Editing Group 4 element (section)

==History==
[[Zircon]] was known as a gemstone from ancient times,<ref name="CRC2008">{{cite book|contribution=Zirconium|date=2007–2008|title=CRC Handbook of Chemistry and Physics|editor-last=Lide|editor-first=David R.|volume=4|page=42|place=New York|publisher=CRC Press|isbn=978-0-8493-0488-0}}</ref> but it was not known to contain a new element until the work of German chemist [[Martin Heinrich Klaproth]] in 1789. He analysed the zircon-containing mineral [[jargoon]] and found a new earth (oxide), but was unable to isolate the element from its oxide. Cornish chemist [[Humphry Davy]] also attempted to isolate this new element in 1808 through [[electrolysis]], but failed: he gave it the name zirconium.<ref name="nbb">{{harvnb|Emsley|2001|pp=506–510}}</ref> In 1824, Swedish chemist [[Jöns Jakob Berzelius]] isolated an impure form of zirconium, obtained by heating a mixture of potassium and potassium zirconium fluoride in an iron tube.<ref name="CRC2008"/>

Cornish mineralogist [[William Gregor]] first identified titanium in ilmenite sand beside a stream in [[Cornwall]], Great Britain in the year 1791.<ref name="Emsley2001p452">{{harvnb|Emsley|2001|p=452}}</ref> After analyzing the sand, he determined the weakly magnetic sand to contain [[iron oxide]] and a metal oxide that he could not identify.<ref name="Barksdale1968p732">{{harvnb|Barksdale|1968|p=732}}</ref> During that same year, mineralogist [[Franz Joseph Muller]] produced the same metal oxide and could not identify it. In 1795, chemist [[Martin Heinrich Klaproth]] independently rediscovered the metal oxide in [[rutile]] from the Hungarian village Boinik.<ref name="Emsley2001p452" /> He identified the oxide containing a new element and named it for the [[titan (mythology)|Titans]] of [[Greek mythology]].<ref name="weeksIII">{{cite journal|last = Weeks|first = Mary Elvira|author-link=Mary Elvira Weeks|year = 1932|title = III. Some Eighteenth-Century Metals|journal = Journal of Chemical Education|pages = 1231–1243|doi = 10.1021/ed009p1231|volume = 9|issue = 7|bibcode = 1932JChEd...9.1231W }}</ref> Berzelius was also the first to prepare titanium metal (albeit impurely), doing so in 1825.<ref name=Greenwood954>Greenwood and Earnshaw, p. 954</ref>

The [[X-ray spectroscopy]] done by [[Henry Moseley]] in 1914 showed a direct dependency between [[spectral line]] and [[effective nuclear charge]]. This led to the nuclear charge, or [[atomic number]] of an element, being used to ascertain its place within the periodic table. With this method, Moseley determined the number of [[lanthanides]] and showed that there was a missing element with atomic number 72.<ref>{{cite journal|last = Heilbron|title=The Work of H. G. J. Moseley|first = John L.|volume=57|page=336|date=1966|journal=Isis|doi=10.1086/350143|issue = 3|s2cid=144765815}}</ref> This spurred chemists to look for it.<ref>{{cite journal|last = Heimann|first = P. M.|date = 1967|title = Moseley and celtium: The search for a missing element|journal = [[Annals of Science]]|volume = 23|pages=249–260|doi = 10.1080/00033796700203306|issue = 4}}</ref> [[Georges Urbain]] asserted that he found element 72 in the [[rare earth element]]s in 1907 and published his results on ''celtium'' in 1911.<ref>{{cite journal|last = Urbain|first = M. G.|title = Sur un nouvel élément qui accompagne le lutécium et le scandium dans les terres de la gadolinite: le celtium (On a new element that accompanies lutetium and scandium in gadolinite: celtium)|journal = Comptes Rendus|page=141|url = http://gallica.bnf.fr/ark:/12148/bpt6k3105c/f141.table|access-date=2008-09-10|date = 1911|language = fr}}</ref> Neither the spectra nor the chemical behavior he claimed matched with the element found later, and therefore his claim was turned down after a long-standing controversy.<ref name="Mel">{{cite journal|journal = Centaurus|volume = 26|pages =317–322|title = Some Details in the Prehistory of the Discovery of Element 72|first = V. P.|last = Mel'nikov|doi = 10.1111/j.1600-0498.1982.tb00667.x|date = 1982|bibcode = 1982Cent...26..317M|issue = 3 }}</ref>

By early 1923, several physicists and chemists such as [[Niels Bohr]]<ref>{{cite book|title = The Theory of Spectra and Atomic Constitution: Three Essays|url = https://archive.org/details/TheTheoryOfSpectraAndAtomicConstitution|first = Niels|last = Bohr| date=June 2008 |page=[https://archive.org/details/TheTheoryOfSpectraAndAtomicConstitution/page/n123 114]| publisher=Kessinger |isbn = 978-1-4365-0368-6}}</ref> and [[Charles Rugeley Bury]]<ref>{{cite journal|journal = J. Am. Chem. Soc.|title = Langmuir's Theory of the Arrangement of Electrons in Atoms and Molecules|first = Charles R.|last = Bury|volume = 43|date = 1921|pages=1602–1609|doi = 10.1021/ja01440a023|issue = 7|url = https://zenodo.org/record/1428812}}</ref> suggested that element 72 should resemble zirconium and therefore was not part of the rare earth elements group. These suggestions were based on Bohr's theories of the atom, the X-ray spectroscopy of Moseley, and the chemical arguments of [[Friedrich Paneth]].<ref>{{cite book|first = F. A.|last = Paneth|chapter = Das periodische System (The periodic system)|title = Ergebnisse der Exakten Naturwissenschaften 1|date =1922|page=362|language = de}}</ref><ref>{{cite journal|title = Hafnium|url = http://www.jce.divched.org/Journal/Issues/1982/Mar/jceSubscriber/JCE1982p0242.pdf|journal = Journal of Chemical Education|last = Fernelius|first = W. C.|date = 1982|page = 242|doi = 10.1021/ed059p242|volume = 59|issue = 3|bibcode = 1982JChEd..59..242F|access-date = 2021-02-03|archive-date = 2020-03-15|archive-url = https://web.archive.org/web/20200315031648/http://www.jce.divched.org/Journal/Issues/1982/Mar/jceSubscriber/JCE1982p0242.pdf|url-status = dead}}</ref> Encouraged by this, and by the reappearance in 1922 of Urbain's claims that element 72 was a rare earth element discovered in 1911, [[Dirk Coster]] and [[Georg von Hevesy]] were motivated to search for the new element in zirconium ores.<ref>{{cite journal|volume = 174|date = 1922|last = Urbain|first = M. G.|title = Sur les séries L du lutécium et de l'ytterbium et sur l'identification d'un celtium avec l'élément de nombre atomique 72 |trans-title=The L series from lutetium to ytterbium and the identification of element 72 celtium|journal = Comptes Rendus|page=1347|url = http://gallica.bnf.fr/ark:/12148/bpt6k3127j/f1348.table|access-date=2008-10-30|language = fr}}</ref> [[Hafnium]] was discovered by the two in 1923 in Copenhagen, Denmark.<ref>{{cite journal|journal = Nature|volume = 111|page=79|date=1923|doi = 10.1038/111079a0|title = On the Missing Element of Atomic Number 72|first = D.|last = Coster|author2=Hevesy, G.|issue=2777|bibcode=1923Natur.111...79C|doi-access = free}}</ref><!--follow up publications of Urbain's claim that celtium and hafnium are identical {{doi|10.1038/111218a0}}{{doi|10.1038/111252a0}}--><ref>{{cite journal|title = The Discovery and Properties of Hafnium|first = G.|last = Hevesy|journal = Chemical Reviews|date = 1925|volume = 2|pages=1–41|doi = 10.1021/cr60005a001}}</ref> The place where the discovery took place led to the element being named for the Latin name for "Copenhagen", ''Hafnia'', the home town of [[Niels Bohr]].<ref name ="Scerri">{{cite journal|title = Prediction of the nature of hafnium from chemistry, Bohr's theory and quantum theory|first = Eric R.|last = Scerri|journal = Annals of Science|date = 1994|volume = 51|pages= 137–150|doi =10.1080/00033799400200161|issue = 2}}</ref>

Hafnium was separated from zirconium through repeated recrystallization of the double [[ammonium]] or [[potassium]] fluorides by [[Valdemar Thal Jantzen]] and von Hevesy.<ref name="Ark1924a" >{{cite journal|title = Die Trennung von Zirkonium und Hafnium durch Kristallisation ihrer Ammoniumdoppelfluoride (The separation of zirconium and hafnium by crystallization of the double ammonium fluorides)|journal = Zeitschrift für Anorganische und Allgemeine Chemie|volume = 141|date = 1924|pages= 284–288|first = A. E.|last = van Arkel|author2 = de Boer, J. H.|doi = 10.1002/zaac.19241410117|language = de}}</ref> [[Anton Eduard van Arkel]] and [[Jan Hendrik de Boer]] were the first to prepare metallic hafnium by passing hafnium tetraiodide vapor over a heated [[tungsten]] filament in 1924.<ref name="Ark1924b">{{cite journal|title = Die Trennung des Zirkoniums von anderen Metallen, einschließlich Hafnium, durch fraktionierte Distillation (The separation of zirconium and hafnium by fractionated distillation)| journal = Zeitschrift für Anorganische und Allgemeine Chemie|volume = 141|date = 1924|pages= 289–296|first = A. E.|last = van Arkel|author2 = de Boer, J. H.|doi = 10.1002/zaac.19241410118|language = de}}</ref><ref name="Ark1925">{{cite journal|title = Darstellung von reinem Titanium-, Zirkonium-, Hafnium- und Thoriummetall (Production of pure titanium, zirconium, hafnium and Thorium metal)|journal = Zeitschrift für Anorganische und Allgemeine Chemie|volume = 148|date = 1925|pages= 345–350|first = A. E.|last = van Arkel|author2 = de Boer, J. H.|doi = 10.1002/zaac.19251480133|language = de}}</ref> The long delay between the discovery of the lightest two group 4 elements and that of hafnium was partly due to the rarity of hafnium, and partly due to the extreme similarity of zirconium and hafnium, so that all previous samples of zirconium had in reality been contaminated with hafnium without anyone knowing.<ref name="EncyChem">{{cite book|editor-last=Hampel|editor-first=Clifford A.|title=The Encyclopedia of the Chemical Elements|year=1968|last=Barksdale|first=Jelks|publisher=Reinhold Book Corporation|location=Skokie, Illinois|pages=732–738|chapter=Titanium|lccn=68-29938}}</ref>

The last element of the group, [[rutherfordium]], does not occur naturally and had to be made by synthesis. The first reported detection was by a team at the [[Joint Institute for Nuclear Research]] (JINR), which in 1964 claimed to have produced the new element by bombarding a [[plutonium]]-242 target with [[neon]]-22 ions, although this was later put into question.<ref name=93TWG>{{cite journal |title =Discovery of the transfermium elements. Part II: Introduction to discovery profiles. Part III: Discovery profiles of the transfermium elements |date = 1993 |author= Barber, R. C. |author2=Greenwood, N. N. |author3=Hrynkiewicz, A. Z. |author4=Jeannin, Y. P. |author5=Lefort, M. |author6=Sakai, M. |author7=Ulehla, I. |author8=Wapstra, A. P. |author9= Wilkinson, D. H. |journal = Pure and Applied Chemistry| volume = 65 |issue = 8 |pages = 1757–1814 |doi = 10.1351/pac199365081757|s2cid = 195819585 |doi-access= free }}</ref> More conclusive evidence was obtained by researchers at the [[University of California, Berkeley]], who synthesised element 104 in 1969 by bombarding a [[californium]]-249 target with [[carbon-12]] ions.<ref name=69Gh01>{{cite journal |doi = 10.1103/PhysRevLett.22.1317 |title = Positive Identification of Two Alpha-Particle-Emitting Isotopes of Element 104 |date = 1969 |last1 = Ghiorso |first1 = A. |last2 = Nurmia |first2=M. |journal = Physical Review Letters |volume = 22 |issue = 24 |pages = 1317–1320 |bibcode=1969PhRvL..22.1317G|last3 = Harris |first3 = J. |last4 = Eskola |first4 = K. |last5 = Eskola |first5 = P. |url = https://cloudfront.escholarship.org/dist/prd/content/qt3fm666nq/qt3fm666nq.pdf }}</ref> A [[Transfermium Wars|controversy]] erupted on who had discovered the element, which each group suggesting its own name: the Dubna group named the element ''kurchatovium'' after [[Igor Kurchatov]], while the Berkeley group named it ''rutherfordium'' after [[Ernest Rutherford]].<ref>{{cite web |url=http://www.rsc.org/chemistryworld/podcast/Interactive_Periodic_Table_Transcripts/Rutherfordium.asp |title=Rutherfordium |publisher=Rsc.org |access-date=2010-09-04}}</ref> Eventually a joint working party of [[IUPAC]] and [[IUPAP]], the Transfermium Working Group, decided that credit for the discovery should be shared. After various compromises were attempted, in 1997, IUPAC officially named the element rutherfordium following the American proposal.<ref name=97IUPAC>{{cite journal |doi =10.1351/pac199769122471 |title =Names and symbols of transfermium elements (IUPAC Recommendations 1997) |date =1997 |journal =Pure and Applied Chemistry |volume =69 |issue = 12 |pages =2471–2474|doi-access =free }}</ref>