Editing Periodic table (section)

=== Early history ===
In 1817, German physicist [[Johann Wolfgang Döbereiner]] began to formulate one of the earliest attempts to classify the elements.<ref>{{cite journal|last1=Wurzer|first1=Ferdinand|title=Auszug eines Briefes vom Hofrath Wurzer, Prof. der Chemie zu Marburg|journal=Annalen der Physik|date=1817|volume=56|issue=7|pages=331–334|url=https://babel.hathitrust.org/cgi/pt?id=chi.096071138;view=1up;seq=351|trans-title=Excerpt of a letter from Court Advisor Wurzer, Professor of Chemistry at Marburg|language=de|doi=10.1002/andp.18170560709|bibcode=1817AnP....56..331.|access-date=15 August 2021|archive-date=8 October 2021|archive-url=https://web.archive.org/web/20211008024621/https://babel.hathitrust.org/cgi/pt?id=chi.096071138;view=1up;seq=351|url-status=live}} Here, Döbereiner found that strontium's properties were intermediate to those of calcium and barium.</ref> In 1829, he found that he could form some of the elements into groups of three, with the members of each group having related properties. He termed these groups [[Döbereiner's triads|triads]].<ref>{{cite journal|last1=Döbereiner|first1=J. W.|title=Versuch zu einer Gruppirung der elementaren Stoffe nach ihrer Analogie|journal=Annalen der Physik und Chemie|date=1829|volume=15|issue=2|pages=301–307|url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015065410634;view=1up;seq=315|series=2nd series|trans-title=An attempt to group elementary substances according to their analogies|language=de|bibcode=1829AnP....91..301D|doi=10.1002/andp.18290910217|access-date=15 August 2021|archive-date=8 October 2021|archive-url=https://web.archive.org/web/20211008024625/https://babel.hathitrust.org/cgi/pt?id=mdp.39015065410634;view=1up;seq=315|url-status=live}} For an English translation of this article, see: [https://web.lemoyne.edu/~giunta/dobereiner.html Johann Wolfgang Döbereiner: "An Attempt to Group Elementary Substances according to Their Analogies" (Lemoyne College (Syracuse, New York, USA))] {{Webarchive|url=https://web.archive.org/web/20190309161429/https://web.lemoyne.edu/~GIUNTA/dobereiner.html |date=9 March 2019 }}</ref><ref>{{cite book |last=Horvitz |first=L.|title=Eureka!: Scientific Breakthroughs That Changed The World |year=2002 |publisher=John Wiley |location=New York|isbn=978-0-471-23341-1 |oclc=50766822 |page=43|bibcode=2001esbt.book.....H}}</ref> Chlorine, bromine, and iodine formed a triad; as did calcium, strontium, and barium; lithium, sodium, and potassium; and sulfur, selenium, and tellurium. Today, all these triads form part of modern-day groups: the halogens, alkaline earth metals, alkali metals, and chalcogens.<ref>Scerri, p. 47</ref> Various chemists continued his work and were able to identify more and more relationships between small groups of elements. However, they could not build one scheme that encompassed them all.<ref>{{cite book|last=Ball|first=P.|author-link=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|page=100}}</ref>

[[File:Newlands periodiska system 1866.png|thumb|right|upright=1.5|Newlands's table of the elements in 1866.|alt=Newlands's table of the elements.]]
[[John Newlands (chemist)|John Newlands]] published a letter in the ''Chemical News'' in February 1863 on the periodicity among the chemical elements.<ref name=EB1911>{{cite EB1911 |wstitle=Newlands, John Alexander Reina |volume=19 |page=515}}</ref> In 1864 Newlands published an article in the ''Chemical News'' showing that if the elements are arranged in the order of their atomic weights, those having consecutive numbers frequently either belong to the same group or occupy similar positions in different groups, and he pointed out that each eighth element starting from a given one is in this arrangement a kind of repetition of the first, like the eighth note of an octave in music (The Law of Octaves).<ref name=EB1911/> However, Newlands's formulation only worked well for the main-group elements, and encountered serious problems with the others.<ref name=jensenlaw/>

German chemist [[Lothar Meyer]] noted the sequences of similar chemical and physical properties repeated at periodic intervals. According to him, if the atomic weights were plotted as ordinates (i.e. vertically) and the atomic volumes as abscissas (i.e. horizontally)—the curve obtained a series of maximums and minimums—the most [[electropositive]] elements would appear at the peaks of the curve in the order of their atomic weights. In 1864, a book of his was published; it contained an early version of the periodic table containing 28 elements, and classified elements into six families by their [[valence (chemistry)|valence]]—for the first time, elements had been grouped according to their valence. Works on organizing the elements by atomic weight had until then been stymied by inaccurate measurements of the atomic weights.<ref name="Meyer table">Meyer, Julius Lothar; Die modernen Theorien der Chemie (1864); [https://reader.digitale-sammlungen.de/de/fs1/object/goToPage/bsb10073411.html?pageNo=147 table on page 137] {{Webarchive|url=https://web.archive.org/web/20190102050414/https://reader.digitale-sammlungen.de/de/fs1/object/goToPage/bsb10073411.html?pageNo=147 |date=2 January 2019 }}</ref> In 1868, he revised his table, but this revision was published as a draft only after his death.<ref>Scerri, pp. 106–108</ref>