Editing Period 5 element

{{Short description|Fifth row of the periodic table}}
{{Periodic table (micro)| title=Period 5 in the [[periodic table]] | mark=Rb,Sr,Y,Zr,Nb,Mo,Tc,Ru,Rh,Pd,Ag,Cd,In,Sn,Sb,Te,I,Xe}}
{{Sidebar periodic table|expanded=structure }}
A '''period 5 element''' is one of the [[chemical element]]s in the fifth row (or [[Period (periodic table)|period]]) of the [[Periodic table|periodic table of the chemical elements]]. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with [[rubidium]] and ending with [[xenon]]. As a rule, period 5 elements fill their 5s [[electron shell|shells]] first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as [[rhodium]].

==Physical properties==

This period contains [[technetium]], one of the two elements until [[lead]] that has no stable isotopes (along with [[promethium]]), as well as [[molybdenum]] and [[iodine]], two of the heaviest elements with a known biological role.<ref>{{cite web|url=http://www.3rd1000.com/elements/Iodine.htm |title=Iodine |publisher=3rd1000.com |access-date=2012-08-13}}</ref><ref>{{cite web|url=http://www.webelements.com/molybdenum/biology.html |title=WebElements Periodic Table of the Elements &#124; Molybdenum &#124; biological information |publisher=Webelements.com |access-date=2012-08-13}}</ref> [[Niobium]] has the largest known magnetic penetration depth of all the elements.<ref>{{cite journal|title = A Superconducting Nb<sub>3</sub>Sn Coated Multicell Accelerating Cavity|first = M.|last = Peiniger|author2=Piel, H. |journal = IEEE Transactions on Nuclear Science|date= 1985|volume= 32|issue = 5|doi = 10.1109/TNS.1985.4334443|pages = 3610–3612|bibcode = 1985ITNS...32.3610P |s2cid = 23988671}}</ref> [[Zirconium]] is one of the main components of [[zircon crystals]], currently the oldest known minerals in the Earth's crust. Many later [[transition metals]], such as rhodium, are very commonly used in jewelry as they are very shiny.<ref name="Gray" >{{cite book|last=Gray|first=Theodore|title=The Elements: A Visual Exploration of Every Known Atom in the Universe|year=2009|publisher=Black Dog & Leventhal Publishers|location=New York|isbn=978-1-57912-814-2|url-access=registration|url=https://archive.org/details/elementsvisualex0000gray}}</ref>

This period is known to have a large number of exceptions to the [[Madelung rule]].

==Elements and their properties==
:{| class="wikitable sortable"
! colspan="3" | [[Chemical element]]
! [[Block (periodic table)|Block]]
! [[Electron configuration]]
|-
!&nbsp;
!
!
!
!
|- bgcolor="{{element color|s-block}}"
|| 37  || '''Rb''' || [[Rubidium]] || [[s-block]] || [Kr] 5s<sup>1</sup>
|- bgcolor="{{element color|s-block}}"
|| 38  || '''Sr''' || [[Strontium]] || [[s-block]] || [Kr] 5s<sup>2</sup>
|- bgcolor="{{element color|d-block}}"
|| 39  || '''Y''' || [[Yttrium]] || [[d-block]] || [Kr] 4d<sup>1</sup> 5s<sup>2</sup>
|- bgcolor="{{element color|d-block}}"
|| 40  || '''Zr''' || [[Zirconium]] || [[d-block]] || [Kr] 4d<sup>2</sup> 5s<sup>2</sup>
|- bgcolor="{{element color|d-block}}"
|| 41  || '''Nb''' || [[Niobium]] || [[d-block]] || [Kr] 4d<sup>4</sup> 5s<sup>1</sup> (*)
|- bgcolor="{{element color|d-block}}"
|| 42  || '''Mo''' || [[Molybdenum]] || [[d-block]] || [Kr] 4d<sup>5</sup> 5s<sup>1</sup> (*)
|- bgcolor="{{element color|d-block}}"
|| 43  || '''Tc''' || [[Technetium]] || [[d-block]] || [Kr] 4d<sup>5</sup> 5s<sup>2</sup>
|- bgcolor="{{element color|d-block}}"
|| 44 || '''Ru''' || [[Ruthenium]] || [[d-block]] || [Kr] 4d<sup>7</sup> 5s<sup>1</sup> (*)
|- bgcolor="{{element color|d-block}}"
|| 45 || '''Rh''' || [[Rhodium]] || [[d-block]]|| [Kr] 4d<sup>8</sup> 5s<sup>1</sup> (*)
|- bgcolor="{{element color|d-block}}"
|| 46 || '''Pd''' || [[Palladium]] || [[d-block]] || [Kr] 4d<sup>10</sup> (*)
|- bgcolor="{{element color|d-block}}"
|| 47 || '''Ag''' || [[Silver]] || [[d-block]] || [Kr] 4d<sup>10</sup> 5s<sup>1</sup> (*)
|- bgcolor="{{element color|d-block}}"
|| 48 || '''Cd''' || [[Cadmium]] || [[d-block]] || [Kr] 4d<sup>10</sup> 5s<sup>2</sup>
|- bgcolor="{{element color|p-block}}"
|| 49 || '''In''' || [[Indium]] || [[p-block]] || [Kr] 4d<sup>10</sup> 5s<sup>2</sup> 5p<sup>1</sup>
|- bgcolor="{{element color|p-block}}"
|| 50 || '''Sn''' || [[Tin]] || [[p-block]] || [Kr] 4d<sup>10</sup> 5s<sup>2</sup> 5p<sup>2</sup>
|- bgcolor="{{element color|p-block}}"
|| 51 || '''Sb''' || [[Antimony]] || [[p-block]] || [Kr] 4d<sup>10</sup> 5s<sup>2</sup> 5p<sup>3</sup>
|- bgcolor="{{element color|p-block}}"
|| 52 || '''Te''' || [[Tellurium]] || [[p-block]] || [Kr] 4d<sup>10</sup> 5s<sup>2</sup> 5p<sup>4</sup>
|- bgcolor="{{element color|p-block}}"
|| 53 || '''I''' || [[Iodine]] || [[p-block]] || [Kr] 4d<sup>10</sup> 5s<sup>2</sup> 5p<sup>5</sup>
|- bgcolor="{{element color|p-block}}"
|| 54 || '''Xe''' || [[Xenon]] || [[p-block]] || [Kr] 4d<sup>10</sup> 5s<sup>2</sup> 5p<sup>6</sup>
|}

(*) Exception to the [[Madelung rule]]

== s-block elements ==

=== Rubidium ===
{{main|Rubidium}}

'''Rubidium''' is the first element placed in period 5. It is an [[alkali metal]], the most reactive group in the [[periodic table]], having properties and similarities with both other alkali metals and other period 5 elements. For example, rubidium has 5 electron shells, a property found in all other period 5 elements, whereas its [[electron configuration]]'s ending is similar to all other alkali metals: s<sup>1</sup>.<ref>{{cite web|url=http://environmentalchemistry.com/yogi/periodic/Rb.html |title=Periodic Table of Elements: Rubidium – Rb |publisher=EnvironmentalChemistry.com |date=1995-10-22 |access-date=2012-08-13}}</ref> [[Rubidium]] also follows the trend of increasing [[reactivity (chemistry)|reactivity]] as the atomic number increases in the alkali metals, for it is more reactive than [[potassium]], but less so than [[caesium]]. In addition, both potassium and rubidium yield almost the same hue when [[wikt:ignition|ignited]], so researchers must use different methods to differentiate between these two 1st group elements.<ref>{{cite web|url=http://webmineral.com/help/FlameTest.shtml |title=Flame Tests |publisher=Webmineral.com |access-date=2012-08-13}}</ref> Rubidium is very susceptible to [[Redox|oxidation]] in air, similar to most of the other alkali metals, so it readily transforms into [[rubidium oxide]], a yellow solid with the [[chemical formula]] Rb<sub>2</sub>O.<ref>{{cite web|url=http://www.chemguide.co.uk/inorganic/group1/reacto2.html |title=Reactions of the Group 1 elements with oxygen and chlorine |publisher=Chemguide.co.uk |access-date=2012-08-13}}</ref>

=== Strontium ===
{{main|Strontium}}

'''Strontium''' is the second element placed in the 5th [[Period (periodic table)|period]]. It is an [[alkaline earth metal]], a relatively reactive group, although not nearly as reactive as the [[alkali metals]]. Like rubidium, it has 5 [[electron shells]] or [[energy levels]], and in accordance with the [[Madelung rule]] it has two electrons in its 5s [[Electron shell#Subshells|subshell]]. [[Strontium]] is a soft metal and is extremely [[reactivity (chemistry)|reactive]] upon contact with water. If it comes in contact with water, it will combine with the [[atoms]] of both [[oxygen]] and [[hydrogen]] to form [[strontium hydroxide]] and pure hydrogen gas which quickly [[diffusion|diffuses]] in the [[air]]. In addition, strontium, like rubidium, [[Redox|oxidizes]] in air and turns a [[yellow]] color. When ignited, it will burn with a strong red [[flame]].

==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>

==p-block elements==

===Indium===
{{main|Indium}}
'''Indium''' is a [[chemical element]] with the symbol '''In''' and [[atomic number]] 49. This rare, very soft, malleable and easily [[Fusible alloy|fusible]] [[other metal]] is chemically similar to [[gallium]] and [[thallium]], and shows the intermediate properties between these two. Indium was discovered in 1863 and named for the [[indigo blue]] line in its spectrum that was the first indication of its existence in zinc ores, as a new and unknown element. The metal was first isolated in the following year. Zinc ores continue to be the primary source of indium, where it is found in compound form. Very rarely the element can be found as grains of native (free) metal, but these are not of commercial importance.

Indium's current primary application is to form transparent electrodes from [[indium tin oxide]] in [[liquid crystal display]]s and [[touchscreen]]s, and this use largely determines its global mining production. It is widely used in thin-films to form lubricated layers (during [[World War II]] it was widely used to coat bearings in high-performance [[aircraft]]). It is also used for making particularly low melting point alloys, and is a component in some lead-free solders.

Indium is not known to be used by any organism. In a similar way to aluminium salts, indium(III) ions can be toxic to the kidney when given by injection, but oral indium compounds do not have the chronic toxicity of salts of heavy metals, probably due to poor absorption in basic conditions. Radioactive indium-111 (in very small amounts on a chemical basis) is used in [[nuclear medicine]] tests, as a [[radiotracer]] to follow the movement of labeled proteins and [[indium leukocyte imaging|white blood cells]] in the body.

===Tin===
{{main|Tin}}
'''Tin''' is a [[chemical element]] with the symbol '''Sn''' (for {{langx|la|stannum}}) and [[atomic number]] 50. It is a [[main-group element|main-group metal]] in [[group 14]] of the [[periodic table]]. Tin shows chemical similarity to both neighboring group 14 elements, [[germanium]] and [[lead]] and has two possible [[oxidation state]]s, +2 and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest number of stable [[isotope]]s in the periodic table. Tin is obtained chiefly from the [[mineral]] [[cassiterite]], where it occurs as [[tin dioxide]], SnO<sub>2</sub>.

This silvery, [[malleable]] [[post-transition metal]] is not easily [[oxidation|oxidized]] in air and is used to coat other metals to prevent [[corrosion]]. The first [[alloy]], used in large scale since 3000 BC, was [[bronze]], an alloy of tin and [[copper]]<!--[Anatoly F. Fomenko in his book "History: Fiction or Science",[Chronology 1, pg.70] asserts that Tin metallurgy is more complex than that of Copper and metallic tin had not been known during the Bronze Age. It is possible that some metal of a higher fusibility was manufactured using Copper with some minerals rich in tin content]-->. After 600 BC pure metallic tin was produced. [[Pewter]], which is an alloy of 85–90% tin with the remainder commonly consisting of copper, [[antimony]] and lead, was used for [[tableware]] from the [[Bronze Age]] until the 20th century. In modern times tin is used in many alloys, most notably tin/lead soft [[solder]]s, typically containing 60% or more of tin. Another large application for tin is corrosion-resistant [[tin plating]] of steel. Because of its low toxicity, tin-plated metal is also used for food packaging, giving the name to [[tin can]]s, which are made mostly of steel.

===Antimony===
{{main|Antimony}}
'''Antimony''' ({{langx|la|stibium}}) is a toxic [[chemical element]] with the symbol '''Sb''' and an [[atomic number]] of 51. A lustrous grey [[metalloid]], it is found in nature mainly as the [[sulfide mineral]] [[stibnite]] (Sb<sub>2</sub>S<sub>3</sub>). Antimony compounds have been known since ancient times and were used for cosmetics, metallic antimony was also known but mostly identified as [[lead]].

For some time China has been the largest producer of antimony and its compounds, with most production coming from the [[Xikuangshan Mine]] in [[Hunan]]. Antimony compounds are prominent additives for chlorine and bromine containing [[fire retardant]]s found in many commercial and domestic products. The largest application for metallic antimony is as alloying material for lead and tin. It improves the properties of the alloys which are used as in [[solder]]s, bullets and [[ball bearing]]s. An emerging application is the use of antimony in [[microelectronics]].

===Tellurium===
{{main|Tellurium}}
'''Tellurium''' is a [[chemical element]] that has the symbol '''Te''' and [[atomic number]] 52. A brittle, mildly toxic, rare, silver-white [[metalloid]] which looks similar to [[tin]], tellurium is chemically related to [[selenium]] and [[sulfur]]. It is occasionally found in native form, as elemental crystals. Tellurium is far more common in the universe than on Earth. Its extreme [[abundance of the chemical elements|rarity]] in the Earth's crust, comparable to that of [[platinum]], is partly due to its high atomic number, but also due to its formation of a volatile [[hydride]] which caused the element to be lost to space as a gas during the hot nebular formation of the planet.

Tellurium was discovered in [[Transylvania]] (today part of [[Romania]]) in 1782 by [[Franz-Joseph Müller von Reichenstein]] in a mineral containing tellurium and [[gold]]. [[Martin Heinrich Klaproth]] named the new element in 1798 after the Latin word for "earth", ''tellus''. Gold telluride minerals (responsible for the name of [[Telluride, Colorado]]) are the most notable natural gold compounds. However, they are not a commercially significant source of tellurium itself, which is normally extracted as by-product of [[copper]] and [[lead]] production.

Tellurium is commercially primarily used in [[alloy]]s, foremost in steel and copper to improve machinability. Applications in [[Photovoltaic module|solar panels]] and as a [[semiconductor]] material also consume a considerable fraction of tellurium production.

===Iodine===
{{main|Iodine}}
'''Iodine''' is a [[chemical element]] with the symbol '''I''' and [[atomic number]] 53. The name is from [[Ancient Greek|Greek]] {{lang|grc|ἰοειδής}} ''ioeidēs'', meaning violet or purple, due to the color of elemental iodine vapor.<ref>Online Etymology Dictionary, s.v. [http://www.etymonline.com/index.php?term=iodine ''iodine'']. Retrieved 2012-02-07.</ref>

Iodine and its compounds are primarily used in [[nutrition]], and industrially in the production of [[acetic acid]] and certain polymers. Iodine's relatively high atomic number, low toxicity, and ease of attachment to organic compounds have made it a part of many [[radiocontrast|X-ray contrast]] materials in modern medicine. Iodine has only one [[stable isotope]]. A number of iodine radioisotopes are also used in medical applications.

Iodine is found on Earth mainly as the highly water-soluble iodide I<sup>−</sup>, which concentrates it in oceans and brine pools. Like the other [[halogen]]s, free iodine occurs mainly as a [[diatomic]] molecule I<sub>2</sub>, and then only momentarily after being oxidized from iodide by an oxidant like free oxygen.  In the universe and on Earth, iodine's high atomic number makes it a relatively [[Abundance of the chemical elements|rare element]]. However, its presence in ocean water has given it a role in biology (see below).

===Xenon===
{{main|Xenon}}

'''Xenon''' is a [[chemical element]] with the [[chemical symbol|symbol]] '''Xe''' and [[atomic number]] 54. A colorless, heavy, odorless [[noble gas]], xenon occurs in the [[Earth's atmosphere]] in trace amounts.<ref>{{cite encyclopedia
 |author=Staff|year=2007
 |url=http://www.infoplease.com/ce6/sci/A0852881.html
 |title=Xenon|encyclopedia=Columbia Electronic Encyclopedia
 |edition=6th|publisher=Columbia University Press
 |access-date=2007-10-23}}</ref> Although generally unreactive, xenon can undergo a few [[chemical reaction]]s such as the formation of [[xenon hexafluoroplatinate]], the first [[noble gas compound]] to be synthesized.<ref name="lanl">{{cite web
 |author1=Husted, Robert |author2=Boorman, Mollie |date=December 15, 2003
 |url=http://periodic.lanl.gov/54.shtml|title=Xenon
 |publisher=Los Alamos National Laboratory, Chemical Division
 |access-date=2007-09-26
}}</ref><ref>{{cite book
 |last=Rabinovich|first=Viktor Abramovich
 |author2=Vasserman, A. A. |author3=Nedostup, V. I. |author4= Veksler, L. S. |title=Thermophysical properties of neon, argon, krypton, and xenon|year=1988|edition=English-language
 |publisher=Hemisphere Publishing Corp.
 |location=Washington, DC|isbn=0-89116-675-0
 |bibcode=1988wdch...10.....R
 }}—National Standard Reference Data Service of the USSR. Volume 10.</ref><ref name="beautiful">{{cite magazine
 |url=http://www.chem.umn.edu/class/2301/barany03f/fun/beautiful1.pdf
 |title=Chemistry at its Most Beautiful
 |access-date=2007-09-13
 |last=Freemantel
 |first=Michael
 |date=August 25, 2003
 |magazine=Chemical & Engineering News
 |url-status=dead
 |archive-url=https://web.archive.org/web/20160106203608/http://www.chem.umn.edu/class/2301/barany03f/fun/beautiful1.pdf
 |archive-date=January 6, 2016
}}</ref>

Naturally occurring xenon consists of [[Isotopes of xenon|nine stable isotopes]]. There are also over 40 unstable isotopes that undergo [[radioactive decay]]. The isotope ratios of xenon are an important tool for studying the early history of the [[Solar System]].<ref name="kaneoka">{{cite journal
 |last=Kaneoka|first=Ichiro|title=Xenon's Inside Story
 |journal=Science|year=1998|volume=280|issue=5365
 |pages=851–852|doi=10.1126/science.280.5365.851b|s2cid=128502357}}</ref> Radioactive [[xenon-135]] is produced from [[iodine-135]] as a result of [[nuclear fission]], and it acts as the most significant [[neutron absorber]] in [[nuclear reactor]]s.<ref name="stacey">{{cite book
 |first=Weston M.|last=Stacey|year=2007
 |title=Nuclear Reactor Physics|page=213
 |url=https://books.google.com/books?id=y1UgcgVSXSkC&pg=PA213|publisher=Wiley-VCH|isbn=978-3-527-40679-1}}</ref>

Xenon is used in [[xenon flash lamp|flash lamps]]<ref name="burke">{{cite web
 |author=Anonymous|title=History
 |url=http://www.millisecond-cine.com/history.html
 |archive-url=https://web.archive.org/web/20060822141910/http://www.millisecond-cine.com/history.html
 |archive-date=2006-08-22
 |publisher=Millisecond Cinematography
 |access-date=2007-11-07
}}</ref> and [[xenon arc lamp|arc lamps]],<ref name="mellor">{{cite book
 |first=David|last=Mellor|year=2000|page=[https://archive.org/details/soundpersonsguid0000mell/page/186 186]
 |title=Sound Person's Guide to Video
 |publisher=Focal Press
 |isbn=0-240-51595-1|url=https://archive.org/details/soundpersonsguid0000mell|url-access=registration}}</ref> and as a [[general anaesthesia|general anesthetic]].<ref name="Sanders">{{cite journal
 |author1=Sanders, Robert D. |author2=Ma, Daqing |author3=Maze, Mervyn |title=Xenon: elemental anaesthesia in clinical practice
 |journal=British Medical Bulletin
 |year=2005|volume=71|issue=1|pages=115–35
 |doi=10.1093/bmb/ldh034
 |pmid=15728132|doi-access=free}}</ref> The first [[excimer laser]] design used a xenon [[Dimer (chemistry)|dimer]] molecule (Xe<sub>2</sub>) as its [[Active laser medium|lasing medium]],<ref name="basov">{{cite journal
 |doi=10.1070/QE1971v001n01ABEH003011
 |last=Basov|first=N. G.
 |author2=Danilychev, V. A. |author3=Popov, Yu. M.
  |title=Stimulated Emission in the Vacuum Ultraviolet Region
 |journal=Soviet Journal of Quantum Electronics
 |year=1971|volume=1|issue=1|pages=18–22|bibcode = 1971QuEle...1...18B }}</ref> and the earliest [[laser]] designs used xenon flash lamps as [[Laser pumping|pumps]].<ref name="toyserkani">{{cite book
 |last=Toyserkani|first=E.|year=2004
 |author2=Khajepour, A. |author3=Corbin, S. |page=48
 |title=Laser Cladding|publisher=CRC Press
 |isbn=0-8493-2172-7|url=https://books.google.com/books?id=zfvbyCHzVqMC&pg=PA48}}</ref> Xenon is also being used to search for hypothetical [[weakly interacting massive particles]]<ref name="ball">{{cite journal
 |last=Ball|first=Philip|date=May 1, 2002
 |url=http://www.nature.com/news/2002/020429/full/news020429-6.html
 |title=Xenon outs WIMPs|journal=Nature
 |doi=10.1038/news020429-6 |access-date=2007-10-08|url-access=subscription}}</ref> and as the [[propellant]] for [[ion thruster]]s in [[spacecraft]].<ref name="saccoccia">{{cite news
 |last=Saccoccia|first=G. |author2=del Amo, J. G. |author3=Estublier, D.
 |title=Ion engine gets SMART-1 to the Moon
 |date=August 31, 2006|publisher=ESA
 |url=http://www.esa.int/SPECIALS/SMART-1/SEMLZ36LARE_0.html|access-date=2007-10-01}}</ref>

==Biological role==

Rubidium, strontium, yttrium, zirconium, and niobium have no biological role.  Yttrium can cause lung disease in humans.

Molybdenum-containing enzymes are used as catalysts by some bacteria to break the [[chemical bond]] in atmospheric molecular [[nitrogen]], allowing biological [[nitrogen fixation]]. At least 50 molybdenum-containing enzymes are now known in bacteria and animals, though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Owing to the diverse functions of the remainder of the enzymes, molybdenum is a required element for life in higher organisms ([[eukaryotes]]), though not in all bacteria.

Technetium, ruthenium, rhodium, palladium, and silver have no biological role.  Although cadmium has no known biological role in higher organisms, a cadmium-dependent [[carbonic anhydrase]] has been found in marine [[diatom]]s. Rats fed a tin-free diet exhibited improper growth, but the evidence for essentiality is otherwise limited.<ref name=essentialmetals>{{cite journal |last1=Zoroddu |first1=Maria Antonietta |last2=Aaseth |first2=Jan |first3=Guido |last3=Crisponi |first4=Serenella |last4=Medici |first5=Massimiliano |last5=Peana |first6=Valeria Marina |last6=Nurchi |date=2019 |title=The essential metals for humans: a brief overview |url= |journal=Journal of Inorganic Biochemistry |volume=195 |issue= |pages=120–129 |doi=10.1016/j.jinorgbio.2019.03.013 |pmid=30939379 |access-date=}}</ref><ref name="hdl.handle.net">Ultratrace minerals. Authors: Nielsen, Forrest H. USDA, ARS Source: Modern nutrition in health and disease / editors, Maurice E. Shils ... et al.. Baltimore : Williams & Wilkins, c1999., p. 283-303. Issue Date: 1999 URI: [http://hdl.handle.net/10113/46493]</ref> Indium has no biological role and can be toxic as well as antimony.

Tellurium has no biological role, although fungi can incorporate it in place of sulfur and selenium into [[amino acid]]s such as [[tellurocysteine]] and [[telluromethionine]].<ref name="tellurium-fungi">{{Cite journal|doi = 10.1007/BF02917437|title = Incorporation of tellurium into amino acids and proteins in a tellurium-tolerant fungi|year = 1989|last1 = Ramadan|first1 = Shadia E.|last2 = Razak|first2 = A. A.|last3 = Ragab|first3 = A. M.|last4 = El-Meleigy|first4 = M.|journal = Biological Trace Element Research|volume = 20|pages = 225–32|pmid = 2484755|issue = 3| bibcode=1989BTER...20..225R |s2cid = 9439946}}</ref> In humans, tellurium is partly metabolized into [[dimethyl telluride]], (CH<sub>3</sub>)<sub>2</sub>Te, a gas with a [[garlic]]-like odor which is exhaled in the breath of victims of tellurium toxicity or exposure.

Iodine is the heaviest [[essential element]] utilized widely by life in biological functions (only [[tungsten]], employed in enzymes by a few species of bacteria, is heavier). Iodine's rarity in many soils, due to initial low abundance as a crust-element, and also leaching of soluble iodide by rainwater, has led to many deficiency problems in land animals and inland human populations. [[Iodine deficiency]] affects about two billion people and is the leading preventable cause of [[intellectual disabilities]].<ref name="mcneil">{{Cite news|url=https://www.nytimes.com/2006/12/16/health/16iodine.html?fta=y|title=In Raising the World's I.Q., the Secret's in the Salt|last=McNeil|first=Donald G. Jr|date=2006-12-16|work=[[The New York Times]]|access-date=2008-12-04}}</ref>  Iodine is required by higher animals, which use it to synthesize [[thyroid hormones]], which contain the element. Because of this function, [[radioisotopes]] of iodine are concentrated in the [[thyroid gland]] along with nonradioactive iodine. The radioisotope [[iodine-131]], which has a high [[fission product yield]], concentrates in the thyroid, and is one of the most [[carcinogenic]] of [[nuclear fission]] products.

Xenon has no biological role, and is used as a [[General anaesthesia|general anaesthetic]].{{reflist|group=note}}

==References==
{{reflist|colwidth=30em}}

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