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.
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/cm³ |
| Liquid density at m.p. |
19.77 g/cm³ |
| 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/(mol·K) |
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 nΩ·m |
|
Thermal conductivity |
(300 K) 71.6 W/(m·K) |
|
Thermal expansion |
(25 °C) 8.8 µm/(m·K) |
|
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% |
6.5×1011
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 Darién (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
Sèvres,
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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