Editing Period 5 element (section)

==d-block elements==

===Yttrium===
{{main|Yttrium}}
'''Yttrium''' is a [[chemical element]] with symbol '''Y''' and [[atomic number]] 39. It is a silvery-metallic [[transition metal]] chemically similar to the [[lanthanide]]s and it has often been classified as a "[[rare earth element]]".<ref name="IUPAC">{{cite book
 |author=IUPAC contributors
 |title=Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005
 |editor=N G Connelly |editor2=T Damhus |editor3=R M Hartshorn |editor4=A T Hutton
 |page=51
 |year=2005
 |isbn=0-85404-438-8
 |url=http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf
 |access-date=2007-12-17
 |publisher=RSC Publishing
 |url-status=dead
 |archive-url=https://web.archive.org/web/20090304204436/http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf
 |archive-date=2009-03-04
}}</ref> Yttrium is almost always found combined with the lanthanides in [[rare earth mineral]]s and is never found in nature as a free element. Its only stable [[isotope]], <sup>89</sup>Y, is also its only naturally occurring isotope.

In 1787, [[Carl Axel Arrhenius]] found a new mineral near [[Ytterby]] in Sweden and named it ''[[gadolinite|ytterbite]]'', after the village. [[Johan Gadolin]] discovered yttrium's oxide in Arrhenius' sample in 1789,<ref name="Krogt">[[Yttrium#Krogt|Van der Krogt 2005]]</ref> and [[Anders Gustaf Ekeberg]] named the new oxide ''[[yttria]]''. Elemental yttrium was first isolated in 1828 by [[Friedrich Wöhler]].<ref name="CRC2008">{{Cite book|author = CRC contributors|editor = Lide, David R.|chapter = Yttrium
|year = 2007–2008|title = CRC Handbook of Chemistry and Physics|volume = 4
|page = 41|location = New York|publisher = [[CRC Press]]|isbn = 978-0-8493-0488-0}}</ref>

The most important use of yttrium is in making [[phosphor]]s, such as the red ones used in television set [[cathode-ray tube]] (CRT) displays and in [[LED]]s.<ref name="Cotton">{{cite book|title=Encyclopedia of Inorganic Chemistry|first=Simon A. |last=Cotton| doi= 10.1002/0470862106.ia211 |date= 2006-03-15|chapter=Scandium, Yttrium & the Lanthanides: Inorganic & Coordination Chemistry|isbn=0-470-86078-2}}</ref> Other uses include the production of [[electrode]]s, [[electrolyte]]s, [[electronic filters]], [[laser]]s and [[superconductor]]s; various medical applications; and as [[Trace element|traces]] in various materials to enhance their properties. Yttrium has no known biological role, and exposure to yttrium compounds can cause lung disease in humans.<ref name="osha">{{cite web|author = OSHA contributors|url = http://www.osha.gov/SLTC/healthguidelines/yttriumandcompounds/recognition.html|title = Occupational Safety and Health Guideline for Yttrium and Compounds|access-date = 2008-08-03|publisher = United States Occupational Safety and Health Administration|date = 2007-01-11|url-status = dead|archive-url = https://web.archive.org/web/20130302060936/http://www.osha.gov/SLTC/healthguidelines/yttriumandcompounds/recognition.html|archive-date = 2013-03-02}} (public domain text)</ref>

===Zirconium===

{{main|Zirconium}}

'''Zirconium''' is a [[chemical element]] with the symbol '''Zr''' and [[atomic number]] 40. The name of zirconium is taken from the mineral ''[[zircon]]''.  Its atomic mass is 91.224. It is a lustrous, gray-white, strong [[transition metal]] that resembles [[titanium]]. Zirconium is mainly used as a [[refractory]] and [[opacifier]], although minor amounts are used as alloying agent for its strong resistance to corrosion. Zirconium is obtained mainly from the mineral [[zircon]], which is the most important form of zirconium in use.

Zirconium forms a variety of [[inorganic chemistry|inorganic]] and [[organometallic compounds]] such as [[zirconium dioxide]] and [[zirconocene dichloride]], respectively. Five [[isotope]]s occur naturally, three of which are stable. Zirconium compounds have no biological role.

===Niobium===
{{main|Niobium}}

'''Niobium''', or '''columbium''', is a [[chemical element]] with the symbol '''Nb''' and [[atomic number]] 41. It is a soft, grey, [[ductile]] [[transition metal]], which is often found in the [[pyrochlore]] mineral, the main commercial source for niobium, and [[columbite]]. The name comes from [[Greek mythology]]: ''[[Niobe]]'', daughter of ''[[Tantalus]]''.

Niobium has physical and chemical properties similar to those of the element [[tantalum]], and the two are therefore difficult to distinguish. The English chemist [[Charles Hatchett]] reported a new element similar to tantalum in 1801, and named it columbium. In 1809, the English chemist [[William Hyde Wollaston]] wrongly concluded that tantalum and columbium were identical. The German chemist [[Heinrich Rose]] determined in 1846 that tantalum ores contain a second element, which he named niobium. In 1864 and 1865, a series of scientific findings clarified that niobium and columbium were the same element (as distinguished from tantalum), and for a century both names were used interchangeably. The name of the element was officially adopted as niobium in 1949.

It was not until the early 20th century that niobium was first used commercially. [[Brazil]] is the leading producer of niobium and [[ferroniobium]], an [[alloy]] of niobium and iron. Niobium is used mostly in alloys, the largest part in special [[steel]] such as that used in gas [[Pipeline transport|pipelines]]. Although alloys contain only a maximum of 0.1%, that small percentage of niobium improves the strength of the steel. The temperature stability of niobium-containing [[superalloy]]s is important for its use in [[jet engine|jet]] and [[rocket engine]]s. Niobium is used in various [[Superconductivity|superconducting]] materials. These [[Type-II superconductor|superconducting alloys]], also containing [[titanium]] and [[tin]], are widely used in the [[superconducting magnet]]s of [[Magnetic resonance imaging|MRI scanners]]. Other applications of niobium include its use in welding, nuclear industries, electronics, optics, [[numismatics]] and jewelry. In the last two applications, niobium's low toxicity and ability to be colored by [[Anodizing|anodization]] are particular advantages.

===Molybdenum===
{{main| Molybdenum}}

'''Molybdenum''' is a [[Group 6 element|Group 6]] [[chemical element]] with the symbol '''Mo''' and [[atomic number]] 42. The name is from Neo-Latin ''Molybdaenum'', from [[Ancient Greek]] {{lang|grc|Μόλυβδος}} {{lang|grc-Latn|molybdos}}, meaning ''lead'', itself proposed as a [[loanword]] from [[Anatolian languages|Anatolian]] [[Luvian language|Luvian]] and [[Lydian language|Lydian]] languages,<ref name="melchert">{{cite web|author=Melchert, Craig |url=http://www.unc.edu/~melchert/molybdos.pdf |title=Greek mólybdos as a Loanword from Lydian |publisher=[[University of North Carolina]] at [[Chapel Hill, North Carolina|Chapel Hill]] |access-date=2011-04-23 |url-status=dead |archive-url=https://web.archive.org/web/20081012125202/http://www.unc.edu/~melchert/molybdos.pdf |archive-date=2008-10-12 }}</ref> since its ores were confused with lead ores.<ref name="CRCdescription">{{Cite book|contribution = Molybdenum|year = 1994|title = CRC Handbook of Chemistry and Physics|editor-last = Lide|editor-first = David R.|volume = 4|page = 18|publisher = Chemical Rubber Publishing Company|isbn=0-8493-0474-1|author = editor-in-chief David R. Lide.}}</ref> The free element, which is a silvery [[metal]], has the [[List of elements by melting point|sixth-highest]] [[melting point]] of any element. It readily forms hard, stable [[carbide]]s, and for this reason it is often used in high-strength [[steel]] alloys. Molybdenum does not occur as a [[Native metal|free metal]] on Earth, but rather in various [[oxidation state]]s in minerals. Industrially, molybdenum [[Chemical compound|compounds]] are used in [[high-pressure]] and high-temperature applications, as [[pigments]] and [[Catalysis|catalysts]].

Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by [[Carl Wilhelm Scheele]]. The metal was first isolated in 1781 by [[Peter Jacob Hjelm]].

Most molybdenum compounds have low [[solubility]] in water, but the molybdate ion MoO<sub>4</sub><sup>2−</sup> is soluble and forms when molybdenum-containing minerals are in contact with [[oxygen]] and water.

===Technetium===
{{main|Technetium}}

'''Technetium''' is the [[chemical element]] with [[atomic number]] 43 and symbol '''Tc'''. It is the lowest [[atomic number]] element without any [[stable isotope]]s; every form of it is [[radioactive]]. Nearly all technetium is produced synthetically and only minute amounts are found in nature. Naturally occurring technetium occurs as a spontaneous [[fission product]] in [[uranium ore]] or by [[neutron capture]] in [[molybdenum]] ores. The chemical properties of this silvery gray, crystalline [[transition metal]] are intermediate between [[rhenium]] and [[manganese]].

Many of technetium's properties were predicted by [[Dmitri Mendeleev]] before the element was discovered. Mendeleev noted a gap in his [[periodic table]] and gave the undiscovered element the provisional name ''[[Mendeleev's predicted elements|ekamanganese]]'' (''Em''). In 1937 technetium (specifically the [[technetium-97]] isotope) became the first predominantly artificial element to be produced, hence its name (from the [[Greek language|Greek]] {{lang|el|τεχνητός}}, meaning "artificial").

Its short-lived [[gamma ray]]-emitting [[nuclear isomer]]—[[technetium-99m]]—is used in [[nuclear medicine]] for a wide variety of diagnostic tests. Technetium-99 is used as a gamma ray-free source of [[beta particle]]s. Long-lived [[isotopes of technetium|technetium isotopes]] produced commercially are by-products of [[nuclear fission|fission]] of [[uranium-235]] in [[nuclear reactor]]s and are extracted from [[nuclear fuel cycle|nuclear fuel rods]]. Because no isotope of technetium has a [[half-life]] longer than 4.2&nbsp;million years ([[technetium-98]]), its detection in [[red giant]]s in 1952, which are billions of years old, helped bolster the theory that stars can produce heavier elements.

===Ruthenium===
{{main|Ruthenium}}

'''Ruthenium''' is a [[chemical element]] with symbol '''Ru''' and [[atomic number]] 44. It is a rare [[transition metal]] belonging to the [[platinum group]] of the [[periodic table]]. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The [[Russia]]n scientist [[Karl Ernst Claus]] discovered the element in 1844 and named it after [[Ruthenia]], the Latin word for [[Etymology of Rus and derivatives|Rus']]. Ruthenium usually occurs as a minor component of [[platinum]] ores and its annual production is only about 12 [[tonne]]s worldwide. Most ruthenium is used for wear-resistant electrical contacts and the production of thick-film resistors. A minor application of ruthenium is its use in some platinum [[alloy]]s.

===Rhodium===

{{main|Rhodium}}

'''Rhodium''' is a [[chemical element]] that is a rare, silvery-white, hard, and [[chemically inert]] [[transition metal]] and a member of the [[platinum group]]. It has the [[chemical symbol]] '''Rh''' and [[atomic number]] 45. It is composed of only one [[isotope]], <sup>103</sup>Rh. Naturally occurring rhodium is found as the free metal, alloyed with similar metals, and never as a chemical compound. It is one of the rarest [[precious metal]]s and one of the most costly ([[gold]] has since taken over the top spot of cost per ounce).

Rhodium is a so-called [[noble metal]], resistant to corrosion, found in platinum or nickel ores together with the other members of the [[platinum group]] metals. It was [[discovery of the chemical elements|discovered]] in 1803 by [[William Hyde Wollaston]] in one such ore, and named for the rose color of one of its chlorine compounds, produced after it reacted with the powerful acid mixture [[aqua regia]].

The element's major use (about 80% of world rhodium production) is as one of the [[catalyst]]s in the [[Catalytic converter#Three-way|three-way catalytic converters]] of automobiles. Because rhodium metal is inert against corrosion and most aggressive chemicals, and because of its rarity, rhodium is usually [[alloy]]ed with [[platinum]] or [[palladium]] and applied in high-temperature and corrosion-resistive coatings. [[White gold]] is often plated with a thin rhodium layer to improve its optical impression while [[sterling silver]] is often rhodium plated for tarnish resistance.

Rhodium detectors are used in [[Nuclear reactor technology|nuclear reactors]] to measure the [[Neutron detection|neutron flux level]].

===Palladium===

{{main|Palladium}}

'''Palladium''' is a [[chemical element]] with the [[chemical symbol]] '''Pd''' and an [[atomic number]] of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by [[William Hyde Wollaston]]. He named it after the [[2 Pallas|asteroid Pallas]], which was itself named after the [[epithet]] of the [[Greek mythology|Greek]] goddess [[Athena]], acquired by her when she slew [[Pallas (daughter of Triton)|Pallas]]. Palladium, [[platinum]], [[rhodium]], [[ruthenium]], [[iridium]] and [[osmium]] form a group of elements referred to as the [[platinum group]] metals (PGMs). These have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.

The unique properties of palladium and other platinum group metals account for their widespread use. A quarter of all goods manufactured today either contain PGMs or have a significant part in their manufacturing process played by PGMs.<ref>{{cite web|publisher=International Platinum Group Metals Association|title=Palladium|url=http://www.ipa-news.com/pgm/index.htm|url-status=dead|archive-url=https://web.archive.org/web/20100420034649/http://www.ipa-news.com/pgm/index.htm|archive-date=2010-04-20}}</ref> Over half of the supply of palladium and its [[Congener (chemistry)|congener]] platinum goes into [[catalytic converter]]s, which convert up to 90% of harmful gases from auto exhaust ([[hydrocarbons]], [[carbon monoxide]], and [[nitrogen dioxide]]) into less-harmful substances ([[nitrogen]], [[carbon dioxide]] and [[water vapor]]). Palladium is also used in electronics, [[dentistry]], [[medicine]], hydrogen purification, chemical applications, and groundwater treatment. Palladium plays a key role in the technology used for [[fuel cell]]s, which combine hydrogen and oxygen to produce electricity, heat, and water.

[[Ore]] [[Deposit (geology)|deposits]] of palladium and other PGMs are rare, and the most extensive deposits have been found in the norite belt of the [[Bushveld Igneous Complex]] covering the [[Transvaal Basin]] in South Africa, the [[Stillwater igneous complex|Stillwater Complex]] in [[Montana]], United States, the [[Thunder Bay District]] of [[Ontario]], Canada, and the [[Norilsk|Norilsk Complex]] in Russia. [[Recycling]] is also a source of palladium, mostly from scrapped catalytic converters. The numerous applications and limited supply sources of palladium result in the metal attracting considerable [[Palladium as an investment|investment]] interest.

===Silver===
{{main|Silver}}

'''Silver''' is a metallic [[chemical element]] with the [[chemical symbol]] '''Ag''' ({{langx|la|argentum}}, from the [[Indo-European root]] ''*arg-'' for "grey" or "shining") and [[atomic number]] 47. A soft, white, lustrous [[transition metal]], it has the highest [[electrical conductivity]] of any element and the highest [[thermal conductivity]] of any metal. The metal occurs naturally in its pure, free form (native silver), as an [[alloy]] with [[gold]] and other metals, and in minerals such as [[argentite]] and [[chlorargyrite]]. Most silver is produced as a byproduct of [[copper]], [[gold]], [[lead]], and [[zinc]] [[refining]].

Silver has long been valued as a [[precious metal]], and it is used to make ornaments, [[jewelry]], high-value tableware, utensils (hence the term ''[[Silver (household)|silverware]]''), and currency [[coin]]s. Today, silver metal is also used in electrical contacts and [[Electrical conductor|conductors]], in mirrors and in [[catalysis]] of chemical reactions. Its compounds are used in [[photographic film]], and dilute [[silver nitrate]] solutions and other silver compounds are used as [[disinfectant]]s and microbiocides. While many medical [[antimicrobial]] uses of silver have been supplanted by [[antibiotics]], further research into clinical potential continues.

===Cadmium===
{{main|Cadmium}}
'''Cadmium''' is a [[chemical element]] with the symbol '''Cd''' and [[atomic number]] 48. This soft, bluish-white metal is chemically similar to the two other stable metals in [[group 12 element|group 12]], [[zinc]] and [[mercury (element)|mercury]]. Like zinc, it prefers [[oxidation state]] +2 in most of its compounds and like mercury it shows a low melting point compared to [[transition metal]]s. Cadmium and its [[Congener (chemistry)|congeners]] are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in the Earth's crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by [[Friedrich Stromeyer|Stromeyer]] and [[Karl Samuel Leberecht Hermann|Hermann]], both in Germany, as an impurity in [[zinc carbonate]].

Cadmium occurs as a minor component in most zinc ores and therefore is a byproduct of zinc production. It was used for a long time as a [[pigment]] and for corrosion resistant plating on [[steel]] while cadmium compounds were used to stabilize [[plastic]]. With the exception of its use in [[nickel–cadmium battery|nickel–cadmium batteries]] and [[cadmium telluride]] [[solar panel]]s, the use of cadmium is generally decreasing. These declines have been due to competing technologies, cadmium's [[toxicity]] in certain forms and concentration and resulting regulations.<ref name="ReferenceA">{{cite book|chapter = Cadmium|title = Kirk-Othmer Encyclopedia of Chemical Technology|edition = 4th|place=New York|publisher = John Wiley & Sons|year=1994|volume= 5}}</ref>