Platinum, << PLAT uh nuhm, >> is a precious, silver-white metal that is even more valuable than gold. It ranks as one of the heaviest chemical elements, weighing more than 21 times as much as an equal volume of water.
Many characteristics of platinum make it valuable. It can be drawn into fine wire or hammered into thin sheets. Only gold and silver are easier to shape. Unlike iron and many other metals, platinum does not oxidize (react with oxygen) easily. It does not corrode or tarnish because it does not combine readily with oxygen or sulfur compounds in the air. Strong acids that dissolve most metals do not attack platinum, but it will dissolve in a mixture of nitric and hydrochloric acid called aqua regia (see Aqua regia ). Platinum melts at a relatively high temperature, around 1770 °C.
Platinum’s chemical symbol is Pt. Its atomic number (the number of protons in its nucleus) is 78. Its relative atomic mass is 195.078. An element’s relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of carbon 12, the most abundant form of carbon.
Chemists classify platinum as a transition metal . For information on the position of platinum on the periodic table, see the article Periodic table .
Platinum usually occurs in nature in the native (pure metal) state because it does not form compounds easily. However, it is occasionally found in compounds with arsenic or sulfur. Grains of native platinum typically contain traces of other metals. These metals-iridium, osmium, palladium, rhodium, and ruthenium-are known, together with platinum, as the platinum group metals. Grains of native platinum often occur in beds of gold-bearing sand, and miners have called platinum white gold. Grains that bear platinum-group metals may also contain small amounts of chromium, copper, iron, and titanium.
Uses.
Because platinum is so unreactive and has such a high melting point, manufacturers use it to make containers for chemical reactions. It also finds use in surgical instruments. Platinum has become a favorite material for making expensive jewelry. Its strength, hardness, color, and freedom from tarnish make it ideal for delicate gem settings.
Platinum serves as an effective catalyst, a substance that speeds up chemical reactions. Automobile manufacturers use it in pollution-reducing devices called catalytic converters. The platinum helps decompose harmful exhaust pollutants, such as nitrogen oxides, into harmless substances, such as nitrogen and oxygen (see Catalytic converter ). The petroleum industry uses platinum as a catalyst to convert oil into gasoline that has a high octane number, a measure of how smoothly fuel burns in an engine (see Petroleum (Refining petroleum) ). Platinum can also serve as a catalyst in the production of acetic acid and nitric acid (see Catalysis ).
Platinum forms alloys (metallic combinations) with most other metals. The most useful alloys combine platinum with one or more of the following metals: cobalt, iridium, osmium, palladium, rhodium, and ruthenium. An alloy of platinum and iridium makes an ideal surface for fine engravings. This alloy is also used to make contact points for electrical equipment, tips for fountain pens, and measurement standards, objects that define basic units of measure.
Platinum forms compounds with arsenic, phosphorus, and silicon. In some photographic prints, platinum compounds take the place of silver. Other platinum compounds serve as drugs used to treat cancer. They bind to DNA (deoxyribonucleic acid, the genetic material) in cancer cells, preventing them from reproducing.
History.
In the 1500’s, conquistadors (Spanish conquerors) found silvery grains of an unknown metal mixed with gold deposits in Latin America. At the time, there were no known means for melting the grains to shape the metal, so miners discarded the grains as worthless. In 1557, the Italian-born French scholar Julius Scaliger first described the metal in writing. In 1748, the Spanish noble and scientist Antonio de Ulloa named the metal platina, a form of the Spanish word for silver. William Brownrigg, an English physician, recognized platinum as a new element in 1750. By 1803, the English chemist William Wollaston had produced the first pure sample of platinum.
Today, South Africa is the leading producer of platinum. Other producers include Canada, Colombia, Russia, and the United States.
