In the periodic table of the chemical elements, six metallic elements - all transition metals - are clustered together and lie in the d-block (the d-block in the periodic table refers to groups 8, 9, and 10, periods 5 and 6). These six elements are collectively referred to as the platinum group metals.

Of this group of metals, platinum is considered the most widely traded, as it is extensively used in the following: catalytic converters; dental alloys and other dentistry equipment; electrical conductors; resistive thermal devices, laboratory dishes and such other equipment capable of resisting chemical attack even in high temperature; and, of course, jewelry.

As a transition element, platinum is gray-white in appearance. Often because of this, it is mistaken for silver. Its other physical characteristics include its being malleable, ductile, and dense. But while platinum is generally resistant to corrosion, it is corroded by certain elements, such as cyanides (potassium cyanide or sodium cyanide), caustic alkalis, sulfur, and any of the five halogens (astatine, bromine, chlorine, fluorine, and iodine).

The following lists some of the properties of platinum:

General:

* Chemical Symbol: Pt

* Atomic Number: 78

* Category (as an element): Transition Metal

* Group/ Period/ Block (in the Periodic Table): 10/ 6/ d

* Atomic Weight: 195.084 g.mol-1

* Electron Configuration: [Xe] 4f14 5d9 6s1

Physical:

* Density (near room temperature): 21.45 g.cm-3

* Liquid Density (at melting point): 19.77 g.cm-3

* Melting Point: 1768.3°C, 3214.9°F, 2041.4°K

* Boiling Point: 3825°C, 6917°F, 4098°K

* Heat of Fusion: 22.17 kJ.mol-1

* Heat of Vaporization: 469 kJ.mol-1

Atomic:

* Oxidation States: 6, 5, 4, 3, 2, 1, -1, -2

* Electronegativity: 2.28 (Pauling scale)

* Atomic Radius: 139 picometre

* Covalent Radius: 136±5 picometre

* Van der Waals Radius: 175 picometre

* Ionization Energies: 870 kJ.mol-1 (first), 1791 kJ.mol-1 (second)

Platinum is known to occur as only three thousandth parts-per notation (0.003 ppm) in the Earth's crust. This makes it an extremely rare metal.

Compared to gold, platinum is more precious, although its price is considered more volatile. One of the reasons for this is that its demand is driven by industrial uses or applications. For example, its price tends to be double that of gold's when world economy is stable, but significantly goes down in times of economic uncertainty.

Because it's wear-resistant and does not tarnish, platinum is highly valued by jewelers, especially watchmakers. In 2008, its price went up to as high as 2,252 U.S. dollars per troy ounce.

Being rare and, therefore, very precious, platinum has been made synonymous to things that are considered "of the highest quality". We hear for instance of a platinum debit card holder enjoying a wide range of privileges; or of a platinum award being handed out to a music album that has sold over a million copies.

Platinum's rarity and preciousness has been so pronounced in fact as early as the Eighteenth century, that then French King Louis XV even made a declaration making platinum "the only metal fit for a king".

 

A metal is considered "precious" if it is rare and is of high economic value. Under these two factors, nine metallic chemical elements qualify as precious metals. These are, in no particular order, gold, palladium, silver, rhodium, iridium, ruthenium, platinum, osmium, and rhenium.

So that while the chemical element tellurium is considered one of the rarest element in the Earth's crust (its mass abundance being the same as that of rhodium, iridium, and ruthenium), its estimated price is only less than 5 U.S. dollars per troy ounce, and, therefore, cannot be considered a precious metal. The same can be said of bismuth, which has a mass abundance half less than that of palladium, but with a price of only a little more than a tenth of tellurium's price.

In terms of mass abundance, expressed in parts per billion (ppb), here's how the nine precious metals are ranked (rare to rarest): 9th: silver (75 ppb); 8th: palladium (15 ppb); 7th: gold (4 ppb); 6th: osmium (1.5 ppb); 5th to 3rd: iridium, rhodium, and ruthenium (1 ppb); 2nd: rhenium (0.7 ppb); and 1st: platinum (0.003 ppb).

The ranking appears different when the estimated world market prices, per troy ounce, of these nine precious metals are considered (estimates as of January 2010):

1st: Rhodium - USD2,750

2nd: Platinum - USD1,555

3rd: Gold - USD1,131

4th: Palladium - USD424

5th: Iridium - USD408

6th: Osmium - USD380

7th: Rhenium - USD194

8th: Ruthenium - USD173

9th: Silver - USD18

Of the nine precious metals, gold and silver are the best known. Apart from being traditional coinage metals (along with copper), both gold and silver are also well known for their uses in jewelry and art; they likewise have certain industrial uses.

A third important factor that will qualify an element as a precious metal, as may be noted from the uses of gold and silver above, is that it should not be radioactive. Thus, the chemical elements actinium, polonium, and radium are not considered precious metals because they are highly radioactive.

Compared to most other elements, precious metals are chemically less reactive, have higher melting points, and are more ductile - properties that make them ideal for many commercial and industrial applications.

In earlier times, precious metals were mainly used as currency. Today, however, they are highly regarded as investment and industrial commodities. Four of them, in fact - silver, gold, platinum, and palladium -, are minted into coins or cast into ingots and traded on commodity markets. All four are assigned the ISO 4217 currency code.

Hence, the role of precious metals as investments, on top of their practical use, drives the demand for them. For thousands of years, precious metals have demanded prices that are much higher than those of common industrial metals, such as nickel (about 36 cents per troy ounce) and copper (about 11 cents per troy ounce). As a matter of fact, there have been significant increases in the prices of precious metals at the turn of the Twenty-First century. This has encouraged many enterprises to go into precious metal recycling.