Science Fair Project Encyclopedia
|Name, Symbol, Number||Platinum, Pt, 78|
|Chemical series||transition metals|
|Group, Period, Block||10 , 6, d|
|Density, Hardness||21.45 Mg/m³, 3.5|
|Atomic weight||195.078 g/mol|
|Atomic radius (calc.)||135 (177) pm|
|Covalent radius||128 pm|
|van der Waals radius||175 pm|
|e- 's per energy level||2, 8, 18, 32, 17, 1|
|Oxidation states (Oxide)||2, 4 (mildly basic)|
|Crystal structure||Cubic face centered|
|State of matter||solid (paramagnetic)|
|Melting point||2041.4 K (3214.9 °F)|
|Boiling point||4098 K (6917 °F)|
|Molar volume||9.09 cm³/mol|
|Heat of vaporization||510 kJ/mol|
|Heat of fusion||19.6 kJ/mol|
|Vapor pressure||0.0312 Pa at 2045 K|
|Speed of sound||2680 m/s at 25 °C|
|Electronegativity||2.28 (Pauling scale)|
|Specific heat capacity||130 J/(kg·K)|
|Electrical conductivity||9.66 MS/m|
|Thermal conductivity||71.6 W/(m·K)|
|1st ionization potential||870 kJ/mol|
|2nd ionization potential||1791 kJ/mol|
|Most stable isotopes|
|SI units & STP are used except where noted.|
Platinum is a chemical element in the periodic table that has the symbol Pt and atomic number 78. A heavy, malleable, ductile, precious, gray-white transition metal, platinum is resistant to corrosion and occurs in some nickel and copper ores along with some native deposits. Platinum is used in jewelry, laboratory equipment, electrical contacts, dentistry, and anti-pollution devices in automobiles.
The metal is a beautiful silvery-white when pure, and malleable and ductile. The metal is corrosion-resistant. The catalytic properties of the six platinum family metals are outstanding (a mixture of hydrogen and oxygen explodes in the presence of platinum). Platinum's wear- and tarnish-resistance characteristics are well-suited for making fine jewelry.
Other distinctive properties include resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications. Platinum does not oxidize in air at any temperature but can be corroded by cyanides, halogens, sulfur, and caustic alkalis. This metal is insoluble in hydrochloric and nitric acid but does dissolve in the mixture known as aqua regia (forming chloroplatinic acid ). Common oxidation states of platinum include +2, +3, and +4.
Naturally-occurring platinum and platinum-rich alloys have been known for a long time. Though the metal was used by pre-Columbian Indians, the first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger (1484-1558) as a description of a mysterious metal found in Central American mines between Darién (Panama) and Mexico ("up until now impossible to melt by any of the Spanish arts").
The Spaniards named the metal "platino," or little silver, when they first encountered it in Colombia. They regarded platinum as an unwanted impurity in the silver they were mining, and often discarded it.
Platinum was discovered by astronomer Antonio de Ulloa and Don Jorge Juan y Santacilia (1713-1773), both appointed by King Philip V to join a geographical expedition in Peru that lasted from 1735 to 1745. Among other things, Ulloa observed the platina del pinto, the unworkable metal found with gold in New Granada (Colombia). British privateers intercepted Ulloa's ship on the return voyage. Though he was well-treated in England, and even made a member of the Royal Society he was prevented from publishing a reference to the unknown metal until 1748. Before that could happen Charles Wood independently isolated the element in 1741.
The alchemical symbol for platinum (shown below) was made by joining the symbols of silver and gold.
Platinum is now considered more precious than gold, so that a platinum award is better than a golden one. The price of platinum changes along with its availability, but it normally costs about twice as much as gold.
The standard definition of a metre for a long time was based on the distance between two marks on a bar of a platinum-iridium alloy housed at the Bureau International des Poids et Mesures in Sevres, France. A platinum-iridium cylinder serves to this day as the standard of the kilogram and is housed in the same facility as the metre bar. Platinum is also used in the definition of the Standard hydrogen electrode.
Platinum is often found in a native state and the ore sperrylite (platinum arsenide, PtAs2) is a major source of the metal. A naturally occurring platinum/iridium alloy is platiniridium and this metal is also found in the mineral cooperite (platinum sulfide, PtS).
Platinum is produced commercially as a by-product of nickel ore processing. The huge quantities of nickel ore processed makes up for the fact that platinum makes up only two parts per million of the ore.
The Anglo Platinum Group ( http://www.angloplatinum.com ) is the world's leading primary producer of platinum group metals from its South African mines. It mines, processes, refines and markets platinum group metals as its main products.
Naturally occurring platinum is composed of five stable isotopes and one radioisotope, Pt-190, which has a very long half-life (over 6 billion years or 190 Ps). There are also many other radioisotopes with the most stable being Pt-193 with a half-life of 50 years.
This metal doesn't normally cause health problems due to its unreactive nature but all compounds of platinum should be considered to be highly toxic. Platinum compounds rarely occur in nature.
- The Platinum Group Metals Database
- A balanced historical account of the sequence of discoveries of platinum; illustrated.
- WebElements.com - Platinum
- EnvironmentalChemistry.com - Platinum
- Platinum Metals Review E-Journal
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