden, Spain. It has been in continuous operation since 400 BCE.
Mercury is also found in black metacinnabar and mercury chloride. Small liquid droplets of mercury may be visible in high-grade deposits. Mercury ores are also found in Algeria, Mexico, Bosnia, and Canada as well as in Spain and California.
History The history of mercury extends over the past four thousand years; therefore, it is impos-
sible to attribute its discovery to any one individual. The Chinese used mercury before 2000 BCE, and vials of mercury have been found in ancient Egyptian tombs. Mercury and its ore cinnabar were well known to alchemists of the Dark and Middle Ages and were ingredients for preparing the “philosophers’ stone.” Alchemist-physicians used mercury to make “elixirs” to try to cure all illnesses, but this often killed the patients because mercury is a poison. It was also used in their “experiments” to convert base metals into gold. Metallic gold has an affinity for mercury, and it seems that mercury simply dissolves into the gold, turning it into a slivery color, leading the alchemists to incorrectly believe that mercury could in some way convert other metals into gold.
Joseph Priestley (1733–1804) heated mercury with air and formed a red powder (mercuric oxide) that, when heated in a test tube, produced small globs of mercury metal on the inside of the glass tube, as well as a gas that caused other substances to burn more rapidly than they did in air. Priestley did not know it at the time, but he had separated oxygen from the com- pound HgO.
Today, just about all mercury is produced via the reduction of cinnabar (HgS) by using a reducing agent, such as oxygen, iron, or calcium oxide (CaO). The resulting mercury vapor is passed through water where it liquefies (changes into its normal metallic state and sinks to the bottom of the water bath) while all the impurities float to the surface.
CommonUses One of the most common uses of mercury is to make amalgams, which are solid “solu-
tions” of various metals that can be combined without melting them together. Metals such as gold, silver, platinum, uranium, copper, lead, potassium, and sodium will form amalgams with mercury. The most common is silver-mercury amalgam, used as fillings for tooth cavities. Other types of fillings are now used since it has been proven that mercury, on contact with
170 | The History and Use of Our Earth’s Chemical Elements the skin of the mouth, can over time leach and act as a mild poison. Amalgams are also used
to extract mercury from its ores. Another common use is as a liquid contact in electrical “silent switches.” Also, mercury- vapor produces the bluish-white light of streetlights. However, mercury-vapor lights now are being replaced by sodium-vapor lights that produce a yellowish-white light. Mercury is used in thermometers and barometers, to coat mirrors, and in the electronics industry and several other industries.
Mercury batteries (cells) consist of a zinc anode and a mercuric oxide cathode. These cells produce a steady 1.3 volts throughout the cell’s lifetime.
The industrial uses of mercury are becoming more restrictive because of the element’s toxicity.
ExamplesofCompounds Almost all the stable mercury compounds are formed from the +1 and +2 oxidation states
of the element as follows:
Mercury (I) fluoride: 2Hg 1+ + 2F 1- → Hg 2 F 2 .
Mercury (II) chloride: Hg 2+ + 2Cl 1- → HgCl 2. This compound is used by the pharmaceutical industry and is used also as a fungicide, as a poison, in fireworks, and to control maggots. There are many other examples of mercury compounds used in industry. Mercury oxide (HgO) exists in two forms, red and yellow mercuric oxides, and is related
to mercurous oxide (Hg 2 O), which is black. All have industrial uses, ranging from antiseptics to pigments.
Mercuric sulfide (HgS) is a fine, very brilliant scarlet powder that is deadly if ingested. Also known as the mercury ore cinnabar and metacinnabar, it is used as a pigment in the manu- facture of paints.
Mercury fulminate [Hg(CNO) 2 ] is very explosive and is used to manufacture blasting caps and detonators.
Hazards Mercury metal is a very toxic and accumulative poison (it is not easily eliminated by the
body). When inhaled as vapors, ingested as the metal or as part of a compound, or even absorbed when in contact with the skin, it can build up to deadly amounts. The fumes of most compounds are poisonous and must be avoided. Anyone who ingests mercury should contact
a poison center immediately. If mercury metal is spilled, it needs to be carefully gathered so as not to spread the little globs, but rather combine them for easy collection.
Many patients are having the mercury amalgams that were used as dental fillings replaced because of their potential toxicity. There are conflicting data concerning the extent of risk resulting from the dental use of mercury amalgams, but there is some evidence that bacteria in saliva of the mouth may leach out traces of mercury from the amalgam. Regardless, different metals and plastics are preferred for use today to fill dental cavities.
Another danger is the waste mercury that has been deposited by industries and agricultural chemicals in the lakes and oceans of the world. Several decades ago most of the nations of the world approved an international ban on dumping mercury into our waterways and oceans. The problem is that smaller ocean plants and animals consume mercury. Larger fish consume
171 the mercury, and then we consume the larger animals. In turn, we receive an abundance of
Guide to the Elements |
accumulated mercury that has built up in our seafood chain. Most nations, including the United States, have banned the use of mercury in agricultural chemicals, including most pesti- cides and insecticides. In addition to being poisonous, some compounds of mercury (mercury fulminate) are extremely explosive.
Mercury can be a cumulative poison, which means that minor amounts absorbed over long periods of time build up until damage to internal organs occurs. Years ago, a mercury compound was used in the manufacturing process of felt hats. Workers who came in contact with the mercury developed a variety of medical problems, including the loss of hair and teeth and loss of memory along with general deterioration of the nervous and other systems. This became known as the “mad as a hatter” syndrome because of the afflicted individuals’ odd behavior.
Metallics—Metalloids—Semiconductors—Nonmetals