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Platinum

Platinum Ring

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Platinum is a chemical element in the periodic table that has the symbol Pt and atomic number 78. A heavy, malleable, ductile, precious, grey-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 jewellery, laboratory equipment, electrical contacts, dentistry, and automobile emissions control devices.

Platinum

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Notable characteristics

The metal appears silvery-white when pure, and firm. 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). For this catalytic property, platinum is used in catalytic converters, incorporated in automobile exhaust systems, as well as tips of spark plugs.

78 iridium ← platinum → gold
General
Name, Symbol, Number platinum, Pt, 78
Chemical series transition metals
Group, Period, Block 10, 6, d
Appearance greyish white
Atomic mass 195.084(9) g/mol
Electron configuration [Xe] 4f14 5d9 6s1
Electrons per shell 2, 8, 18, 32, 17, 1
Physical properties
Phase solid
Density (near r.t.) 21.45 g/cm
Liquid density at m.p. 19.77 g/cm
Melting point 2041.4 K
(1768.3 C, 3214.9 F)
Boiling point 4098 K
(3825 C, 6917 F)
Heat of fusion 22.17 kJ/mol
Heat of vaporization 469 kJ/mol
Heat capacity (25 C) 25.86 J/(molK)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2330 (2550) 2815 3143 3556 4094
Atomic properties
Crystal structure cubic face centered
Oxidation states 2, 3, 4
(mildly basic oxide)
Electro negativity 2.28 (Pauling scale)
Ionization energies 1st: 870 kJ/mol
2nd: 1791 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.) 177 pm
Covalent radius 128 pm
Van der Waals radius 175 pm
Miscellaneous
Magnetic ordering paramagnetic
Electrical resistivity (20 C) 105 nΩm
Thermal conductivity (300 K) 71.6 W/(mK)
Thermal expansion (25 C) 8.8 m/(mK)
Speed of sound (thin rod) (r.t.) 2800 m/s
Young's modulus 168 GPa
Shear modulus 61 GPa
Bulk modulus 230 GPa
Poisson ratio 0.38
Mohs hardness 3.5
Vickers hardness 549 MPa
Brinell hardness 392 MPa
CAS registry number 7440-06-4
Notable isotopes
Main article: Isotopes of platinum
iso NA half-life DM DE (MeV) DP
190Pt 0.01% 6.51011 y α 3.18 186Os
191Pt syn 2.96 d ε  ? 191Ir
192Pt 0.79% Pt is stable with 114 neutrons
193mPt syn 4.33 d IT 0.1355e 193Pt
193Pt syn 50 y ε  ? 193Ir
194Pt 32.9% Pt is stable with 116 neutrons
195mPt syn 4.02 d IT 0.1297e 195Pt
195Pt 33.8% Pt is stable with 117 neutrons
196Pt 25.3% Pt is stable with 118 neutrons
197mPt syn 1.59 h IT 0.3465 197Pt
197Pt syn 19.8913 h β- 0.719 197Au
198Pt 7.2% Pt is stable with 120 neutrons

Platinum's wear- and tarnish-resistance characteristics are well suited for making fine jewelry. Platinum is more precious than gold. The price of platinum changes along with its availability, but it normally costs about twice as much as gold. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.

Platinum possesses remarkable resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications. Platinum does not oxidise 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.

Applications

  • catalyst utilized in the catalytic converter, an optional component of the gasoline-fuelled automobile exhaust system (see "Notable characteristics" in this article),
  • certain platinum-containing compounds are capable of intercalating into DNA and are chemotherapeutic agents owing to this capability. For example, cisplatin, carboplatin and oxaliplatin belong to this class of drugs,
  • platinum resistance thermometers,
  • electrodes for use in electrolysis.

History

Naturally-occurring platinum and platinum-rich alloys have been known for a long time. Though the metal was used by pre-Columbian Native Americans, 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 Darin (Panama) and Mexico ("up until now impossible to melt by any of the Spanish arts").

The Spaniards named the metal "platina," 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.

The 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 Svres, 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.

Occurrence

Platinum is an extremely rare metal, occurring as only 5 ppb in the Earth's crust.

Platinum is often found free in areas of the Americas and alloyed with iridium as platiniridium. The platinum arsenide, sperrylite (PtAs2), is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Transvaal, South Africa.

Platinum, often accompanied by small amounts of other platinum family metals, occurs in alluvial placer deposits in the Witwatersrand of South Africa, Colombia, Ontario, the Ural Mountains, and in certain western American states.

Platinum is produced commercially as a by-product of nickel ore processing in the Sudbury deposit. The huge quantities of nickel ore processed makes up for the fact that platinum is present as only 0.5 ppm in the ore.

Isotopes

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.

Precautions

This metal doesn't normally cause health problems due to its unreactive nature. Platinum compounds rarely occur in nature. Certain platinum complexes (cis-platin) have been used in chemotherapy, as they have very good anti-tumour activity, though they do unfortunately cause cumulative irreversible kidney damage.

Rarity and Colour

Platinum's rarity as a metal has caused advertisers to associate it with exclusivity and wealth. "Platinum" credit cards have greater privileges than do "gold" ones. "Platinum awards" are the highest possible, ranking above gold, silver and bronze. For example, a musical album that has sold more than 1,000,000 copies, will be credited as "platinum". And some products, such as blenders and vehicles, with a silvery-white colour are identified as "platinum" (a higher certification of "Diamond" does exist, however). Platinum is considered a precious metal, although its use as such is much more rare than the use of gold or silver. The frame of the Crown of Queen Elizabeth the Queen Mother, manufactured for her Coronation as Consort of King George VI is made of platinum. It was the first British Crown to be made of that metal. Due to its rarity, platinum is a highly priced metal, more so than gold or silver.

References

  • Los Alamos National Laboratory - Platinum
  • Nuclides and Isotopes Fourteenth Edition: Chart of the Nuclides, General Electric Company, 1989
  • Jefferson Lab - The Element Platinum

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