Platinum (Pt)

• Element Symbol: Pt
• Atomic Number: 78
• Atomic Mass: 195.078
• Group # in Periodic Table: 10
• Group Name: Transition metals
• Period in Periodic Table: 6
• Block of Periodic Table: d-block
• Discovered by: pre-Columbian peoples (ancient); Antonio de Ulloa (1735)

Platinum is a transition metal whose symbol is Pt and whose atomic number 78. It is a dense, malleable, gray-white precious metal. A precious metal is one that is rare and of high economic value. Chemically, the precious metals are less reactive than most other elements. They are also referred to as the noble metals. Like the other precious metals, platinum is chemically unreactive. In fact platinum is the least reactive of any metal, so much so that it resists corrosion (rusting) even at high temperatures. This noble metal is obviously a member of the platinum group. It is the last one in the group and its namesake. The other five transition metals are ruthenium, rhodium, palladium, osmium, and iridium. Due to its remarkable physical and chemical properties, platinum has many commercial, scientific, and biological applications.

Platinum was discovered by pre-Columbian Americans near modern-day Esmeraldas, Ecuador. They used platinum metal to produce artifacts of a white gold–platinum alloy. The platinum was not the pure element; rather, it was a naturally occurring mixture of platinum and small amounts of palladium, rhodium, and iridium. It was the Spanish conquistadors who named platinum after the Spanish word platina, which means "little silver."

The first European reference to platinum occurred in 1557 in the writings of Julius Caesar Scaliger, an Italian humanist. He described it as a strange metal found in the mines between Panama and Mexico that no Spanish fire could melt. Nearly two hundred year later, in 1735, the Spanish explorer and astronomer Antonio de Ulloa was sent on the French Geodesic Mission to what is now Ecuador, where he wrote the first known scientific description of the metal. For this reason, Ulloa is often credited as the first European to discover platinum.

It was not until 1783 that a method for producing workable platinum was discovered. The discoverer was Pierre-François Chabaneau, a French chemist. However, the method was not perfect because the quality of the platinum metal was not consistent from batch to batch due to impurities caused by other undiscovered metals. It took until the early nineteenth century (around 1803) for a reliable method of producing pure platinum to be devised. The scientist who discovered this effective extraction method was English chemist William H. Wollaston, who just happened to work in the same lab as Smithson Tennant. It was Tennant who discovered osmium and iridium. In fact these two London chemists often worked together on the platinum-group metals.

Physical Properties

Pure platinum metal is lustrous (shiny), ductile (can be stretched into wire), malleable (can be flattened out), and moderately hard, with a Mohs hardness of 4–4.5. It is silver-white in color. Platinum is more ductile than gold, silver, or copper, thus making it the most ductile of the noble metals. However, it is not the most malleable metal, as that honor goes to gold. Platinum is slightly less dense than osmium, with a density of 21.45 grams per cubic centimeter (g/cm³) at room temperature. Both its boiling point (3825 °C) and its melting point (1768.3 °C) are relatively high. Since it is a metal, its standard state at 298 kelvins (K) is solid. Due to these remarkable physical properties, platinum has many useful applications.

Chemical Properties

Because it is a noble metal, platinum is not very reactive chemically. In fact it is the least reactive of all the metals. It has four oxidation states, +1 to +4, with +2 and +4 being the most common. Platinum(II) will only react slowly with oxygen at extremely high temperatures. In this oxidation state, platinum will react vigorously with fluorine at 500 °C to form platinum tetrafluoride (PtF₄). Platinum does not dissolve when placed in nitric acid or hydrochloric acid alone, but it does dissolve when placed in hot aqua regia, which is a combination of hydrochloric and nitric acids. The result is chloroplatinic acid (H₂PtCl₆).

Platinum has six naturally occurring isotopes, with mass numbers 190, 192, 194, 195, 196, and 198. The most abundant is platinum-195, which makes up 33.83 percent of all platinum. The least abundant, platinum-190, makes up only 0.01 percent of all platinum. Of these six isotopes, five are stable; only platinum-190 is considered to be slightly unstable, with a half-life of 6.5 × 10¹¹ years. Due to these notable chemical properties, platinum is often used in several different applications.

Applications

Platinum is an extremely rare, precious metal with a concentration of only 0.05 parts per million in Earth’s crust. It is often found chemically uncombined as pure platinum or as an alloy with other group members or iron. Platinum mines are found all over the world, in places such as Colombia, Russia, Canada, Alaska, and South Africa. Platinum and the other platinum group metals are obtained commercially as a by-product of nickel and copper mining and processing.

Due to its noteworthy physical and chemical properties, platinum metal and its alloys have numerous commercial, chemical, and biological applications. Commercially, platinum is primarily used in vehicle emissions control devices and jewelry making because it is so hard, dense, and resistant to rusting. Chemically, platinum has been used as catalyst since the early nineteenth century. Specifically, it was used to catalyze hydrogen ignition reactions. This is important because platinum is still used to today to make catalytic converters for automobiles. These converters are what contain the hydrogen ignition reactions that convert fuel into energy in car engines. Biologically, platinum-containing compounds are used in a number of different chemotherapy treatments. Three specific ones are cisplatin, carboplatin, and oxaliplatin. These platinum compounds are used to treat solid tumors as well as neurologic and blood cancers in combination with other chemical compounds. Overall, it can be said that platinum is one of the most useful elements in the periodic table.

Bibliography

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Kaye & Laby Tables of Physical & Chemical Constants. Natl. Physical Laboratory, 2015. Web. 25 Sept 2015.

"Platinum Element Facts." Chemicool. Chemicool.com. 17 Oct. 2012. Web. 7 Aug. 2015.