Of all the different precious metals we can think of, gold is certainly the one most greatly desired. Since the beginning of recorded history, gold has been in use in many different works of art, coinage, and, of course, jewelry. Occurring as grains in rocks and in alluvial deposits, gold is shiny, soft, and dense. It is known to be the most ductile and malleable pure metal.
What makes pure gold especially attractive is its bright yellow color and luster. These characteristics are maintained as gold is chemically unaffected by air or moisture. Here are some of the properties of gold:
General:
• Chemical Symbol: Au
• Atomic Number: 79
• Category (as an element): Transition Metal
• Group/ Period/ Block (in the Periodic Table): 11/ 6/ d
• Atomic Weight: 196.966569(4) g.mol-1
• Electron Configuration: [Xe] 4f14 5d10 6s1
Physical:
• Density (near room temperature): 19.30 g.cm-3
• Liquid Density (at melting point): 17.31 g.cm-3
• Melting Point: 1064.18°C, 1947.52°F, 1337.33°K
• Boiling Point: 2856°C, 5173°F, 3129°K
• Heat of Fusion: 12.55 kJ.mol-1
• Heat of Vaporization: 324 kJ.mol-1
Atomic:
• Oxidation States: -1, 1, 2, 3, 4, 5
• Electronegativity: 2.54 (Pauling scale)
• Atomic Radius: 144 picometre
• Covalent Radius: 136±6 picometre
• Van der Waals Radius: 166 picometre
• Ionization Energies: 890.1 kJ.mol-1 (first), 1980 kJ.mol-1 (second)
The term "gold" was derived from "geolu", an Old English Anglo-Saxon word which means "yellow". Its symbol "Au", on the other hand, originated from "aurum", the Latin word for "gold". The exact period when gold was first discovered could be a subject of dispute. While some accounts point to the year 1848 when gold was discovered in California, history tells us that this precious metal was already being used extensively by the ancient Egyptians, Romans, Greeks, Chinese, and South Americans.
Throughout history, gold has served as a measure of value and a symbol of wealth. It is one of the coinage metals (along with silver and copper). It is used, customarily and legally, as a means of payment or a medium of exchange. Gram and troy weight are the units of measurement used for gold. To indicate the amount of gold present in, say, a piece of jewelry, the term "carat" is used. A necklace, for instance, that is 24 carats means that it is made of pure gold.
While gold's price is determined through trading in the derivatives and gold markets, its daily benchmark price is provided in a procedure called the London Gold Fix. In this procedure, the price of the precious metal is determined each business day on the London market. The fixing is done twice - once in the morning and another in the afternoon. The latter actually was introduced about 49 years after the procedure itself was introduced, as a means of providing a price when US markets are open.
This gold-price fixing procedure is done by the five members of the London Gold Market Fixing Ltd., namely The Bank of Nova Scotia, Barclays Capital, Deutsche Bank AG London, HSBC, and Societe Generale Corporate & Investment Banking.
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The metallic chemical elements collectively known as precious metals are called as such because of their extreme rarity and high economic value. Precious metals occur naturally or are by-products of the processing of other less rare metals.
In order of increasing mass abundance (parts per billion), the precious metals are rhenium, rhodium, iridium, ruthenium, osmium, gold, platinum, palladium, and silver. These metals are not radioactive and are mostly used for industrial purposes and for jewelry.
Still, precious metals have some safety issues attached to them:
Rhenium:
Since rhenium is used in very small amounts, its toxicity is virtually unknown. The hazardous property of rhenium halide, for example, may be attributed either to rhenium itself or to the other elements that make up the compound. Another rhenium compound - potassium perrhenate - is known to have a median lethal dose much like that of sodium chloride (commonly known as table salt).
Rhodium:
Although rhodium is inert (being a noble metal, as almost all the other precious metals are), it can be reactive, especially if used as compounds. In its basic form, however, rhodium is not known to cause any harm.
Iridium:
Iridium, when finely divided, can pose some hazards - it can ignite in air. Apart from this, accidental exposure to a radioisotope of iridium may cause poisoning by radiation, burns, and even death.
Ruthenium:
Three conditions may be associated with exposure to ruthenium: it can stain the skin; it may accumulate in bones; and it may increase the risk of cancer. Ruthenium tetroxide, a yellow, diamagnetic tetrahedral ruthenium compound, is highly toxic and volatile; it may explode if it comes into contact with combustible materials.
Osmium:
Osmium, like iridium, can ignite spontaneously in air when in finely divided form. The compound osmium tetroxide, in particular, is highly volatile and is extremely toxic if accidentally inhaled, ingested, or comes into contact with the skin.
Gold:
Gold, in its elemental form, does not cause irritation and is not toxic even when ingested. In fact, it is used as a component in some alcoholic drinks and as a food additive. However, ionic chemical compounds of gold (example, gold chloride) can be extremely harmful to the kidneys and liver.
Platinum:
Findings by the U.S. federal agency CDC reveal that exposure to platinum salts, on the short term, may cause nose, throat, and eye irritation. Long-term exposure to these compounds, on the other hand, may cause skin and respiratory allergies.
Palladium:
Palladium in bulk metallic form is completely inert. The same can't be said though of the metal in finely divided form, which can readily ignite in air.
Silver:
Silver compounds (example, colloidal silver), when absorbed into the body, may cause argyria, a condition characterized by the bluish-gray pigmentation of the skin, mucous tissues, and the eyes. While the condition is not really harmful to one's health, it is often permanent. Otherwise, silver per se is not at all toxic.
It certainly is important to know that each of the precious metals has possible health hazards so that first-time handlers can take the necessary precautions.
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