Platinum is a chemical element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, with the chemical symbol Chemical symbols may also be modified by the use of superscripts or subscripts to show a specific isotope of an atom. Additionally superscripts may be used to indicate the ionization or oxidation state of an element Pt and an atomic number In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element. In an atom of neutral charge, the atomic number is also equal to the number of of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River."^[1] It is in Group 10 of the periodic table of elements The periodiс table of the chemical elements is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table. A dense The density of a material is defined as its mass per unit volume. The symbol of density is ρ . In some countries (for instance, in the United States), density is also defined as its weight per unit volume . The density of a substance is the reciprocal of its specific volume, a representation commonly used in thermodynamics, malleable Ductility is a mechanical property that describes the extent in which solid materials can be plastically deformed without fracture, ductile Ductility is a mechanical property that describes the extent in which solid materials can be plastically deformed without fracture, precious A precious metal is a rare, naturally occurring metallic chemical element of high economic value, which is not radioactive . Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals. Historically, precious metals were important as currency,, gray-white transition metal The name transition comes from their position in the periodic table of elements. In each of the four periods in which they occur, these elements represent the successive addition of electrons to the d atomic orbitals of the atoms. In this way, the transition metals represent the transition between group 2 elements and group 13 elements, platinum is resistant to corrosion and occurs in some nickel Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements that exist around room temperature, the other three being iron, cobalt and gadolinium and copper Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly exposed surface has a pinkish or peachy color. It is used as a thermal conductor, an electrical conductor, a building material, and a ores along with some native deposits. Platinum is used in jewelry, laboratory equipment, electrical Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning and static electricity, but in addition, less familiar concepts, such as the electromagnetic field and electromagnetic induction contacts and electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit . The word was coined by the scientist Michael Faraday from the Greek words elektron (meaning amber, from which the word electricity is derived) and hodos, a way, platinum resistance thermometers Resistance thermometers, also called resistance temperature detectors or resistive thermal devices , are temperature sensors that exploit the predictable change in electrical resistance of some materials with changing temperature. As they are almost invariably made of platinum, they are often called platinum resistance thermometers (PRTs). They, dentistry Dentistry, which is a part of stomatology, is the branch of medicine that is involved in the evaluation, diagnosis, prevention, and surgical or non-surgical treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely equipment, and catalytic converters A catalytic converter is a device used to reduce the toxicity of emissions from an internal combustion engine. First widely introduced on series-production automobiles in the U.S. market for the 1975 model year to comply with tightening EPA regulations on auto exhaust, catalytic converters are still most commonly used in motor vehicle exhaust. Some of its compounds are used in chemotherapy for cancer patients.^[2]

Characteristics

Physical and chemical

As a pure metal, platinum is silvery-white in appearance, lustrous, ductile, and malleable.^[3] It does not oxidize at any temperature, although it is corroded by halogens The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The artificially created element 117, provisionally referred to by the systematic name ununseptium, may also be a halogen, cyanides A cyanide is any chemical compound that contains the cyano group , which consists of a carbon atom triple-bonded to a nitrogen atom. Inorganic cyanides are generally salts of the anion CN−. Of the many kinds of cyanide compounds, some are gases; others are solids or liquids. Those that can release the cyanide ion CN− are highly toxic, sulfur Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a bright yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals. It is an essential element for life and is found in, and caustic alkalis. Platinum is insoluble in hydrochloric Hydrochloric acid is the solution of hydrogen chloride (H and nitric acid Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming nitric acid. Fuming nitric acid is characterized as white fuming nitric acid and red fuming nitric acid, depending on the amount of nitrogen dioxide present, but dissolves in aqua regia Aqua regia or aqua regis is a highly corrosive, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and concentrated hydrochloric acid, usually in a volumetric ratio of 1:3 respectively. It was named so because it can dissolve the so-called "royal metals," to form chloroplatinic acid, H₂PtCl₆.^[4]

Platinum's resistance to wear and tarnish is well suited for making fine jewelry Jewellery or jewelry (see American and British English spelling differences) is a form of personal adornment, manifesting itself as necklaces, rings, brooches, earrings and bracelets. Jewellery may be made from any material, usually gemstones, precious metals or shells. Factors affecting the choice of materials include cultural differences and the. The metal has an excellent resistance to corrosion Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Formation of an oxide of iron due to oxidation of the iron atoms in solid solution is a and high temperatures and has stable electrical properties. All of these characteristics have been exploited for industrial applications.^[5]

The most common oxidation states In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by integers, which can be positive, negative, or zero of platinum are +2, and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) species. As is expected, tetracoordinate platinum(II) compounds tend to adopt a square planar The square planar molecular geometry in chemistry describes the stereochemistry that is adopted by certain chemical compounds. As the name suggests, molecules of this geometry have their atoms positioned at the corners of a square on the same plane about a central atom geometry. While elemental platinum is generally unreactive, it dissolves in aqua regia Aqua regia or aqua regis is a highly corrosive, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and concentrated hydrochloric acid, usually in a volumetric ratio of 1:3 respectively. It was named so because it can dissolve the so-called "royal metals," to give soluble hexachloroplatinic acid Chloroplatinic acid or hexachloroplatinic acid is the chemical compound usually found as the hexahydrate with the formula H2PtCl6·6. This is one of the most readily available soluble compounds of platinum. It is rarely obtained in the pure state. The commercial product is the oxonium salt of the hexachloroplatinate(IV) anion. Therefore, the ("H₂PtCl₆", formally (H₃O)₂PtCl₆·nH₂O ):^[6]

Pt + 4 HNO₃ + 6 HCl → H₂PtCl₆ + 4 NO₂ + 4 H₂O

As a soft acid, platinum has a great affinity for sulfur, such as on DMSO Dimethyl sulfoxide is the organosulfur compound with the formula (CH3)2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water. It has a distinctive property of penetrating the skin very readily, so that one may taste it; numerous DMSO complexes have been reported and care should be taken in the choice of reaction solvent.^[7]

Several barium platinides have been synthesized, in which platinum exhibits negative oxidation states ranging from −1 to −2. These include BaPt, Ba₃Pt₂, and Ba₂Pt.^[8] Caesium platinide, Cs₂Pt, has been shown to contain Pt²⁻ anions.^[9] Platinum is also shown to exhibit negative oxidation states at surfaces reduced electrochemically.^[10] The negative oxidation states exhibited by platinum, which are unusual for metallic elements, are believed to be due to the relativistic stabilization of the 6s orbitals.^[9]

Isotopes

Platinum has six naturally occurring isotopes Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. In a corresponding manner, isotopes differ in mass number (or number of nucleons) but never in atomic number. The number of protons (the atomic number) is the same because that is what characterizes a chemical element. For example,: ¹⁹⁰Pt, ¹⁹²Pt, ¹⁹⁴Pt, ¹⁹⁵Pt, ¹⁹⁶Pt, and ¹⁹⁸Pt. The most abundant In chemistry, natural abundance refers to the abundance isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average) of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an isotope varies from planet to planet but remains relatively constant in time of these is ¹⁹⁵Pt, comprising 33.83% of all platinum. ¹⁹⁰Pt is the least abundant at only .01%. Of the naturally occurring isotopes, only ¹⁹⁰Pt is unstable, though it decays with a half-life of 6.5 × 10¹¹ years. ¹⁹⁸Pt undergoes alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle, and thereby transforms into an atom with a mass number 4 less and atomic number 2 less. For example:, but because its half-life Half-life is the period of time it takes for a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay is estimated as being greater than 3.2 × 10¹⁴ years, it is considered stable. Platinum also has 31 synthetic isotopes ranging in atomic mass from 166 to 202, making the total number of known isotopes 37. The least stable of these is ¹⁶⁶Pt with a half-life of 300 µs, while the most stable is ¹⁹³Pt with a half-life of 50 years. Most of platinum's isotopes decay by some combination of beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus (β⁻), while in the case of a positron emission as beta plus (β+). Kinetic energy of beta particles has continuous spectrum ranging from 0 to maximal available energy (Q), which and alpha decay. ¹⁸⁸Pt, ¹⁹¹Pt, and ¹⁹³Pt decay primarily by electron capture Electron capture is a decay mode for isotopes that will occur when there are too many protons in the nucleus of an atom and insufficient energy to emit a positron; however, it continues to be a viable decay mode for radioactive isotopes that can decay by positron emission. If the energy difference between the parent atom and the daughter atom is. ¹⁹⁰Pt and ¹⁹⁸Pt have double beta decay In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted. In the process of beta minus decay, unstable nuclei decay by converting a neutron in the nucleus to a proton and emitting an electron and an electronic antineutrino. In order for beta decay to be possible, the paths.^[11]

Occurrence

Platinum is an extremely rare metal,^[12] occurring as only 0.003 ppb Parts-per notation is used, especially in science and engineering, to denote relative proportions in measured quantities; particularly in low-value proportions at the parts-per-million (ppm) 10–6, parts-per-billion (ppb) 10–9, and parts-per-trillion (ppt) 10–12 level. Since parts-per notations are quantity-per-quantity measures, they are in the Earth Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[note 6] or by its Latin name, Terra.[note 7]'s crust In geology, a crust is the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle. The crusts of Earth, our Moon, Mercury, Venus, Mars, Io, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantles. It is sometimes mistaken for silver (Ag).

Platinum is often found chemically uncombined as native platinum and alloyed An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history. Alloys usually have different properties from those of the with iridium Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second densest element (after osmium) and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and as platiniridium. Most often the native platinum is found in secondary deposits; platinum is combined with the other platinum group metals in alluvial Alluvium is loose, unconsolidated (not cemented together into a solid rock), soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material deposits. The alluvial deposits used by pre-Columbian The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences on the American continents, spanning the time of the original settlement in the Upper Paleolithic period to European colonization during the Early Modern period people in the Chocó Department Chocó is a department of Colombia known for its large Afro-Colombian population. It is in the west of the country, and is the only Colombian department to have coastlines on both the Pacific Ocean and the Atlantic Ocean. It also has all of Colombia's border with Panama. Its capital is Quibdó, Colombia Colombia (pronounced /kəˈlʌmbiə/ ), officially the Republic of Colombia (Spanish: República de Colombia, pronounced [reˈpuβlika ðe koˈlombja] ( listen)), is a constitutional republic in northwestern South America. Colombia is bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; are still a source for platinum group metals. Another large alluvial deposit was found in the Ural Mountains The Ural Mountains are a mountain range that runs approximately from north to south through western Russia, from the coast of the Arctic Ocean to the Ural River and northwestern Kazakhstan. Their eastern side is usually considered the natural boundary between Europe and Asia. The mountains lie within the Ural geographical region and significantly, Russia, which is still mined.

In nickel Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements that exist around room temperature, the other three being iron, cobalt and gadolinium and copper Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly exposed surface has a pinkish or peachy color. It is used as a thermal conductor, an electrical conductor, a building material, and a deposits platinum group metals occur as sulfides A sulfide is an anion of sulfur in its lowest oxidation number of −2. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors (i.e., (Pt,Pd)S)), tellurides (i.e., PtBiTe), antimonides Antimonides are compounds of antimony with more electropositive elements. The antimonide ion is Sb3− (PdSb), and arsenides (i.e., PtAs₂), and as end alloys with nickel or copper. 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, Gauteng, South Africa.^[13]

In 1865 chromites were identified in the Bushveld region of South Africa followed by the discovery of platinum in 1906.^[14] The largest known primary reserves are in the Bushveld complex in South Africa.^[15] The large copper–nickel deposits near Norilsk in Russia, and the Sudbury Basin, Canada, are the two other large deposits. In the Sudbury Basin the huge quantities of nickel ore processed makes up for the fact that platinum is present as only 0.5 ppm in the ore. Smaller reserves can be found in the United States,^[15] for example in the Absaroka Range in Montana.^[16] In 2005, South Africa was the top producer of platinum with an almost 80% share followed by Russia and Canada.^[17]

Platinum exists in higher abundances on the Moon and in meteorites. Correspondingly, platinum is found in slightly higher abundances at sites of bolide impact on the Earth that are associated with resulting post-impact volcanism, and can be mined economically; the Sudbury Basin is one such example.^[18]

Production

Platinum together with the rest of the platinum metals is obtained commercially as a by-product from nickel and copper mining and processing. During electrorefining of copper, noble metals such as silver, gold and the platinum group metals as well as selenium and tellurium settle to the bottom of the cell as anode mud, which forms the starting point for the extraction of the platinum group metals.^[19][20]

If pure platinum is found in placer deposits or other ores, it is isolated from them by various methods of subtracting impurities. Because platinum is significantly denser than many of its impurities, the lighter impurities can be removed by simply floating them away in a water bath. Platinum is also non-magnetic, while nickel and iron are both magnetic. These two impurities are thus removed by running an electromagnet over the mixture. Because platinum has a higher melting point than most other substances, many impurities can be burned or melted away without melting the platinum. Finally, platinum is resistant to hydrochloric and sulfuric acids, while other substances are readily attacked by them. Metal impurities can be removed by stirring the mixture in either of the two acids and recovering the remaining platinum.^[21]

One suitable method for purification for the raw platinum, which contains platinum, gold, and the other platinum group metals, is to process it with aqua regia, in which palladium, gold and platinum are dissolved, while osmium, iridium, ruthenium and rhodium stay unreacted. The gold is precipitated by the addition of iron(III) chloride and after filtering off the gold, the platinum is precipitated by the addition of ammonium chloride as ammonium chloroplatinate. Ammonium chloroplatinate can be converted to the metal by heating.^[22]

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