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ఆవర్తన పట్టిక: కూర్పుల మధ్య తేడాలు

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ట్యాగు: 2017 source edit
పంక్తి 152:
[[File:Mendeleev's 1869 periodic table.png|upright=1.15|thumb|right|Mendeleev's 1869 periodic table; note that his arrangement presents the periods vertically, and the groups horizontally.]]
 
రష్యన్ రసాయన శాస్త్రవేత్త [[డిమిట్రీ మెండలీఫ్|డిమిట్రీ మెండలియెవ్]] 1869లో , జర్మన్ రసాయన శాస్త్రవేత్త జూలియస్ లోథర్‌మేయర్ 1870లో వేర్వేరుగా ఆవర్తన పట్టికలను రూపొందించారు<ref>{{cite journal|last=Mendelejew |first=Dimitri |year=1869 |title=Über die Beziehungen der Eigenschaften zu den Atomgewichten der Elemente |journal=Zeitschrift für Chemie |pages=405–406 |language=German}}</ref>. ఇద్దరూ తమ తమ ఆవర్తన పట్టికలలో మూలకాలను నిలువు వరుసలు, అడ్డు వరుసలలో వాటి పరమాణు భారాల ఆరోహణ క్రమంలో అమర్చి తయారు చేసారు. ఆవర్తన ధర్మల ఆధారంగా నిలువు వరుసలలో మూలకాలను అమర్చారు<ref>Ball, pp. 100–102</ref>. మెండలీవ్ పట్టికకు లభించిన గుర్తింపు, అంగీకారం అతను తీసుకున్న రెండు నిర్ణయాల నుండి వచ్చింది. మొదటిది అతను సరైన ధర్మాలు గల అప్పటికి కనుగొనని మూలకాలు స్థానాలలో ఖాళీలనుంచాడు<ref>{{cite book |author=Pullman, Bernard |title=The Atom in the History of Human Thought |publisher=Oxford University Press |year=1998 |page=227 |isbn=0-19-515040-6|others=Translated by Axel Reisinger}}</ref>. మెండెలీవ్ ఊహించినట్లుగా సరిగ్గా ఎకా సిలికాన్, (జెర్మేనియం), ఎకా అల్యూమినియం, (గాలియం) మరియు ఎకాబోరాన్ (స్కాండియం) మూలకాలు కనుగొనడం వలన మెండలీవ్‌కు అత్యధికంగా గుర్తింపు వచ్చింది. కొందరయితే మెండలీవ్ చెప్పినట్లుగా ఇంకా చాలా క్రొత్త మూలకాలు కనుగోవడం భ్రమ అని కొట్టిపారేశారు కాని Ga (గాలియం), Ge ([[జెర్మేనియం]]) మూలకాలను 1875లోను, 1886లోను సరిగ్గా మెండలీవ్ చెప్పిన ఖాళీలలో కనుగొన్నారు<ref>Ball, p. 105</ref>. రెండవ నిర్ణయం అప్పుడప్పుడు ప్రక్క ప్రక్క మూలకాల పరమాణు భారాల ఆరోహణ క్రమాన్ని విస్మరించి ఆ మూలకాల క్రమాన్ని మార్చడం. ఒక మూలకం యొక్క లక్షణాలను బట్టి, దానికి ముందు వెనుకల ఉన్న మూలకాల పరమాణు భారాలను బట్టి, దాని పరమాణుభారం అంచనాను మార్చుకొనవచ్చును. ఉదాహరణకు టెల్లీరియం పరమాణు భారం 123 మరియు 126 మధ్య ఉండాలి. 128 కారాదు. (ఇక్కడ మెండలియెవ్ అంచనా తప్పింది. టెల్లూరియం పరమాణుభారం 127.6, ఇది అయొడీన్ పరమాణు భారమైన 126.9 కంటే ఎక్కువ.) {{Authority control}}
Mendeleev published in 1869, using atomic weight to organize the elements, information determinable to fair precision in his time. Atomic weight worked well enough to allow Mendeleev to accurately predict the properties of missing elements.
 
Mendeleev took the unusual step of naming missing elements using the [[Sanskrit]] numerals ''eka'' (1), ''dvi'' (2), and ''tri'' (3) to indicate that the element in question was one, two, or three rows removed from a lighter congener. It has been suggested that Mendeleev, in doing so, was paying homage to ancient [[Sanskrit grammar]]ians, in particular [[Pāṇini]], who devised a periodic alphabet for the language.<ref>{{Cite journal|last=Ghosh|first=Abhik|last2=Kiparsky|first2=Paul|date=2019|title=The Grammar of the Elements|journal=American Scientist|volume=107|issue=6|pages=350|doi=10.1511/2019.107.6.350|issn=0003-0996}}</ref>
 
[[File:Henry Moseley (1887-1915).jpg|thumb|Henry Moseley (1887–1915)]]
Following the discovery of the atomic nucleus by [[Ernest Rutherford]] in 1911, it was proposed that the integer count of the nuclear charge is identical to the sequential place of each element in the periodic table. In 1913, English physicist [[Henry Moseley]] using [[X-ray spectroscopy]] confirmed this proposal experimentally. Moseley determined the value of the nuclear charge of each element and showed that Mendeleev's ordering actually places the elements in sequential order by nuclear charge.<ref>{{cite book |title=The Periodic Kingdom |author=Atkins, P. W. |authorlink=P. W. Atkins |publisher=HarperCollins Publishers, Inc. |year=1995 |page=[https://archive.org/details/periodickingdomj00atki/page/87 87] |isbn=978-0-465-07265-1 |url=https://archive.org/details/periodickingdomj00atki/page/87 }}</ref> Nuclear charge is identical to [[proton]] count and determines the value of the [[atomic number]] (''Z'') of each element. Using atomic number gives a definitive, integer-based sequence for the elements. Moseley predicted, in 1913, that the only elements still missing between aluminium (''Z''&nbsp;=&nbsp;13) and gold (''Z''&nbsp;=&nbsp;79) were ''Z''&nbsp;= 43, 61, 72, and 75, all of which were later discovered. The atomic number is the absolute definition of an [[Chemical element|element]] and gives a factual basis for the ordering of the periodic table.<ref name=":0">{{cite journal |journal=Nucl. Phys. A |volume=789 |issue=1–4 |pages=142–154 |year=2007 |title=Predictions of alpha decay half-lifes of heavy and superheavy elements |last1=Samanta |first1=C. |last2=Chowdhury |first2=P. Roy |last3=Basu |first3=D. N. |doi=10.1016/j.nuclphysa.2007.04.001 |bibcode=2007NuPhA.789..142S |arxiv = nucl-th/0703086 |citeseerx=10.1.1.264.8177}}</ref>
 
===Second version and further development===
[[File:Periodic table by Mendeleev, 1871.svg|thumb|left|upright=2.27|Mendeleev's 1871 periodic table with eight groups of elements. Dashes represented elements unknown in 1871.]] [[File:ShortPT20b.png|thumb|left|upright=2.27|Eight-group form of periodic table, updated with all elements discovered to 2016]]
In 1871, Mendeleev published his periodic table in a new form, with groups of similar elements arranged in columns rather than in rows, and those columns numbered I to VIII corresponding with the element's oxidation state. He also gave detailed predictions for the properties of elements he had earlier noted were missing, but should exist.<ref>Scerri 2007, p. 112</ref> These gaps were subsequently filled as chemists discovered additional naturally occurring elements.<ref>{{cite journal |last=Kaji |first=M. |year=2002 |title=D. I. Mendeleev's Concept of Chemical Elements and the Principle of Chemistry |journal=[[Bull. Hist. Chem.]] |volume=27 |issue=1 |pages=4–16 |url=http://www.scs.illinois.edu/~mainzv/HIST/awards/OPA%20Papers/2005-Kaji.pdf |url-status=live |archiveurl=https://archive.is/20160706091143/http://www.scs.illinois.edu/~mainzv/HIST/awards/OPA%20Papers/2005-Kaji.pdf |archivedate=6 July 2016 |df=dmy-all }}</ref> It is often stated that the last naturally occurring element to be discovered was [[francium]] (referred to by Mendeleev as ''eka-caesium'') in 1939.<ref>{{cite web|url=http://chemeducator.org/sbibs/s0010005/spapers/1050387gk.htm |title=Francium (Atomic Number 87), the Last Discovered Natural Element |last1=Adloff |first1=J-P. |last2=Kaufman |first2=G. B. |date=25 September 2005 |publisher=The Chemical Educator |accessdate=26 March 2007 |url-status=dead |archiveurl=https://web.archive.org/web/20130604212956/http://chemeducator.org/sbibs/s0010005/spapers/1050387gk.htm |archivedate=4 June 2013 |df= }}</ref> [[Plutonium]], produced synthetically in 1940, was identified in trace quantities as a naturally occurring element in 1971.<ref>{{cite journal |doi = 10.1038/234132a0 |title = Detection of Plutonium-244 in Nature |journal = Nature |pages = 132–134 |year = 1971 |last1 = Hoffman |first1 = D. C. |last2 = Lawrence |first2 = F. O. |last3 = Mewherter |first3 = J. L. |last4 = Rourke |first4 = F. M. |volume = 234 |bibcode = 1971Natur.234..132H |issue = 5325 |df = dmy-all |url = https://www.semanticscholar.org/paper/1c4b392ced6dcb26ab71bbfe84b0a1e9efb7bc96 }}</ref>
 
The popular<ref>Gray, p.&nbsp; 12</ref> periodic table layout, also known as the common or standard form (as shown at various other points in this article), is attributable to Horace Groves Deming. In 1923, Deming, an American chemist, published short ([http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=456 Mendeleev style]) and medium ([http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=360 18-column]) form periodic tables.<ref>{{cite book |last=Deming|first=H. G.|title=General chemistry: An elementary survey|year=1923 |publisher=J. Wiley & Sons |location=New York |pages =160, 165}}</ref>{{#tag:ref|An antecedent of Deming's 18-column table may be seen in [http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=67 Adams' 16-column Periodic Table of 1911]. Adams omits the rare earths and the "radioactive elements" (i.e. the actinides) from the main body of his table and instead shows them as being "[[wikt:caret|careted]] in only to save space" (rare earths between Ba and eka-Yt; radioactive elements between eka-Te and eka-I). See: Elliot Q. A. (1911). "A modification of the periodic table". ''Journal of the American Chemical Society''. '''33'''(5): 684–688 (687).|group=n}} Merck and Company prepared a handout form of Deming's 18-column medium table, in 1928, which was widely circulated in American schools. By the 1930s Deming's table was appearing in handbooks and encyclopedias of chemistry. It was also distributed for many years by the Sargent-Welch Scientific Company.<ref>{{cite book|last1=Abraham |first1=M. |last2=Coshow |first2=D. |last3=Fix |first3=W. |title=Periodicity:A source book module, version 1.0 |publisher=Chemsource, Inc. |location=New York |page=3 |url=http://dwb4.unl.edu/chem_source_pdf/PERD.pdf |url-status=dead |archiveurl=https://web.archive.org/web/20120514182242/http://dwb4.unl.edu/chem_source_pdf/PERD.pdf |archivedate=14 May 2012 |df= }}</ref><ref>{{cite journal|last=Emsley|first=J.|title=Mendeleyev's dream table|journal=New Scientist|date=7 March 1985|pages=32–36(36)}}</ref><ref>{{cite journal|last=Fluck|first=E.|year=1988|title=New notations in the period table|journal=Pure and Applied Chemistry|volume=60|issue= 3|pages=431–436 (432)|doi=10.1351/pac198860030431}}</ref>
 
With the development of modern [[quantum mechanics|quantum mechanical]] theories of [[electron]] configurations within atoms, it became apparent that each period (row) in the table corresponded to the filling of a [[electron shell|quantum shell]] of electrons. Larger atoms have more electron sub-shells, so later tables have required progressively longer periods.<ref>Ball, p. 111</ref>
 
[[File:Glenn Seaborg - 1964.jpg|thumb|right|upright=0.7|[[Glenn T. Seaborg]], in 1945, suggested a new periodic table showing the actinides as belonging to a second f-block series.]]
 
In 1945, [[Glenn T. Seaborg|Glenn Seaborg]], an American scientist, made the [[actinide concept|suggestion]] that the [[actinides|actinide elements]], like the [[lanthanides]], were filling an f sub-level. Before this time the actinides were thought to be forming a fourth d-block row. Seaborg's colleagues advised him not to publish such a radical suggestion as it would most likely ruin his career. As Seaborg considered he did not then have a career to bring into disrepute, he published anyway. Seaborg's suggestion was found to be correct and he subsequently went on to win the 1951 [[Nobel Prize]] in chemistry for his work in synthesizing actinide elements.<ref>Scerri 2007, pp. 270‒71</ref><ref>{{cite book |last1=Masterton|first1=W. L. |last2=Hurley|first2=C. N.|last3=Neth|first3=E. J.|title=Chemistry: Principles and reactions|publisher=Brooks/Cole Cengage Learning|location=Belmont, CA|edition=7th|isbn=978-1-111-42710-8|page=173|date=2011-01-31 }}</ref>{{#tag:ref|A second extra-long periodic table row, to accommodate known and undiscovered elements with an atomic weight greater than bismuth (thorium, protactinium and uranium, for example), had been postulated as far back as 1892. Most investigators considered that these elements were analogues of the third series transition elements, hafnium, tantalum and tungsten. The existence of a second inner transition series, in the form of the actinides, was not accepted until similarities with the electron structures of the lanthanides had been established. See: van Spronsen, J. W. (1969). ''The periodic system of chemical elements''. Amsterdam: Elsevier. p. 315–316, {{ISBN|0-444-40776-6}}.|group=n}}
 
Although minute quantities of some [[transuranic elements]] occur naturally,<ref name="emsley"/> they were all first discovered in laboratories. Their production has expanded the periodic table significantly, the first of these being [[neptunium]], synthesized in 1939.<ref>Ball, p. 123</ref> Because many of the transuranic elements are highly unstable and [[radioactivity|decay]] quickly, they are challenging to detect and characterize when produced. There have been [[element naming controversy|controversies]] concerning the acceptance of competing discovery claims for some elements, requiring independent review to determine which party has priority, and hence naming rights.<ref>{{cite journal |last1=Barber|first1= R. C.|last2=Karol|first2=P. J.|last3=Nakahara|first3=Hiromichi|last4= Vardaci|first4= Emanuele|last5=Vogt|first5= E. W. |title=Discovery of the elements with atomic numbers greater than or equal to 113 (IUPAC Technical Report) |doi=10.1351/PAC-REP-10-05-01 |journal=Pure Appl. Chem. |year=2011 |volume=83 |issue=7|page=1485}}</ref> In 2010, a joint Russia–US collaboration at [[Dubna]], [[Moscow Oblast]], Russia, claimed to have synthesized six atoms of [[tennessine]] (element 117), making it the most recently claimed discovery. It, along with [[nihonium]] (element 113), [[moscovium]] (element 115), and [[oganesson]] (element 118), are the four most recently named elements, whose names all became official on 28 November 2016.<ref name=E117>{{cite web|script-title=ru:Эксперимент по синтезу 117-го элемента получает продолжение|trans-title=Experiment on synthesis of the 117th element is to be continued|url=http://www.jinr.ru/news_article.asp?n_id=1195&language=rus|year=2012|publisher=JINR|language=ru|url-status=live|archiveurl=https://web.archive.org/web/20130801120735/http://www.jinr.ru/news_article.asp?n_id=1195&language=rus|archivedate=1 August 2013|df=dmy-all}}</ref>
 
==Different periodic tables==
 
===The long- or 32-column table===
[[File:32-column periodic table-a.png|upright=2.95|thumb|The periodic table in 32-column format]]
The modern periodic table is sometimes expanded into its long or 32-column form by reinstating the footnoted f-block elements into their natural position between the s- and d-blocks, as proposed by [[Alfred Werner]].<ref>{{Cite journal|last=Werner|first=Alfred|date=1905|title=Beitrag zum Ausbau des periodischen Systems|journal=Berichte der Deutschen Chemischen Gesellschaft|volume=38|pages=914–921|doi=10.1002/cber.190503801163}}</ref> Unlike the 18-column form this arrangement results in "no interruptions in the sequence of increasing atomic numbers".<ref>{{cite book | chapter-url = https://books.google.com/books?id=spjcrJ0UjbsC&pg=PA190 | last = Scerri | first = Eric | authorlink = Eric Scerri | title = A Tale of 7 Elements | chapter = Element 61{{snd}}Promethium | place = New York | publisher = [[Oxford University Press]] (US) | isbn = 978-0-19-539131-2 | pages = [https://archive.org/details/taleofseveneleme0000scer/page/175 175–194 (190)] | year = 2013 | quote = ...&nbsp;no interruptions in the sequence of increasing atomic numbers&nbsp;... | url-status = live | df = dmy-all | url = https://archive.org/details/taleofseveneleme0000scer/page/175 }}</ref> The relationship of the f-block to the other blocks of the periodic table also becomes easier to see.<ref>{{cite book |url=https://books.google.com/books?id=rysqAAAACAAJ |last=Newell |first=S. B. |title=Chemistry: An introduction |place=Boston |publisher=Little, Brown and Company |page=196 |isbn=978-0-316-60455-0 |year=1980 |accessdate=27 August 2016 |archive-url=https://web.archive.org/web/20190328013723/https://books.google.com/books?id=rysqAAAACAAJ |archive-date=28 March 2019 |url-status=live }}</ref> [[William B. Jensen|Jensen]] advocates a form of table with 32 columns on the grounds that the lanthanides and actinides are otherwise relegated in the minds of students as dull, unimportant elements that can be quarantined and ignored.<ref name="Jensen"/> Despite these advantages the 32-column form is generally avoided by editors on account of its undue rectangular ratio compared to a book page ratio,<ref>{{cite journal|last=Leach|first = M. R.|title=Concerning electronegativity as a basic elemental property and why the periodic table is usually represented in its medium form|journal= Foundations of Chemistry|volume=15|issue=1|pages=13–29|doi=10.1007/s10698-012-9151-3|year=2012|url = https://www.semanticscholar.org/paper/720904ce47694ca4f8523ae5c10f9da3a2836ddf}}</ref> and the familiarity of chemists with the modern form, as introduced by Seaborg.<ref>{{cite book|last=Thyssen|first=P.|last2=Binnemans|first2=K.|editor1-last=Gschneidner Jr.|editor1-first= K. A.|editor2-last=Bünzli|editor2-first=J-C.G|editor3-last=Vecharsky|editor3-first=Bünzli|date=2011|title=Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis|journal=Handbook on the Physics and Chemistry of Rare Earths|publisher=Elsevier|location=Amsterdam|volume=41|page=76|isbn=978-0-444-53590-0}}</ref>
 
{{Periodic table (32 columns, detailed cells)}}
 
===Tables with different structures===
{{main|Alternative periodic tables}}
Within 100 years of the appearance of Mendeleev's table in 1869, [[Edward G. Mazurs]] had collected an estimated 700 different published versions of the periodic table.<ref name="Jensen">{{cite journal|last1=Jensen|first1=William B.|title=Classification, symmetry and the periodic table|journal=Comp. & Maths. With Appls.|date=1986|volume=12B|issue=I/2|url=http://www.che.uc.edu/Jensen/W.%20B.%20Jensen/Reprints/028.%20Periodic%20Table.pdf|accessdate=18 January 2017|archive-url=https://web.archive.org/web/20170131184706/http://www.che.uc.edu/Jensen/W.%20B.%20Jensen/Reprints/028.%20Periodic%20Table.pdf|archive-date=31 January 2017|url-status=live}}</ref><ref name="Papers">{{Cite book|title=Finding Aid to Edward G. Mazurs Collection of Periodic Systems Images|url=http://othmerlib.sciencehistory.org/record=b1069103~S6|website=[[Science History Institute]]|quote="Click on 'Finding Aid' to go to full finding aid."|access-date=2 October 2018|archive-url=https://web.archive.org/web/20190327082328/http://othmerlib.sciencehistory.org/record%3Db1069103~S6|archive-date=27 March 2019|url-status=live}}</ref><ref name=Scerri20>Scerri 2007, p. 20</ref> As well as numerous rectangular variations, other periodic table formats have been shaped, for example,{{#tag:ref|See [http://www.meta-synthesis.com/webbook//35_pt/pt_database.php ''The Internet database of periodic tables''] for depictions of these kinds of variants.|group=n}} like a circle, cube, cylinder, building, spiral, [[lemniscate]],<ref>{{cite web |url=http://cultureofchemistry.fieldofscience.com/2009/03/weird-words-of-science-lemniscate.html |title=Weird Words of Science: Lemniscate Elemental Landscapes |last= |first= |publisher=fieldofscience.com |date=22 March 2009 |website=Fields of Science |access-date=4 January 2016 |url-status=live |archiveurl=https://web.archive.org/web/20160304033830/http://cultureofchemistry.fieldofscience.com/2009/03/weird-words-of-science-lemniscate.html |archivedate=4 March 2016 |df=dmy-all }}</ref> octagonal prism, pyramid, sphere, or triangle. Such alternatives are often developed to highlight or emphasize chemical or physical properties of the elements that are not as apparent in traditional periodic tables.<ref name=Scerri20/>
 
[[File:Elementspiral (polyatomic).svg|thumb|left|Theodor Benfey's spiral periodic table]]
A popular<ref>{{cite journal |last1=Emsely |first1=J. |last2=Sharp |first2=R. |title=The periodic table: Top of the charts |journal=The Independent |date=21 June 2010 |url=https://www.independent.co.uk/news/science/the-periodic-table-top-of-the-charts-2005992.html |url-status=live |archiveurl=https://web.archive.org/web/20170701044605/http://www.independent.co.uk/news/science/the-periodic-table-top-of-the-charts-2005992.html |archivedate=1 July 2017 |df=dmy-all }}</ref> alternative structure is that of [[Otto Theodor Benfey]] (1960). The elements are arranged in a continuous spiral, with hydrogen at the centre and the transition metals, lanthanides, and actinides occupying peninsulas.<ref>{{cite journal |last=Seaborg |first=G. |year=1964 |title=Plutonium: The Ornery Element |journal=Chemistry |volume=37 |issue=6 |page=14}}</ref>
 
Most periodic tables are two-dimensional;<ref name=emsley/> three-dimensional tables are known to as far back as at least 1862 (pre-dating Mendeleev's two-dimensional table of 1869). More recent examples include Courtines' Periodic Classification (1925),<ref>{{cite web |url=http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=65 |title=1925 Courtines' Periodic Classification |author=Mark R. Leach |accessdate=16 October 2012 |url-status=live |archiveurl=http://arquivo.pt/wayback/20160516164123/http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=65 |archivedate=16 May 2016 |df=dmy-all }}</ref> Wringley's Lamina System (1949),<ref>{{cite web |url=http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=295 |title=1949 Wringley's Lamina System |author=Mark R. Leach |accessdate=16 October 2012 |url-status=live |archiveurl=https://web.archive.org/web/20111203150155/http://meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=295 |archivedate=3 December 2011 |df=dmy-all }}</ref>
[[Paul-Antoine Giguère|Giguère]]'s Periodic helix (1965)<ref>{{cite book |title=Graphical Representations of the Periodic System During One Hundred Years |last=Mazurs |first= E. G. |year= 1974 |publisher=University of Alabama Press |location=Alabama |page=111 |isbn=978-0-8173-3200-6}}</ref> and Dufour's Periodic Tree (1996).<ref>{{cite web |url=http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=39 |title=1996 Dufour's Periodic Tree |author=Mark R. Leach |accessdate=16 October 2012 |url-status=live |archiveurl=https://web.archive.org/web/20100418074643/http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=39 |archivedate=18 April 2010 |df=dmy-all }}</ref> Going one further, Stowe's Physicist's Periodic Table (1989)<ref>{{cite web |url=http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=38 |title=1989 Physicist's Periodic Table by Timothy Stowe |author=Mark R. Leach |accessdate=16 October 2012 |url-status=live |archiveurl=https://web.archive.org/web/20120605031716/http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=38 |archivedate=5 June 2012 |df=dmy-all }}</ref> has been described as being four-dimensional (having three spatial dimensions and one colour dimension).<ref>{{cite journal|last=Bradley|first=D.|title=At last, a definitive periodic table?|journal=ChemViews Magazine|date=20 July 2011|url=http://www.chemistryviews.org/details/ezine/1247399/At_Last_A_Definitive_Periodic_Table.html|doi=10.1002/chemv.201000107|url-status=live|archiveurl=https://web.archive.org/web/20130501091625/http://www.chemistryviews.org/details/ezine/1247399/At_Last_A_Definitive_Periodic_Table.html|archivedate=1 May 2013|df=dmy-all}}</ref>
 
The various forms of periodic tables can be thought of as lying on a chemistry–physics continuum.<ref>Scerri 2007, pp. 285‒86</ref> Towards the chemistry end of the continuum can be found, as an example, Rayner-Canham's "unruly"<ref>Scerri 2007, p. 285</ref> Inorganic Chemist's Periodic Table (2002),<ref>{{cite web|url=http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=429|title=2002 Inorganic Chemist's Periodic Table|author=Mark R. Leach|accessdate=16 October 2012|url-status=live|archiveurl=https://web.archive.org/web/20130309084637/http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=429|archivedate=9 March 2013|df=dmy-all}}</ref> which emphasizes trends and patterns, and unusual chemical relationships and properties. Near the physics end of the continuum is [[Charles Janet|Janet]]'s Left-Step Periodic Table (1928). This has a structure that shows a closer connection to the order of electron-shell filling and, by association, [[quantum mechanics]].<ref>{{cite journal |last=Scerri |first=E. |authorlink=Eric Scerri |title=The role of triads in the evolution of the periodic table: Past and present|journal=Journal of Chemical Education|year=2008|volume=85|issue=4|pages=585–589 (589)|doi=10.1021/ed085p585|bibcode = 2008JChEd..85..585S }}</ref> A somewhat similar approach has been taken by Alper,<ref>{{cite journal |last=Alper |first=R. |title=The simplified periodic table: elements ordered by their subshells|journal=The Journal of Biological Physics and Chemistry|year=2010|volume=10|issue=2|pages=74–80|doi=10.4024/43AL09F.jbpc.10.02}}</ref> albeit criticized by [[Eric Scerri]] as disregarding the need to display chemical and physical periodicity.<ref name="ScerriJBPC">{{cite journal |last=Scerri |first=E. |authorlink=Eric Scerri|title=Some comments on the recently proposed periodic table featuring elements ordered by their subshells|journal=Journal of Biological Physics and Chemistry|year=2012|volume=12|issue=2|pages=69–70}}</ref> Somewhere in the middle of the continuum is the ubiquitous common or standard form of periodic table. This is regarded as better expressing empirical trends in physical state, electrical and thermal conductivity, and oxidation numbers, and other properties easily inferred from traditional techniques of the chemical laboratory.<ref>{{cite journal |last1=Bent |first1=H. A. |last2=Weinhold |first2=F.|title=Supporting information: News from the periodic table: An introduction to "Periodicity symbols, tables, and models for higher-order valency and donor–acceptor kinships"|journal=Journal of Chemical Education|year=2007|volume=84|issue=7|pages=3–4|doi=10.1021/ed084p1145}}</ref> Its popularity is thought to be a result of this layout having a good balance of features in terms of ease of construction and size, and its depiction of atomic order and periodic trends.<ref name="Scerri 2011" /><ref>{{cite journal |last=Francl |first=M. |title=Table manners |journal=Nature Chemistry |volume=1 |date=May 2009 |pages=97–98 |url=http://ericscerri.com/Michelle-Nat%20Chem.pdf |bibcode=2009NatCh...1...97F |doi=10.1038/nchem.183 |issue=2 |pmid=21378810 |url-status=live |archiveurl=https://web.archive.org/web/20121025135145/http://ericscerri.com/Michelle-Nat%20Chem.pdf |archivedate=25 October 2012 |df=dmy-all }}</ref>
{{clear}}
{{periodic table (left step)}}
 
==Open questions and controversies==
 
===Placement of hydrogen and helium===
Simply following electron configurations, hydrogen (electronic configuration 1s<sup>1</sup>) and helium (1s<sup>2</sup>) should be placed in groups 1 and 2, above lithium (1s<sup>2</sup>2s<sup>1</sup>) and beryllium (1s<sup>2</sup>2s<sup>2</sup>).<ref name="Gray12">Gray, p. 12</ref> While such a placement is common for hydrogen, it is rarely used for helium outside of the context of electron configurations: When the [[noble gases]] (then called "inert gases") were first discovered around 1900, they were known as "group 0", reflecting no chemical reactivity of these elements known at that point, and helium was placed on the top of that group, as it did share the extreme chemical inertness seen throughout the group. As the group changed its formal number, many authors continued to assign helium directly above neon, in group 18; one of the examples of such placing is the current [[International Union of Pure and Applied Chemistry|IUPAC]] table.<ref>{{Cite web|url = http://www.iupac.org/fileadmin/user_upload/news/IUPAC_Periodic_Table-1May13.pdf|title = IUPAC Periodic Table of the Elements|date = 2013-05-01|accessdate = 2015-09-20|website = iupac.org|publisher = IUPAC|author = IUPAC|url-status=dead|archiveurl = https://web.archive.org/web/20150822234830/http://www.iupac.org/fileadmin/user_upload/news/IUPAC_Periodic_Table-1May13.pdf|archivedate = 22 August 2015|df = dmy-all}}</ref>
 
The position of hydrogen in group 1 is reasonably well settled. Its usual oxidation state is +1 as is the case for its heavier alkali metal congeners. Like lithium, it has a significant covalent chemistry.<ref>{{cite book|last=Cox|first=P. A.|title=Inorganic Chemistry|publisher=Bios Scientific|pages=[https://archive.org/details/inorganicchemist02edcoxp/page/149 149]|location=London|edition=2nd|isbn=978-1-85996-289-3|date=2004|url=https://archive.org/details/inorganicchemist02edcoxp/page/149}}</ref><ref>{{cite book |last1=Rayner-Canham|first1=G.|last2=Overton|first2=T.|title=Descriptive inorganic chemistry|publisher=W H Freeman|pages=203|location=New York|edition=4th|isbn=978-0-7167-8963-5|date=2006-01-01}}</ref>
It can stand in for alkali metals in typical alkali metal structures.<ref>{{cite web
|url=https://www.chemistryworld.com/news/hydrogen-adopts-alkali-metal-position/6769.article
|title=Hydrogen adopts alkali metal position
|last=Wilson
|first=P
|date=2013
|website=Chemistry World'
|publisher=Royal Society of Chemistry
|access-date=12 April 2019
|quote=
|archive-url=https://web.archive.org/web/20190412073023/https://www.chemistryworld.com/news/hydrogen-adopts-alkali-metal-position/6769.article
|archive-date=12 April 2019
|url-status=live
}}</ref> It is capable of forming alloy-like hydrides, featuring metallic bonding, with some transition metals.<ref>{{cite book |last=Bodner|first=G. M.|last2=Rickard|first2=L. H.|last3=Spencer|first3=J. N.|title=Chemistry: Structure and Dynamics|publisher=John Wiley & Son|page=101location=New York|isbn=978-0-471-14278-2|date=1995}}</ref>
 
Nevertheless, it is sometimes placed elsewhere. A common alternative is at the top of group 17<ref name="ScerriJBPC"/> given hydrogen's strictly univalent and largely non-metallic chemistry, and the strictly univalent and non-metallic chemistry of fluorine (the element otherwise at the top of group 17). Sometimes, to show hydrogen has properties corresponding to both those of the alkali metals and the halogens, it is shown at the top of the two columns simultaneously.<ref>{{cite journal |last=Seaborg |first= G.|title=The chemical and radioactive properties of the heavy elements |journal= Chemical & Engineering News|year=1945 |volume=23 |issue=23 |pages=2190–2193|doi= 10.1021/cen-v023n023.p2190}}</ref> Another suggestion is above carbon in group 14: placed that way, it fits well into the trends of increasing ionization potential values and electron affinity values, and is not too far from the electronegativity trend, even though hydrogen cannot show the [[tetravalence]] characteristic of the heavier group 14 elements.<ref name="hydrogen">{{cite journal |last=Cronyn |first=M. W. |title=The Proper Place for Hydrogen in the Periodic Table |journal=Journal of Chemical Education |volume=80 |issue=8 |date=August 2003 |pages=947–951|bibcode = 2003JChEd..80..947C |doi = 10.1021/ed080p947 }}</ref> Finally, hydrogen is sometimes placed separately from any group; this is based on its general properties being regarded as sufficiently different from those of the elements in any other group.
 
The other period 1 element, helium, is occasionally placed separately from any group as well.<ref>Greenwood & Earnshaw, throughout the book</ref> The property that distinguishes helium from the rest of the noble gases (even though the extraordinary inertness of helium is extremely close to that of neon and argon)<ref>{{Cite book|title = Modeling Marvels: Computational Anticipation of Novel Molecules|url = https://books.google.com/books?id=IoFzgBSSCwEC|publisher = Springer Science & Business Media|date = 2008-12-05|isbn = 978-1-4020-6973-4|first = Errol G.|last = Lewars|pages = 69–71|url-status=live|archiveurl = https://web.archive.org/web/20160519021952/https://books.google.com/books?id=IoFzgBSSCwEC|archivedate = 19 May 2016|df = dmy-all}}</ref> is that in its closed electron shell, helium has only two electrons in the outermost electron orbital, while the rest of the noble gases have eight.<!-- (Neon's electron configuration is [He]2s<sup>2</sup>2p<sup>6</sup>, argon's is [Ne]3s<sup>2</sup>3p<sup>6</sup>, and so on.)-->
 
==={{anchor|1=Period 6 and 7 elements in group 3}} Group 3 and its elements in periods 6 and 7 ===
Although scandium and yttrium are always the first two elements in group 3, the identity of the next two elements is not completely settled. They are commonly [[lanthanum]] and [[actinium]], and less often [[lutetium]] and [[lawrencium]]. The two variants originate from historical difficulties in placing the lanthanides in the periodic table, and arguments as to where the ''f'' block elements start and end.<ref>{{cite book|last=Thyssen|first=P.|last2=Binnemans|first2=K.|editor1-last=Gschneidner Jr.|editor1-first= K. A.|editor2-last=Bünzli|editor2-first=J-C.G|editor3-last=Vecharsky|editor3-first=Bünzli|date=2011|title=Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis|journal=Handbook on the Physics and Chemistry of Rare Earths|publisher=Elsevier|location=Amsterdam|volume=41|pages=1–94|isbn=978-0-444-53590-0|doi=10.1016/B978-0-444-53590-0.00001-7}}</ref>{{#tag:ref|But for the existence of the lanthanides the composition of group 3 would not have been a source of any special interest, since scandium, yttrium, lanthanum and actinium exhibit the same gradual change in properties as do calcium, strontium, barium and radium in group 2.<ref>{{cite book |last= Hevesy|first=G.|title= Redkie zemeli s tochki zreniya stroeniya atoma|trans-title=Rare earths from the point of view of structure of atom|year=1929|language=Russian|type=cited in Trifonov 1970, p.&nbsp;188|publisher= NKhTI|location=Leningrad}}</ref>|group=n}}{{#tag:ref|The detachment of the lanthanides from the main body of the periodic table has been attributed to the Czech chemist [[Bohuslav Brauner]] who, in 1902, allocated all of them ("Ce etc.") to one position in group 4, below zirconium. This arrangement was referred to as the "asteroid hypothesis", in analogy to asteroids occupying a single orbit in the solar system. Before this time the lanthanides were generally (and unsuccessfully) placed throughout groups I to VIII of the older 8-column form of periodic table. Although predecessors of Brauner's 1902 arrangement are recorded from as early as 1895, he is known to have referred to the "chemistry of asteroids" in an 1881 letter to Mendeleev. Other authors assigned all of the lanthanides to either group 3, groups 3 and 4, or groups 2, 3 and 4. In 1922 [[Niels Bohr]] continued the detachment process by locating the lanthanides between the s- and d-blocks. In 1949 [[Glenn T. Seaborg]] (re)introduced the form of periodic table that is popular today, in which the lanthanides and actinides appear as footnotes. Seaborg first published his table in a classified report dated 1944. It was published again by him in 1945 in ''[[Chemical and Engineering News]],'' and in the years up to 1949 several authors commented on, and generally agreed with, Seaborg's proposal. In that year he noted that the best method for presenting the actinides seemed to be by positioning them below, and as analogues of, the lanthanides. See: Thyssen P. and Binnemans K. (2011). "Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis". In K. A. Gschneider Jr. (ed). ''Handbook on the Physics and Chemistry of the Rare Earths.'' '''41'''. Amsterdam: Elsevier, pp. 1–94; Seaborg G. T. (1994). Origin of the Actinide Concept'. In K. A. Gschneider Jr. (ed). ''Handbook on the Physics and Chemistry of the Rare Earths''. '''18'''. Amsterdam: Elsevier, pp. 1–27.|group=n}} It has been claimed that such arguments are proof that, "it is a mistake to break the [periodic] system into sharply delimited blocks".<ref>{{cite journal |last=Stewart |first=P. J.|date=2008 |title=The Flyleaf Table: An Alternative|journal=Journal of Chemical Education|volume=85 |issue=11 |page=1490 |doi=10.1021/ed085p1490|bibcode = 2008JChEd..85.1490S }}</ref> A third variant shows the two positions below [[yttrium]] as being occupied by the lanthanides and the actinides. A fourth variant shows group 3 bifurcating after Sc-Y, into an La-Ac branch, and an Lu-Lr branch.<ref name="McGraw-Hill"/>
 
Chemical and physical arguments have been made in support of lutetium and lawrencium<ref>{{cite book |last1=Thyssen |first1=P. |last2=Binnemanns|first2=K. |editor-last1=Gschneidner Jr.|editor-first1=K. A. |editor-last2=Büzli |editor-first2=J-C. J.|editor-last3=Pecharsky |editor-first3=V. K.| title=Handbook on the Physics and Chemistry of Rare Earths | volume=41| publisher=Elsevier |date=2011 |pages=80–81|chapter=1: Accommodation of the rare earths in the periodic table: A historical analysis |isbn=978-0-444-53590-0|location=Amsterdam}}</ref><ref>{{cite book |last1=Keeler |first1=J. |last2=Wothers |first2=P. |publisher=Oxford University|location=Oxford |date=2014 |title=Chemical Structure and Reactivity: An Integrated Approach| isbn=978-0-19-960413-5|page=259}}</ref> but the majority of authors seem unconvinced.<ref name="finally">{{cite journal|last=Scerri|first=E.|authorlink=Eric Scerri|year=2012|journal=Chemistry International|volume=34|issue=4|url=http://www.iupac.org/publications/ci/2012/3404/ud.html|title=Mendeleev's Periodic Table Is Finally Completed and What To Do about Group 3?|url-status=live|archiveurl=https://web.archive.org/web/20170705051357/https://www.iupac.org/publications/ci/2012/3404/ud.html|archivedate=5 July 2017|df=dmy-all|doi=10.1515/ci.2012.34.4.28}}</ref> Most working chemists are not aware there is any controversy.<ref>{{Cite journal |url=http://www.nature.com/news/exotic-atom-struggles-to-find-its-place-in-the-periodic-table-1.17275 |title=Exotic atom struggles to find its place in the periodic table |last1=Castelvecchi |first1=D. |date=8 April 2015 |journal=Nature |access-date=20 Sep 2015 |url-status=live |archiveurl=https://web.archive.org/web/20151005164540/http://www.nature.com/news/exotic-atom-struggles-to-find-its-place-in-the-periodic-table-1.17275 |archivedate=5 October 2015 |df=dmy-all |doi=10.1038/nature.2015.17275 }}</ref> In December 2015 an [[International Union of Pure and Applied Chemistry|IUPAC]] project was established to make a recommendation on the matter.<ref>{{cite web|url=http://iupac.org/projects/project-details/?project_nr=2015-039-2-200|title=The constitution of group 3 of the periodic table|publisher=IUPAC|access-date=30 Jul 2016|date=2015|url-status=live|archiveurl=https://web.archive.org/web/20160705053631/http://iupac.org/projects/project-details/?project_nr=2015-039-2-200|archivedate=5 July 2016|df=dmy-all}}</ref>
 
====Lanthanum and actinium====
{| class="wikitable floatright" style="margin-left: 20px"
|-
|[[File:Periodic table 14CeTh form---Group 3 = Sc-Y-La-Ac.jpg|right|x100px]]<br /><small>La and Ac below Y</small>
|}
Lanthanum and actinium are commonly depicted as the remaining group 3 members.<ref>{{cite book |last=Emsley |first=J. |date=2011 |title=Nature's Building Blocks |publisher=Oxford University | edition=new|location =Oxford |isbn=978-0-19-960563-7|page=651}}</ref>{{#tag:ref|For examples of this table see [[P. W. Atkins|Atkins]] et al. (2006). ''Shriver & Atkins Inorganic Chemistry'' (4th ed.). Oxford: Oxford University Press • Myers et al. (2004). ''Holt Chemistry''. Orlando: Holt, Rinehart & Winston • [[Raymond Chang (chemist)|Chang R.]] (2000). ''Essential Chemistry'' (2nd ed.). Boston: McGraw-Hill|group=n}} It has been suggested that this layout originated in the 1940s, with the appearance of periodic tables relying on the electron configurations of the elements and the notion of the differentiating electron. The configurations of [[caesium]], [[barium]] and lanthanum are [Xe]6s<sup>1</sup>, [Xe]6s<sup>2</sup> and [Xe]5d<sup>1</sup>6s<sup>2</sup>. Lanthanum thus has a 5d differentiating electron and this establishes it "in group 3 as the first member of the d-block for period 6".<ref name=Jensen1982>{{cite journal |title=The Positions of Lanthanum (Actinium) and Lutetium (Lawrencium) in the Periodic Table |author=William B. Jensen |journal=J. Chem. Educ. |year=1982 |volume=59 |issue = 8|pages=634–636 |doi=10.1021/ed059p634|bibcode=1982JChEd..59..634J }}</ref> A consistent set of electron configurations is then seen in group 3: [[scandium]] [Ar]3d<sup>1</sup>4s<sup>2</sup>, yttrium [Kr]4d<sup>1</sup>5s<sup>2</sup> and lanthanum [Xe]5d<sup>1</sup>6s<sup>2</sup>. Still in period 6, [[ytterbium]] was assigned an electron configuration of [Xe]4f<sup>13</sup>5d<sup>1</sup>6s<sup>2</sup> and [[lutetium]] [Xe]4f<sup>14</sup>5d<sup>1</sup>6s<sup>2</sup>, "resulting in a 4f differentiating electron for lutetium and firmly establishing it as the last member of the f-block for period 6".<ref name=Jensen1982/> Later [[electron spectroscopy|spectroscopic]] work found that the electron configuration of ytterbium was in fact [Xe]4f<sup>14</sup>6s<sup>2</sup>. This meant that ytterbium and lutetium—the latter with [Xe]4f<sup>14</sup>5d<sup>1</sup>6s<sup>2</sup>—both had 14 f-electrons, "resulting in a d- rather than an f- differentiating electron" for lutetium and making it an "equally valid candidate" with [Xe]5d<sup>1</sup>6s<sup>2</sup> lanthanum, for the group 3 periodic table position below yttrium.<ref name=Jensen1982/> Lanthanum has the advantage of incumbency since the 5d<sup>1</sup> electron appears for the first time in its structure whereas it appears for the third time in lutetium, having also made a brief second appearance in gadolinium.<ref name=Trifonov>{{cite book |last=Trifonov|first1=D. N.|
title= Rare-earth elements and their position in the periodic system|type=translated from Russian|year=1970|pages=201–202|publisher=Indian National Scientific Documentation Centre|location=New Delhi}}</ref>
 
In terms of chemical behaviour,<ref name=Harrington>{{cite book |last1=Greenwood|first1=N. N.|last2=Harrington|first2=T. J.|title=The chemistry of the transition elements|year=1973|page=50|publisher=Clarendon Press|location=Oxford|isbn=978-0-19-855435-6}}</ref> and trends going down group 3 for properties such as melting point, electronegativity and ionic radius,<ref name= Aylward>{{cite book |last1= Aylward |first1=G.|last2= Findlay |first2=T.|title=SI chemical data|year=2008|publisher=John Wiley & Sons|location=Milton, Queensland|edition=6th|isbn=978-0-470-81638-7}}</ref><ref name=Wiberg>{{cite book |last=Wiberg|first1=N.|title= Inorganic Chemistry|year=2001|page=119|publisher=Academic Press
|isbn=978-0-12-352651-9|location=San Diego}}</ref> scandium, yttrium, lanthanum and actinium are similar to their group 1–2 counterparts. In this variant, the number of ''f'' electrons in the most common (trivalent) ions of the f-block elements consistently matches their position in the f-block.<ref name=Wulfsberg>{{cite book |last=Wulfsberg|first1=G.|article=Periodic table: Trends in the properties of the elements|title= Encyclopedia of Inorganic Chemistry|year=2006|page=3|publisher=John Wiley & Sons|location=New York|isbn=978-0-470-86210-0}}</ref> For example, the f-electron counts for the trivalent ions of the first three f-block elements are Ce 1, Pr 2 and Nd 3.<ref name=Cotton>{{cite book |last=Cotton|first=S.|title= Lanthanide and Actinide Chemistry|year=2007|page=150|publisher=John Wiley & Sons|location=Chichester|isbn=978-0-470-01006-8}}</ref>
 
====Lutetium and lawrencium====
{| class="wikitable floatright" style="margin-left: 20px"
|-
||[[File:Periodic table 14LaAc form---Group 3 = Sc-Y-Lu-Lr.jpg|right|x100px]]<br /><small>Lu and Lr below Y</small>
|}
In other tables, lutetium and lawrencium are the remaining group 3 members.{{#tag:ref|For examples of the group 3 = Sc-Y-Lu-Lr table see Rayner-Canham G. & Overton T. (2013). ''Descriptive Inorganic Chemistry'' (6th ed.). New York: W. H. Freeman and Company • Brown et al. (2009). ''Chemistry: The Central Science'' (11th ed.). Upper Saddle River, New Jersey: Pearson Education • Moore et al. (1978). ''Chemistry''. Tokyo: McGraw-Hill Kogakusha|group=n}} Early techniques for chemically separating scandium, yttrium and lutetium relied on the fact that these elements occurred together in the so-called "yttrium group" whereas La and Ac occurred together in the "cerium group".<ref name=Jensen1982/> Accordingly, lutetium rather than lanthanum was assigned to group 3 by some chemists in the 1920s and 30s.{{#tag:ref|The phenomenon of different separation groups is caused by increasing basicity with increasing radius, and does not constitute a fundamental reason to show Lu, rather than La, below Y. Thus, among the Group 2 [[alkaline earth metal]]s, Mg (less basic) belongs in the "soluble group" and Ca, Sr and Ba (more basic) occur in the "ammonium carbonate group". Nevertheless, Mg, Ca, Sr and Ba are routinely collocated in Group 2 of the periodic table. See: Moeller et al. (1989). ''Chemistry with Inorganic Qualitative Analysis'' (3rd ed.). SanDiego: Harcourt Brace Jovanovich, pp.&nbsp;955–956, 958.|group=n}} Several physicists in the 1950s and '60s favoured lutetium, in light of a comparison of several of its physical properties with those of lanthanum.<ref name=Jensen1982/> This arrangement, in which lanthanum is the first member of the f-block, is disputed by some authors since lanthanum lacks any f-electrons. It has been argued that this is not a valid concern given other periodic table anomalies—thorium, for example, has no f-electrons yet is part of the f-block.<ref>{{cite magazine|url= https://eic.rsc.org/opinion/five-ideas-in-chemical-education-that-must-die-part-five/2010032.article|title= Five ideas in chemical education that must die – Group three |last1= Scerri|first1= E.|date=15 September 2015| magazine=[[Education in Chemistry]] |publisher=[[Royal Society of Chemistry]]|access-date= Sep 19, 2015|quote= It is high time that the idea of group 3 consisting of Sc, Y, La and Ac is abandoned|url-status=live|archiveurl= https://web.archive.org/web/20151223190417/http://www.rsc.org/blogs/eic/2015/09/periodic-table-group-3|archivedate= 23 December 2015|df= dmy-all}}</ref> As for lawrencium, its gas phase atomic electron configuration was confirmed in 2015 as [Rn]5f<sup>14</sup>7s<sup>2</sup>7p<sup>1</sup>. Such a configuration represents another periodic table anomaly, regardless of whether lawrencium is located in the f-block or the d-block, as the only potentially applicable p-block position has been reserved for nihonium with its predicted configuration of [Rn]5f<sup>14</sup>6d<sup>10</sup>7s<sup>2</sup>7p<sup>1</sup>.<ref name=Jensen2015>{{cite web|url=http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/251.%20Lawrencium.pdf |title=Some Comments on the Position of Lawrencium in the Periodic Table |last1=Jensen |first1=W. B. |date=2015 |access-date=20 Sep 2015 |url-status=dead |archiveurl=https://web.archive.org/web/20151223091325/http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/251.%20Lawrencium.pdf |archivedate=23 December 2015 |df= }}</ref>{{#tag:ref|Even if metallic lawrencium has a'' p'' electron, simple modelling studies suggest it will behave like a lanthanide,<ref name=Xu>{{cite journal |last1=Xu |first1=W-H. |last2= Pyykkö|first2=P.|title=Is the chemistry of lawrencium peculiar? |journal=Physical Chemistry Chemical Physics |year=2016 |volume=18 |issue=26 |pages=17351–17355|doi=10.1039/C6CP02706G|pmid=27314425 |bibcode=2016PCCP...1817351X|hdl=10138/224395 |url=https://helda.helsinki.fi/bitstream/10138/224395/1/c6cp02706g.pdf }}</ref> as do the rest of the late actinides.<ref name=Cotton/>|group=n}}
 
Chemically, scandium, yttrium and lutetium (and presumably lawrencium) behave like trivalent versions of the group 1–2 metals.<ref name=King>{{cite book|last=King|first=R. B.|title= Inorganic Chemistry of Main Group Elements|year=1995|page=289|publisher=Wiley-VCH|location=New York|isbn=978-1-56081-679-9}}</ref> On the other hand, trends going down the group for properties such as melting point, electronegativity and ionic radius, are similar to those found among their group 4–8 counterparts.<ref name=Jensen1982/> In this variant, the number of ''f'' electrons in the gaseous forms of the f-block atoms usually matches their position in the f-block. For example, the f-electron counts for the first five f-block elements are La 0, Ce 1, Pr 3, Nd 4 and Pm 5.<ref name=Jensen1982/>
 
====Lanthanides and actinides====
{| class="wikitable floatright" style="margin-left: 20px"
|-
|[[File:Periodic table 15LaAc form---Group 3 = indeterminate.jpg|right|x100px]]<br /><small>Markers below Y</small>
|}
A few authors position all thirty lanthanides and actinides in the two positions below yttrium (usually via footnote markers).
This variant, which is stated in the 2005 ''[[IUPAC nomenclature of inorganic chemistry#Nomenclature of Inorganic Chemistry|Red Book]]'' to be the IUPAC-agreed version as of 2005 (a number of later versions exist, and the last update is from 1st Dec. 2018),<ref>{{cite book|title=Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005|last1=Connelly|first1=N. G.|last2=Damhus|first2=T.|last3=Hartshorn|first3=R. M.|last4=Hutton|first4=A. T.|year=2005|publisher=RSC Publishing|isbn=978-0-85404-438-2|page=vii|url=https://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf|quote=Lesser omissions include ... the several different outdated versions of the periodic table. (That on the inside front cover is the current IUPAC-agreed version.)|access-date=26 November 2018|archive-url=https://web.archive.org/web/20181123034019/http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf|archive-date=23 November 2018|url-status=live}}</ref>{{#tag:ref|Notwithstanding, an IUPAC member subsequently wrote that, "IUPAC has not approved any specific form of the periodic table, and an IUPAC-approved form does not exist, though even members of IUPAC themselves have published diagrams titled “IUPAC Periodic Table of the Elements". However, the only specific recommendation IUPAC has made concerning the periodic table covers the Group numbering of 1–18."<ref>{{cite journal |last=Leigh |first=G. J. |year=2009 |title=Periodic Tables and IUPAC |journal=[[Chemistry International]] |volume=31 |issue=1 |url=https://old.iupac.org/publications/ci/2009/3101/1_leigh.html |accessdate=27 November 2018 |doi=10.1515/ci.2009.31.1.4 |archive-url=https://web.archive.org/web/20181127022628/https://old.iupac.org/publications/ci/2009/3101/1_leigh.html |archive-date=27 November 2018 |url-status=live }}</ref>|group=n}} emphasizes similarities in the chemistry of the 15 lanthanide elements (La–Lu), possibly at the expense of ambiguity as to which elements occupy the two group 3 positions below yttrium, and a 15-column wide ''f'' block (there can only be 14 elements in any row of the ''f'' block).{{#tag:ref|For examples of the group 3 = Ln and An table see Housecroft C. E. & Sharpe A. G. (2008). ''Inorganic Chemistry'' (3rd ed.). Harlow: Pearson Education • Halliday et al. (2005). ''Fundamentals of Physics'' (7th ed.). Hoboken, NewJersey: John Wiley & Sons • Nebergall et al. (1980). ''General Chemistry'' (6th ed.). Lexington: D. C. Heath and Company|group=n}}
 
====La-Ac and Lu-Lr====
[[File:Silberberg style periodic table.png|thumb|32-column periodic table, with bifurcated group 3]]
In this variant, group 3 bifurcates after Sc-Y into a La-Ac branch, and a Lu-Lr branch. This arrangement is consistent with the hypothesis that arguments in favour of either Sc-Y-La-Ac or Sc-Y-Lu-Lr based on chemical and physical data are inconclusive.<ref>{{cite book|last=Scerri|first=P.|last2=Parsons|first2=B.|editor1-last=Scerri|editor1-first= E.|editor2-last=Restrepo|editor2-first=G.|date=2018|title=From Mendeleev to Oganesson: A Multidisciplinary Perspective on the Periodic Table|chapter=What elements belong in group 3 of the Periodic Table?|publisher=Oxford University Press|location=New York|pages=140–151|isbn=978-0-190-66853-2}}</ref> As noted, trends going down Sc-Y-La-Ac match trends in groups 1−2<ref>{{cite book |last1=Lee|first=J. D.|title= Concise inorganic chemistry |year=1996|page=679|publisher=Blackwell-Science|location=Oxford|edition=5th|isbn=978-0-6320-5293-6}}</ref> whereas trends going down Sc-Y-Lu-Lr better match trends in groups 4−10.<ref name=Jensen1982/>
 
===Groups included in the transition metals===
The definition of a [[transition metal]], as given by IUPAC, is an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell.<ref name="ReferenceA">{{GoldBookRef|file=T06456|title=transition element}}</ref> By this definition all of the elements in groups 3–11 are transition metals. The IUPAC definition therefore excludes group 12, comprising zinc, cadmium and mercury, from the transition metals category.
 
Some chemists treat the categories "[[d-block]] elements" and "transition metals" interchangeably, thereby including groups 3–12 among the transition metals. In this instance the group 12 elements are treated as a special case of transition metal in which the d electrons are not ordinarily involved in chemical bonding. The 2007 report of [[mercury(IV) fluoride]] (HgF<sub>4</sub>), a compound in which mercury would use its d electrons for bonding, has prompted some commentators to suggest that mercury can be regarded as a transition metal.<ref>{{cite journal |last1=Xuefang|first1= W. |last2=Andrews|first2=L.|last3=Riedel|first3=S.|last4= Kaupp|first4=M. |title=Mercury Is a Transition Metal: The First Experimental Evidence for HgF<sub>4</sub> |journal=Angew. Chem. Int. Ed. |year=2007 |volume=46 |issue=44 |pages=8371–8375 |doi=10.1002/anie.200703710 |pmid=17899620}}</ref> Other commentators, such as Jensen,<ref name=Jensen2008>{{cite journal |title=Is Mercury Now a Transition Element? |last = Jensen |first= W. B.|journal=J. Chem. Educ. |year=2008 |volume=85 |pages=1182–1183 |doi=10.1021/ed085p1182|bibcode = 2008JChEd..85.1182J |issue=9 }}</ref> have argued that the formation of a compound like HgF<sub>4</sub> can occur only under highly abnormal conditions; indeed, its existence is currently disputed. As such, mercury could not be regarded as a transition metal by any reasonable interpretation of the ordinary meaning of the term.<ref name=Jensen2008/>
 
Still other chemists further exclude the [[group 3 element]]s from the definition of a transition metal. They do so on the basis that the group 3 elements do not form any ions having a partially occupied d shell and do not therefore exhibit any properties characteristic of transition metal chemistry.<ref>{{cite book |last1=Rayner-Canham|first1=G.|last2=Overton|first2=T.|title=Descriptive inorganic chemistry|publisher=W H Freeman|pages=484–485|location=New York|edition=4th|isbn=978-0-7167-8963-5|date=2006-01-01}}</ref> In this case, only groups 4–11 are regarded as transition metals. Though the group 3 elements show few of the characteristic chemical properties of the transition metals, they do show some of their characteristic physical properties (on account of the presence in each atom of a single d electron).<ref name=Greenwood947>Greenwood & Earnshaw, p. 947</ref>
 
===Elements with unknown chemical properties===
Although all elements up to oganesson have been discovered, of the elements above [[hassium]] (element 108), only [[copernicium]] (element 112), [[nihonium]] (element 113), and [[flerovium]] (element 114) have known chemical properties, and only for copernicium is there enough evidence for a conclusive categorisation at present. The other elements may behave differently from what would be predicted by extrapolation, due to [[relativistic quantum chemistry|relativistic]] effects; for example, flerovium has been predicted to possibly exhibit some noble-gas-like properties, even though it is currently placed in the [[carbon group]].<ref>{{cite book|title=The Chemistry of Superheavy Elements|last=Schändel|first=M.|year=2003|publisher=Kluwer Academic Publishers|location=Dordrecht|isbn=978-1-4020-1250-1|page=277}}</ref> The current experimental evidence still leaves open the question of whether flerovium behaves more like a metal or a noble gas.<ref>{{cite conference |url=http://www.epj-conferences.org/articles/epjconf/pdf/2016/26/epjconf-NS160-07003.pdf |title=Gas-phase chemistry of element 114, flerovium |last1=Yakushev |first1=Alexander |last2=Eichler |first2=Robert |date=2016 |conference=Nobel Symposium NS160 – Chemistry and Physics of Heavy and Superheavy Elements |doi=10.1051/epjconf/201613107003 |access-date=3 April 2018 |archive-url=https://web.archive.org/web/20170331024824/http://www.epj-conferences.org/articles/epjconf/pdf/2016/26/epjconf-NS160-07003.pdf |archive-date=31 March 2017 |url-status=live }}</ref>
 
===Further periodic table extensions===
{{main|Extended periodic table}}
<div style="float: right; margin-left: 20px; font-size:85%;">
{{Periodic table (micro)|number=120|caption=Periodic table with eight rows, extended to element 172<ref name="Fricke">{{cite journal |last1=Fricke |first1=B. |last2=Greiner |first2=W. |last3=Waber |first3=J. T. |year=1971 |title=The continuation of the periodic table up to Z = 172. The chemistry of superheavy elements |journal=Theoretica Chimica Acta |volume=21 |issue=3 |pages=235–260 |doi=10.1007/BF01172015|url=https://www.semanticscholar.org/paper/41001c5ccd4c803c9425e691d582f10632f65cec }}</ref>}}
</div>
It is unclear whether new elements will continue the pattern of the current periodic table as [[Period 8 element|period 8]], or require further adaptations or adjustments. [[Glenn T. Seaborg|Seaborg]] expected the eighth period to follow the previously established pattern exactly, so that it would include a two-element s-block for elements [[ununennium|119]] and [[unbinilium|120]], a new [[g-block]] for the next 18 elements, and 30 additional elements continuing the current f-, d-, and p-blocks, culminating in element 168, the next noble gas.<ref>{{cite journal|doi=10.2307/3963006|last=Frazier|first=K.|title=Superheavy Elements|journal=Science News|volume=113|issue=15|pages=236–238|year=1978|jstor=3963006}}</ref> More recently, physicists such as [[Pekka Pyykkö]] have theorized that these additional elements do not follow the [[Madelung rule]], which predicts how electron shells are filled and thus affects the appearance of the present periodic table. There are currently several competing theoretical models for the placement of the elements of atomic number less than or equal to 172. In all of these it is element 172, rather than element 168, that emerges as the next noble gas after oganesson, although these must be regarded as speculative as no complete calculations have been done beyond element 123.<ref>{{Cite journal|last1=Pyykkö|first1=P.|authorlink=Pekka Pyykkö|title=A suggested periodic table up to Z ≤ 172, based on Dirac–Fock calculations on atoms and ions|journal=Physical Chemistry Chemical Physics|volume=13|issue=1|pages=161–168|year=2011|pmid=20967377|doi=10.1039/c0cp01575j|bibcode = 2011PCCP...13..161P|url=https://semanticscholar.org/paper/a0ec522315904230d171353561d53f24d17dcfad}}</ref><ref name=e123>{{cite thesis|last=van der Schoor|first=K.|title=Electronic structure of element 123|url=http://fse.studenttheses.ub.rug.nl/14531/1/report.pdf|date=2016|publisher=Rijksuniversiteit Groningen|accessdate=24 February 2019|archiveurl=https://web.archive.org/web/20190113003943/http://fse.studenttheses.ub.rug.nl/14531/1/report.pdf|archivedate=13 January 2019|url-status=live}}</ref>
 
===Element with the highest possible atomic number===
The number of possible elements is not known. A very early suggestion made by Elliot Adams in 1911, and based on the arrangement of elements in each horizontal periodic table row, was that elements of atomic weight greater than circa 256 (which would equate to between elements 99 and 100 in modern-day terms) did not exist.<ref>{{cite journal |last=Elliot|first=Q. A. |title=A modification of the periodic table|journal=Journal of the American Chemical Society|year=1911|volume=33 |issue=5 |pages=684–688 (688)|doi=10.1021/ja02218a004|url=https://zenodo.org/record/1429013 }}</ref> A higher, more recent estimate is that the periodic table may end soon after the [[island of stability]],<ref name=EB>{{cite encyclopedia|last1=Seaborg|first1=G.|url=http://www.britannica.com/EBchecked/topic/603220/transuranium-element|title=transuranium element (chemical element)|encyclopedia=Encyclopædia Britannica|date=c. 2006|accessdate=16 March 2010|url-status=live|archiveurl=https://web.archive.org/web/20101130112151/http://www.britannica.com/EBchecked/topic/603220/transuranium-element|archivedate=30 November 2010|df=dmy-all}}</ref> whose centre is predicted to lie between [[darmstadtium|element 110]] and [[unbihexium|element 126]], as the extension of the periodic and [[table of nuclides|nuclide tables]] is restricted by proton and neutron [[Nuclear drip line|drip lines]] as well as decreasing stability towards [[spontaneous fission]].<ref>{{cite journal | first1=S.|last1=Cwiok|first2= P.-H.|last2= Heenen |first3= W.|last3= Nazarewicz |year=2005|title=Shape coexistence and triaxiality in the superheavy nuclei|journal=Nature|volume=433|bibcode = 2005Natur.433..705C |doi = 10.1038/nature03336 | issue=7027 | pmid=15716943 | pages=705–9|url=https://www.semanticscholar.org/paper/b4c38cdf576a097c956b3ab413d0498af6202da7}}</ref><ref name=quest>{{cite journal|last=Bemis|first=C. E.|last2=Nix|first2=J. R.|date=1977|title=Superheavy elements - the quest in perspective|journal=Comments on Nuclear and Particle Physics|volume=7|issue=3|pages=65–78|url=http://inspirehep.net/record/1382449/files/v7-n3-p65.pdf|issn=0010-2709}}</ref> Other predictions of an end to the periodic table include at element 128 by [[John Emsley]],<ref name="emsley"/> at element 137 by [[Richard Feynman]],<ref name="rscend" /> at element 146 by Yogendra Gambhir,<ref name=limit146>{{cite journal|last=Gambhir|first=Y.K|last2=Bhagwat|first2=A.|last3=Gupta|first3=M.|title=The highest limiting Z in the extended periodic table|date=2015|journal=Journal of Physics G: Nuclear and Particle Physics|volume=42|issue=12|pages=125105|doi=10.1088/0954-3899/42/12/125105|url= https://www.researchgate.net/publication/284213926|bibcode=2015JPhG...42l5105G}}</ref> and at element 155 by Albert Khazan.<ref name="emsley"/>{{#tag:ref|Karol (2002, p.&nbsp;63) contends that gravitational effects would become significant when atomic numbers become astronomically large, thereby overcoming other super-massive nuclei instability phenomena, and that [[neutron star]]s (with atomic numbers on the order of 10<sup>21</sup>) can arguably be regarded as representing the heaviest known elements in the universe. See: Karol P. J. (2002). "The Mendeleev–Seaborg periodic table: Through Z = 1138 and beyond". ''Journal of Chemical Education'' '''79''' (1): 60–63.|group=n}}
 
====Bohr model====
The [[Bohr model]] exhibits difficulty for atoms with atomic number greater than 137, as any element with an atomic number greater than 137 would require 1s electrons to be travelling faster than ''c'', the [[speed of light]].<ref>{{cite book
|first1=R. |last1=Eisberg|first2= R.|last2= Resnick
|year=1985
|title=Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles
|url=https://archive.org/details/quantumphysicsof00eisb |url-access=registration |publisher=[[John Wiley & Sons|Wiley]]
|isbn=
}}</ref> Hence the non-relativistic Bohr model is inaccurate when applied to such an element.
 
====Relativistic Dirac equation====
The [[Theory of relativity|relativistic]] [[Dirac equation]] has problems for elements with more than 137 protons. For such elements, the wave function of the Dirac ground state is oscillatory rather than bound, and there is no gap between the positive and negative energy spectra, as in the [[Klein paradox]].<ref>
{{cite book
|first1=J. D.|last1= Bjorken|first2=S. D.|last2= Drell
|year=1964
|title=Relativistic Quantum Mechanics
|url=https://archive.org/details/relativisticquan0000bjor|url-access=registration|publisher=[[McGraw-Hill]]
|isbn=
}}</ref> More accurate calculations taking into account the effects of the finite size of the nucleus indicate that the binding energy first exceeds the limit for elements with more than 173 protons. For heavier elements, if the innermost orbital (1s) is not filled, the electric field of the nucleus will pull an electron out of the vacuum, resulting in the [[Positron emission|spontaneous emission of a positron]].<ref>
{{cite journal
|first1=W. |last1=Greiner|first2= S. |last2=Schramm
|year=2008
|journal=[[American Journal of Physics]]
|volume=76 |issue=6|pages=509
|doi=10.1119/1.2820395
|title=Resource Letter QEDV-1: The QED vacuum
|bibcode=2008AmJPh..76..509G}}, and references therein.</ref> This does not happen if the innermost orbital is filled, so that element 173 is not necessarily the end of the periodic table.<ref name="rscend">{{cite journal|last=Ball|first=P.|authorlink=Philip Ball|journal=[[Chemistry World]]|url=http://www.rsc.org/chemistryworld/Issues/2010/November/ColumnThecrucible.asp|title=Would Element 137 Really Spell the End of the Periodic Table? Philip Ball Examines the Evidence|date=November 2010|accessdate=30 September 2012|url-status=live|archiveurl=https://web.archive.org/web/20121021020542/http://www.rsc.org/chemistryworld/Issues/2010/November/ColumnThecrucible.asp|archivedate=21 October 2012|df=dmy-all}}</ref>
 
===Optimal form===
The many different forms of periodic table have prompted the question of whether there is an optimal or definitive form of periodic table.<ref name=optimal/> The answer to this question is thought to depend on whether the chemical periodicity seen to occur among the elements has an underlying truth, effectively hard-wired into the universe, or if any such periodicity is instead the product of subjective human interpretation, contingent upon the circumstances, beliefs and predilections of human observers. An objective basis for chemical periodicity would settle the questions about the location of hydrogen and helium, and the composition of group 3. Such an underlying truth, if it exists, is thought to have not yet been discovered. In its absence, the many different forms of periodic table can be regarded as variations on the theme of chemical periodicity, each of which explores and emphasizes different aspects, properties, perspectives and relationships of and among the elements.{{#tag:ref|[[Eric Scerri|Scerri]], one of the foremost authorities on the history of the periodic table,<ref>{{cite journal|last = Sella|first = Andrea|authorlink = Andrea Sella|url = https://www.newscientist.com/article/mg21929291-200-an-elementary-history-lesson/|title = An elementary history lesson|journal = [[New Scientist]]|volume = 219|date = 7 August 2013|issue = 2929|pages = 51|accessdate = 13 June 2017|url-status=live|archiveurl = https://web.archive.org/web/20160703041107/https://www.newscientist.com/article/mg21929291-200-an-elementary-history-lesson|archivedate = 3 July 2016|df = dmy-all|doi = 10.1016/S0262-4079(13)62001-1|bibcode = 2013NewSc.219...51S}}</ref> whilst previously recognising the value of a plurality of periodic tables,<ref name=optimal>{{cite web|first = Eric|last = Scerri|authorlink = Eric Scerri|date = 9 August 2013|url = http://ericscerri23.blogspot.com.au/2013/08/0-0-1-16-77-ucla-2-1-92-14.html|title = Is there an optimal periodic table and other bigger questions in the philosophy of science|accessdate = 4 September 2013|publisher = [[Eric Scerri]]|website = ericscerri23.blogspot.com.au|url-status=live|archiveurl = https://web.archive.org/web/20170613022703/http://ericscerri23.blogspot.com.au/2013/08/0-0-1-16-77-ucla-2-1-92-14.html|archivedate = 13 June 2017|df = dmy-all}}</ref> currently supports the concept of an optimal table.<ref>{{cite web
|url=https://blog.oup.com/2019/01/happy-sesquicentennial-periodic-table-elements/
|title=Happy sesquicentennial to the periodic table of the elements
|last=Scerri
|first=Eric
|date=29 January 2019
|website=
|publisher=Oxford University Press
|access-date=12 April 2019
|quote=
|archive-url=https://web.archive.org/web/20190327082337/https://blog.oup.com/2019/01/happy-sesquicentennial-periodic-table-elements/
|archive-date=27 March 2019
|url-status=live
}}</ref>|group=n}}
 
== Other ==
In celebration of the periodic table's 150th anniversary, the [[United Nations]] declared the year 2019 as the International Year of the Periodic Table, celebrating "one of the most significant achievements in science".<ref name=":1">{{Cite news|url=https://www.bbc.com/news/science-environment-47008289|title=Happy birthday, periodic table|last=Briggs|first=Helen|date=2019-01-29|access-date=2019-02-08|language=en-GB|archive-url=https://web.archive.org/web/20190209210210/https://www.bbc.com/news/science-environment-47008289|archive-date=9 February 2019|url-status=live}}</ref>
 
==See also==
{{Portal|Chemistry}}
{{Wikipedia books|Periodic table}}
{{div col|colwidth=30em}}
* [[Abundance of the chemical elements]]
* [[Atomic electron configuration table]]
* [[Element collecting]]
* [[List of chemical elements]]
* [[List of periodic table-related articles]]
* [[Names for sets of chemical elements]]
* [[Standard model]]
* [[Table of nuclides]]
* [[Template:Spectral lines of the elements]]
* [[The Mystery of Matter (film)|''The Mystery of Matter: Search for the Elements'' (PBS film)]]
* [[Timeline of chemical element discoveries]]
{{div col end}}
 
==Notes==
{{reflist|group="n"}}
 
==References==
{{Reflist}}
 
===Bibliography===
{{refbegin}}
* {{cite book|last=Ball|first=P.|authorlink=Philip Ball|title=The Ingredients: A Guided Tour of the Elements |location=Oxford|publisher=Oxford University Press |year=2002 |isbn=978-0-19-284100-1}}
* {{cite book|last=Chang|first=R.|authorlink=Raymond Chang (chemist)|title=Chemistry|url=https://archive.org/details/riimchemistry00chan|url-access=registration|year=2002|edition=7th|publisher=McGraw-Hill Higher Education|location=New York|isbn=978-0-19-284100-1}}
* {{cite book|last=Gray|first=T.|authorlink=Theodore Gray|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}}
* {{cite book|last1=Greenwood|first1=N. N.|authorlink1=Norman Greenwood|last2=Earnshaw|first2=A.|year=1984|title=Chemistry of the Elements|place=Oxford|publisher=Pergamon Press|isbn=978-0-08-022057-4}}
* {{cite book|last1=Huheey|first1=J. E.|last2=Keiter|first2=E. A.|last3=Keiter|first3=R. L.|title=Principles of structure and reactivity|publisher=Harper Collins College Publishers|location=New York|edition=4th|isbn=978-0-06-042995-9|url=https://archive.org/details/inorganicchemist00huhe_0|year=1993}}
* {{cite book |last=Moore |first=J. T.|edition=1st|title=Chemistry For Dummies|series = [[For Dummies]] |year=2003 |publisher=Wiley Publications |location=New York |isbn=978-0-7645-5430-8}}
* {{cite book|last=Scerri |first=E.|authorlink=Eric Scerri|title=The periodic table: Its story and its significance|url=https://archive.org/details/periodictableits0000scer |url-access=registration |publisher=Oxford University Press|location=Oxford|year=2007|isbn=978-0-19-530573-9}}
* {{cite book |last=Scerri|first=E.|authorlink=Eric Scerri|title=The periodic table: A very short introduction|year=2011|publisher=Oxford University Press|location=Oxford|isbn=978-0-19-958249-5}}
* {{cite book |last=Venable|first=F. P.|authorlink=Francis Preston Venable|title=The Development of the Periodic Law|year=1896|url=https://books.google.com/books?id=tF0vAQAAMAAJ|publisher=Chemical Publishing Company|location=Easton, Pennsylvania|oclc=776059614}}
{{refend}}
 
==Further reading==
{{refbegin}}
* {{cite book |last=Calvo |first=Miguel |year=2019 |title= Construyendo la Tabla Periódica|chapter=|pages=407|location=Zaragoza, Spain |publisher=Prames |edition=|isbn=978-84-8321-908-9|author-link=}}
* {{cite book |last=Emsley |first=J. |year=2011 |title=Nature's Building Blocks: An A–Z Guide to the Elements |chapter=The Periodic Table|pages=634–651|location=Oxford |publisher=Oxford University Press |edition=New|isbn=978-0-19-960563-7 |author-link=John Emsley }}
* {{cite book |first1=Marco |last1=Fontani |first2=Mariagrazia |last2=Costa |first3=Mary Virginia |last3=Orna |year=2007 |title=The Lost Elements: The Periodic Table's Shadow Side |url= |chapter=|pages=508|location=Oxford|publisher= Oxford University Press |edition=|isbn=978-0-19-938334-4|author-link=}}
* {{cite book |last=Mazurs |first=E. G.|year=1974 |title=Graphical Representations of the Periodic System During One Hundred Years |url= |chapter=|location=Alabama |publisher=University of Alabama Press |edition=|isbn=978-0-19-960563-7 |author-link=John Emsley }}
* {{cite conference |first1=D.H. |last1=Rouvray |first2=R. B. (eds) |last2=King |title=The Periodic Table: Into the 21st Century |publisher= Research Studies Press |location=Baldock, Hertfordshire|conference=Proceedings of the 2nd International Conference on the Periodic Table, part 1, Kananaskis Guest Ranch, Alberta, 14–20 July 2003 |isbn=978-0-86380-292-8 |year=2004}}
* {{cite conference |first1=D.H. |last1=Rouvray |first2=R. B. (eds) |last2=King |title=The Mathematics of the Periodic Table |publisher= Nova Science |location=New York|conference=Proceedings of the 2nd International Conference on the Periodic Table, part 2, Kananaskis Guest Ranch, Alberta, 14–20 July 2003 |isbn=978-1-59454-259-6 |year=2006}}
* {{cite web |url=http://www.ericscerri.com/books_elements.pdf |title=Books on the Elements and the Periodic Table |last=Scerri |first=E
|date=n.d. |website= |access-date=9 July 2018 |quote= }}
* {{cite conference |first1=E. |last1=Scerri |first2=G (eds) |last2=Restrepo |title=Mendeleev to Oganesson: A Multidisciplinary Perspective on the Periodic Table |publisher= Oxford University Press |location=Oxford|conference=Proceedings of the 3rd International Conference on the Periodic Table, Cuzco, Peru 14–16 August 2012 |isbn=978-0-86380-292-8 |year=2018}}
* {{cite book|last=van Spronsen|first=J. W.|authorlink=|title=The Periodic System of Chemical Elements: A History of the First Hundred Years |location=Amsterdam|publisher=Elsevier |year=1969 |isbn=978-0-444-40776-4}}
* {{cite conference |first=M. (ed.) |last=Verde |title= Atti del convegno Mendeleeviano: Periodicità e simmetrie nella struttura elementare della materia |publisher=Accademia delle Scienze di Torino |location=Torino |trans-title=Proceedings of the Mendeleevian conference: Periodicity and symmetry in the elementary structure of matter|conference=1st International Conference on the Periodic Table, Torino-Roma, 15–21 September 1969|year=1971}}
{{refend}}
 
==External links==
{{Sister project links|Periodic table}}
* [https://digital.sciencehistory.org/focus/periodic-tables Periodic Table] featured topic page on [[Science History Institute]] [https://digital.sciencehistory.org/ Digital Collections] featuring select visual representations of the periodic table of the elements, with an emphasis on alternative layouts including circular, cylindrical, pyramidal, spiral, and triangular forms.
* [http://iupac.org/what-we-do/periodic-table-of-elements IUPAC Periodic Table of the Elements]
* [http://www.ptable.com Dynamic periodic table], with interactive layouts
* [http://ericscerri.com/ Eric Scerri], leading philosopher of science specializing in the history and philosophy of the periodic table
* [http://www.meta-synthesis.com/webbook//35_pt/pt_database.php The INTERNET Database of Periodic Tables]
* [https://web.archive.org/web/20180112160406/https://www.acs.org/content/acs/en/greenchemistry/research-innovation/research-topics/endangered-elements.html Periodic table of endangered elements]
* [http://www.periodictable.com/ Periodic table of samples]
* [http://www.periodicvideos.com Periodic table of videos]
* [http://www.webelements.com WebElements]
 
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[[Category:Chemical elements| ]]
[[Category:1869 works]]
[[Category:Dmitri Mendeleev]]
[[Category:Russian inventions]]
 
 
 
 
 
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