Editing Period 6 element (section)

==d-block elements==

===Lutetium===
{{main|Lutetium}}
'''Lutetium''' ({{IPAc-en|l|juː|ˈ|t|iː|ʃ|i|ə|m}} {{respell|lew|TEE|shee-əm}}) is a [[chemical element]] with the symbol '''Lu''' and [[atomic number]] 71. It is the last element in the [[lanthanide]] series, which, along with the [[lanthanide contraction]], explains several important properties of lutetium, such as it having the highest hardness or density among lanthanides. Unlike other lanthanides, which lie in the [[f-block]] of the [[periodic table]], this element lies in the [[d-block]]; however, [[lanthanum]] is sometimes placed on the d-block lanthanide position. Chemically, lutetium is a typical lanthanide: its only common oxidation state is +3, seen in its oxide, halides and other compounds. In an aqueous solution, like compounds of other late lanthanides, soluble lutetium compounds form a complex with nine water molecules.

Lutetium was independently discovered in 1907 by French scientist [[Georges Urbain]], Austrian mineralogist Baron [[Carl Auer von Welsbach]], and American chemist [[Charles James (chemist)|Charles James]]. All of these men found lutetium as an impurity in the mineral [[ytterbia]], which was previously thought to consist entirely of ytterbium. The dispute on the priority of the discovery occurred shortly after, with Urbain and von Welsbach accusing each other of publishing results influenced by the published research of the other; the naming honor went to Urbain as he published his results earlier. He chose the name lutecium for the new element but in 1949 the spelling of element 71 was changed to lutetium. In 1909, the priority was finally granted to Urbain and his names were adopted as official ones; however, the name cassiopeium (or later cassiopium) for element 71 proposed by von Welsbach was used by many German scientists until the 1950s. Like other lanthanides, lutetium is one of the elements that traditionally were included in the classification "[[rare-earth element|rare earth]]s."

Lutetium is rare and expensive; consequently, it has few specific uses. For example, a [[radioactive isotope]] lutetium-176 is used in [[nuclear technology]] to determine the age of [[meteorite]]s. Lutetium usually occurs in association with the element [[yttrium]] and is sometimes used in metal [[alloy]]s and as a [[catalyst]] in various chemical reactions. <sup>177</sup>Lu-[[DOTA-TATE]] is used for radionuclide therapy (see [[Nuclear medicine]]) on neuroendocrine tumours.
<!------------<ref>{{cite news| url=http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html|title =IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (online draft of an updated version of the "''Red Book''" IR 3-6)| date =2004| accessdate = 2009-06-06}}</ref>----------------->

===Hafnium===
{{main|Hafnium}}
'''Hafnium''' is a [[chemical element]] with the [[element symbol|symbol]] '''Hf''' and [[atomic number]] 72. A [[lustre (mineralogy)|lustrous]], silvery gray, [[tetravalence|tetravalent]] [[transition metal]], hafnium chemically resembles [[zirconium]] and is found in zirconium [[mineral]]s. Its existence was [[Mendeleev's predicted elements|predicted by Dmitri Mendeleev]] in 1869. Hafnium was the penultimate [[stable isotope]] element to be discovered ([[rhenium]] was identified two years later). Hafnium is named for ''Hafnia'', the [[Latin]] name for "[[Copenhagen]]", where it was discovered.

Hafnium is used in filaments and electrodes.  Some [[semiconductor]] fabrication processes use its oxide for [[integrated circuits]] at 45&nbsp;nm and smaller feature lengths. Some [[superalloy]]s used for special applications contain hafnium in combination with [[niobium]], [[titanium]], or [[tungsten]].

Hafnium's large [[neutron capture]] cross-section makes it a good material for [[neutron]] absorption in [[control rod]]s in [[nuclear power plant]]s, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.

===Tantalum===
{{main|Tantalum}}
'''Tantalum''' is a [[chemical element]] with the symbol '''Ta''' and [[atomic number]] 73. Previously known as ''tantalium'', the name comes from ''[[Tantalus]]'', a character from Greek mythology.<ref>[[Euripides]], ''[[Orestes (play)|Orestes]]''</ref> Tantalum is a rare, hard, blue-gray, [[lustre (mineralogy)|lustrous]] [[transition metal]] that is highly corrosion resistant. It is part of the [[refractory metals]] group, which are widely used as minor component in alloys. The chemical inertness of tantalum makes it a valuable substance for laboratory equipment and a substitute for [[platinum]], but its main use today is in [[tantalum capacitor]]s in [[electronics|electronic]] equipment such as [[mobile phone]]s, [[DVD player]]s, [[video game systems]] and [[Personal computer|computers]].
Tantalum, always together with the chemically similar [[niobium]], occurs in the [[mineral]]s [[tantalite]], [[columbite]] and [[coltan]] (a mix of columbite and tantalite).

===Tungsten===
{{main|Tungsten}}
'''Tungsten''', also known as '''wolfram''', is a [[chemical element]] with the chemical symbol '''W''' and [[atomic number]] 74. The word ''tungsten'' comes from the Swedish language ''tung sten'' directly translatable to ''heavy stone'',<ref>{{OED|Tungsten}}</ref> though the name is ''volfram'' in Swedish to distinguish it from [[Scheelite]], in Swedish alternatively named ''tungsten''.

A hard, rare [[metal]] under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as a metal in 1783. Its important [[ore]]s include [[wolframite]] and [[scheelite]]. The [[free element]] is remarkable for its robustness, especially the fact that it has the highest [[melting point]] of all the non-[[alloy]]ed metals and the second highest of all the elements after [[carbon]]. Also remarkable is its high density of 19.3 times that of water, comparable to that of [[uranium]] and [[gold]], and much higher (about 1.7 times) than that of [[lead]].<ref name="daintith">{{cite book |last=Daintith |first=John |title=Facts on File Dictionary of Chemistry |edition=4th |location=New York |publisher=Checkmark Books |year=2005 |isbn=978-0-8160-5649-1 }}</ref> Tungsten with minor amounts of impurities is often [[brittle]]<ref>{{cite book |title=Tungsten: properties, chemistry, technology of the element, alloys, and chemical compounds|first = Erik|last = Lassner|author2=Schubert, Wolf-Dieter | publisher = Springer|year = 1999|isbn = 978-0-306-45053-2|chapter-url = https://books.google.com/books?id=foLRISkt9gcC&pg=PA20|chapter = low temperature brittleness|pages = 20–21}}</ref> and [[hardness|hard]], making it difficult to [[metalworking|work]]. However, very pure tungsten, though still hard, is more [[ductility|ductile]], and can be cut with a hard-steel [[hacksaw]].<ref name="albert">{{cite book |last=Stwertka |first=Albert |title=A Guide to the elements |edition=2nd |location=New York |publisher=Oxford University Press |year=2002 |isbn=978-0-19-515026-1 }}</ref>

The unalloyed elemental form is used mainly in electrical applications. Tungsten's many alloys have numerous applications, most notably in incandescent [[light bulb]] filaments, [[X-ray tube]]s (as both the filament and target), electrodes in [[TIG welding]], and [[superalloys]]. Tungsten's hardness and high [[density]] give it military applications in penetrating [[projectile]]s. Tungsten compounds are most often used industrially as [[catalyst]]s.

Tungsten is the only metal from the third [[Transition metal|transition]] series that is known to occur in [[biomolecule]]s, where it is used in a few species of bacteria. It is the heaviest element known to be used by any living organism. Tungsten interferes with [[molybdenum]] and [[copper]]  metabolism, and is somewhat toxic to animal life.<ref>{{cite journal
|title = The active sites of molybdenum- and tungsten-containing enzymes
|author1=McMaster, J.  |author2=Enemark, John H
 |name-list-style=amp |journal = Current Opinion in Chemical Biology
|volume = 2
|issue = 2
|pages = 201–207
|year = 1998
|doi = 10.1016/S1367-5931(98)80061-6
|pmid = 9667924}}</ref><ref>{{cite journal
|title = Molybdenum and tungsten in biology
|author = Hille, Russ
|journal = Trends in Biochemical Sciences
|volume = 27
|issue = 7
|pages = 360–367
|year = 2002
|doi = 10.1016/S0968-0004(02)02107-2
|pmid = 12114025}}</ref>

===Rhenium===
{{main|Rhenium}}
'''Rhenium''' is a [[chemical element]] with the symbol '''Re''' and [[atomic number]] 75. It is a silvery-white, heavy, third-row [[transition metal]] in [[group 7 element|group 7]] of the [[periodic table]]. With an ''estimated'' average concentration of 1 [[Parts-per notation|part per billion]] (ppb), rhenium is one of the rarest elements in the [[Earth's crust]]. The free element has the [[List of elements by melting point|third-highest]] [[melting point]] and highest boiling point of any element. Rhenium resembles [[manganese]] chemically and is obtained as a [[by-product]] of [[molybdenum]] and [[copper]] ore's extraction and refinement. Rhenium shows in its compounds a wide variety of [[oxidation state]]s ranging from −1 to +7.

Discovered in 1925, rhenium was the last [[stable element]] to be discovered. It was named after the river [[Rhine]] in Europe.

[[Nickel]]-based [[superalloys]] of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of [[jet engine]]s, these alloys  contain up to 6% rhenium, making jet engine construction the largest single use for the element, with the chemical industry's catalytic uses being next-most important. Because of the low availability relative to demand, rhenium is among the most expensive of metals, with an average price of approximately US$4,575 per [[kilogram]] (US$142.30 per troy ounce) as of August 2011; it is also of critical strategic military importance, for its use in high performance military jet and rocket engines.<ref>{{cite web |url=http://www.metalprices.com/FreeSite/metals/re/re.asp |title=Rhenium |work=MetalPrices.com |access-date=February 2, 2012 |archive-date=January 15, 2012 |archive-url=https://web.archive.org/web/20120115004912/http://www.metalprices.com/FreeSite/metals/re/re.asp |url-status=dead }}</ref>

===Osmium===
{{main|Osmium}}
'''Osmium''' is a [[chemical element]] with the symbol '''Os''' and [[atomic number]] 76. It is a hard, brittle, blue-gray or blue-black [[transition metal]] in the [[platinum family]] and is the densest naturally occurring element, with a [[density]] of  {{val|22.59|ul=g/cm3}} (slightly greater than that of [[iridium]] and twice that of [[lead]]). It is found in nature as an alloy, mostly in platinum ores; its [[alloy]]s with [[platinum]], [[iridium]], and other platinum group metals are employed in [[fountain pen]] tips, electrical contacts, and other applications where extreme durability and hardness are needed.<ref>Hammond "Osmium", C. R., p. 4-25 in {{RubberBible86th}}</ref>

===Iridium===
{{main|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 group|platinum family]], iridium is the second-[[density|densest]] element (after [[osmium]]) and is the most [[corrosion]]-resistant metal, even at temperatures as high as 2000&nbsp;°C. Although only certain molten salts and [[halogen]]s are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable.

Iridium was discovered in 1803 among insoluble impurities in natural [[platinum]]. [[Smithson Tennant]], the primary discoverer, named the iridium for the goddess [[Iris (mythology)|Iris]], personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is [[Abundance of elements in Earth's crust|one of the rarest elements]] in the [[Crust (geology)#Earth's crust|Earth's crust]], with annual production and consumption of only three [[tonne]]s. {{chem|191|Ir}} and {{chem|193|Ir}} are the only two naturally occurring [[isotope]]s of iridium as well as the only [[stable isotope]]s; the latter is the more abundant of the two.

The most important iridium compounds in use are the salts and acids it forms with [[chlorine]], though iridium also forms a number of [[organometallic compound]]s used in industrial [[catalysis]], and in research. Iridium metal is employed when high corrosion resistance at high temperatures is needed, as in high-end [[spark plug]]s, [[crucible]]s for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the [[chloralkali process]]. Iridium radioisotopes are used in some [[radioisotope thermoelectric generator]]s.

Iridium is found in meteorites with an abundance much higher than its average abundance in the Earth's crust. For this reason the unusually high abundance of iridium in the clay layer at the [[Cretaceous–Paleogene boundary]] gave rise to the [[Alvarez hypothesis]] that the impact of a massive extraterrestrial object caused the extinction of dinosaurs and many other species 66&nbsp;million years ago. It is thought that the total amount of iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum group metals, the high density and [[Goldschmidt classification#Siderophile elements|tendency]] of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten.

===Platinum===
{{main|Platinum}}
'''Platinum''' is a [[chemical element]] with the [[chemical symbol]] '''Pt''' and an [[atomic number]] of 78.

Its name is derived from the Spanish term ''platina'', which is literally translated into "little silver".<ref>[http://www.britannica.com/EBchecked/topic/464081/platinum-Pt "platinum (Pt)."] Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. 24 April 2012</ref><ref>{{OEtymD|platinum}}</ref><!--source for "platina del Pinto"<ref>{{cite book|last=Woods|first=Ian|title=The Elements: Platinum|publisher=Benchmark Books|year=2004|series=The Elements|isbn=978-0-7614-1550-3}}</ref>--> It is a [[density|dense]], [[malleability|malleable]], [[ductility|ductile]], [[precious metal|precious]], gray-white [[transition metal]].

Platinum has six naturally occurring [[isotopes of platinum|isotopes]]. It is one of the [[Abundance of elements in Earth's crust|rarest elements in the Earth's crust]] and has an average abundance of approximately 5&nbsp;μg/kg. It is the [[Reactivity series|least reactive metal]]. It occurs in some [[nickel]] and [[copper]] ores along with some native deposits, mostly in South Africa, which accounts for 80% of the world production.

As a member of the [[platinum group]] of elements, as well as of the [[group 10 element|group 10]] of the [[periodic table of elements]], platinum is generally non-reactive. It exhibits a remarkable resistance to corrosion, even at high temperatures, and as such is considered a [[noble metal]]. As a result, platinum is often found chemically uncombined as native platinum. Because it occurs naturally in the [[alluvium|alluvial sands]] of various rivers, it was first used by [[pre-Columbian]] South American natives to produce artifacts. It was referenced in European writings as early as 16th century, but it was not until [[Antonio de Ulloa]] published a report on a new metal of [[Colombia]]n origin in 1748 that it became investigated by scientists.

Platinum is used in [[catalytic converter]]s, laboratory equipment, [[electrical contacts]] and [[electrode]]s, [[platinum-resistance thermometer]]s, [[dentistry]] equipment, and jewelry. Because only a few hundred tonnes are produced annually, it is a scarce material, and is highly valuable. Being a [[heavy metals|heavy metal]], it leads to health issues upon exposure to its salts, but due to its corrosion resistance, it is not as toxic as some metals.<ref>{{cite web|url= http://www.euro.who.int/__data/assets/pdf_file/0015/123081/AQG2ndEd_6_11Platinum.PDF|title= Platinum&#124;|access-date= 2012-08-28|archive-date= 2012-10-18|archive-url= https://web.archive.org/web/20121018173735/http://www.euro.who.int/__data/assets/pdf_file/0015/123081/AQG2ndEd_6_11Platinum.PDF|url-status= dead}}</ref> Its compounds, most notably [[cisplatin]], are applied in [[chemotherapy]] against certain types of cancer.<ref>{{cite journal | pmid = 20593091 | year = 2010 | last1 = Wheate | first1 = N. J. | last2 = Walker | first2 = S. | last3 = Craig | first3 = G. E. | last4 = Oun | first4 = R. | title = The status of platinum anticancer drugs in the clinic and in clinical trials | volume = 39 | issue = 35 | pages = 8113–27 | doi = 10.1039/C0DT00292E | journal = Dalton Transactions| url = https://ses.library.usyd.edu.au/bitstream/2123/9269/2/41%20Dalton%20perspective.pdf | hdl = 2123/14271 | hdl-access = free }}</ref>

===Gold===
{{main|Gold}}
'''Gold''' is a dense, soft, shiny, malleable and ductile metal.  It is a [[chemical element]] with the symbol '''Au''' and [[atomic number]] 79.

Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a [[transition metal]] and a [[group 11 element]]. It is one of the least reactive chemical elements solid under standard conditions. The metal therefore occurs often in free elemental (native) form, as [[gold nugget|nuggets]] or grains in rocks, in [[vein (geology)|veins]] and in [[alluvial deposit]]s. Less commonly, it occurs in minerals as gold compounds, usually with [[tellurium]].

Gold resists attacks by individual acids, but it can be dissolved by the [[aqua regia]] (nitro-[[hydrochloric acid]]), so named because it dissolves gold. Gold also dissolves in alkaline solutions of [[cyanide]], which have been used in mining. Gold dissolves in [[mercury (element)|mercury]], forming [[amalgam (chemistry)|amalgam]] alloys. Gold is insoluble in [[nitric acid]], which dissolves [[silver]] and [[base metal]]s, a property that has long been used to confirm the presence of gold in items, giving rise to the term ''the [[acid test (gold)|acid test]].''

Gold has been a valuable and highly sought-after [[precious metal]] for [[coin]]age, jewelry, and other arts since long before the beginning of [[recorded history]]. [[Gold standard]]s have been a common basis for [[monetary policy|monetary policies]] throughout human history,{{Citation needed|date=April 2012}} later being supplanted by [[fiat currency]] starting in the 1930s. The last [[gold certificate]] and [[gold coin]] currencies were issued in the U.S. in 1932. In Europe, most countries left the gold standard with the start of [[World War I]] in 1914 and, with huge war debts, failed to return to gold as a medium of exchange.

A total of 165,000 [[tonne]]s of gold have been mined in human history, as of 2009.<ref name="World Gold Council FAQ">[http://www.gold.org/faq/answer/76/how_much_gold_has_been_mined/ World Gold Council FAQ]. www.gold.org</ref> This is roughly equivalent to 5.3 billion [[troy ounce]]s or, in terms of volume, about 8500 m<sup>3</sup>, or a [[cube]] 20.4 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.<ref name='oil-price.com-worlds-gold-consumption 2011'>{{cite news|first = Andy |last = Soos|title = Gold Mining Boom Increasing Mercury Pollution Risk|date = 2011-01-06|publisher = Oilprice.com|url = http://oilprice.com/Metals/Gold/Gold-Mining-Boom-Increasing-Mercury-Pollution-Risk.html|work = Advanced Media Solutions, Inc.|access-date = 2011-03-26}}</ref>

Besides its widespread monetary and symbolic functions, gold has many practical uses in [[dentistry]], [[electronics]], and other fields. Its high [[malleability]], [[ductility]], resistance to corrosion and most other chemical reactions, and conductivity of electricity led to many uses of gold, including [[electric wiring]], colored-glass production and even [[gold leaf]] eating.

It has been claimed that most of the Earth's gold lies at its core, the metal's high density having made it sink there in the planet's youth.  Virtually all of the gold that mankind has discovered is considered to have been deposited later by [[meteorites]] which contained the element.  This supposedly explains why, in prehistory, gold appeared as nuggets on the earth's surface.<ref>{{cite news| url=https://www.bbc.co.uk/news/science-environment-14827624 | work=BBC News | title=Meteorites delivered gold to Earth | date=2011-09-08}}</ref><ref>{{Cite web | url=https://www.sciencedaily.com/releases/2011/09/110907132044.htm |title = Where does all Earth's gold come from? Precious metals the result of meteorite bombardment, rock analysis finds}}</ref><ref>{{Cite journal |last1=Kirk |first1=Jason |last2=Ruiz |first2=Joaquin |last3=Chesley |first3=John |last4=Titley |first4=Spencer |date=2003 |title=The Origin of Gold in South Africa |url=http://www.sas.rochester.edu/ees/ees119/reading2.pdf |journal=American Scientist |volume=91 |issue=6 |pages=534–541 |doi=10.1511/2003.38.534 |issn=0003-0996}}</ref><ref>{{cite news| url=http://www.huffingtonpost.com/2011/09/10/meteor-shower-gold_n_955448.html | work=Huffington Post | title=Meteor Shower Rained Gold On Ancient Earth | date=2011-09-10}}</ref><ref>{{Cite journal |doi = 10.1038/nature10399|pmid = 21901010|title = The tungsten isotopic composition of the Earth's mantle before the terminal bombardment|journal = Nature|volume = 477|issue = 7363|pages = 195–198|year = 2011|last1 = Willbold|first1 = Matthias|last2 = Elliott|first2 = Tim|last3 = Moorbath|first3 = Stephen|bibcode = 2011Natur.477..195W|s2cid = 4419046}}</ref>

===Mercury===
{{main|Mercury (element)}}
'''Mercury''' is a [[chemical element]] with the symbol '''Hg''' and [[atomic number]] 80. It is also known as '''quicksilver'''<!--ref>{{cite web|url=http://dictionary.reference.com/browse/quicksilver|title=quicksilver definition |access-date=13 October 2008|publisher=Dictionary.com Unabridged (v 1.1)}}</ref---> or '''hydrargyrum''' ( < Greek "[[Wiktionary:en:hydr-|hydr-]]" ''water'' and "[[Wiktionary:en:άργυρος|argyros]]" ''silver''). A heavy, silvery [[d-block]] element, mercury is the only metal that is liquid at [[standard conditions for temperature and pressure]]; the only other element that is liquid under these conditions is [[bromine]], though metals such as [[caesium]], [[francium]], [[gallium]], and [[rubidium]] melt just above room temperature. With a [[freezing point]] of −38.83&nbsp;°C and [[boiling point]] of 356.73&nbsp;°C, mercury has one of the narrowest ranges of its liquid state of any metal.<ref>{{cite web|url=http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/why-is-mercury-liquid.shtml| title=Why is mercury a liquid at STP?| access-date=May 1, 2007| publisher=General Chemistry Online at Frostburg State University| author=Senese, F}}</ref><ref name="Norrby">{{cite journal|author=Norrby, L.J.|title=Why is mercury liquid? Or, why do relativistic effects not get into chemistry textbooks?| journal= Journal of Chemical Education|volume=68|issue=2|page=110 |year=1991|doi=10.1021/ed068p110|bibcode=1991JChEd..68..110N}}</ref><ref>{{RubberBible86th|pages=4.125–4.126}}</ref>

Mercury occurs in deposits throughout the world mostly as [[cinnabar]] ([[mercuric sulfide]]). The red pigment [[vermilion]] is mostly obtained by reduction from cinnabar. Cinnabar is highly toxic by ingestion or inhalation of the dust. [[Mercury poisoning]] can also result from exposure to water-soluble forms of mercury (such as [[mercuric chloride]] or [[methylmercury]]), inhalation of mercury vapor, or eating seafood contaminated with mercury.

Mercury is used in [[thermometer]]s, [[barometer]]s, [[manometer]]s, [[sphygmomanometer]]s, [[float valve]]s, [[mercury switch]]es, and other devices though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favor of [[ethanol|alcohol]]-filled, [[galinstan]]-filled, digital, or [[thermistor]]-based instruments. It remains in use in scientific research applications and in [[amalgam (dentistry)|amalgam]] material for [[dental restoration]]. It is used in lighting: electricity passed through mercury vapor in a phosphor tube produces short-wave [[ultraviolet light]] which then causes the phosphor to [[fluoresce]], making visible light.