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58 mendeleevs table was his first published version

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[58] Mendeleev's table was his first published version; that of Meyer was an expanded version of his (Meyer's) table of 1864. [59] They both constructed their tables by listing the elements in rows or columns in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat. [60] The recognition and acceptance afforded Mendeleev's table came from two decisions he made. The first was to leave gaps in the table when it seemed that the corresponding element had not yet been discovered. [61] Mendeleev was not the first chemist to do so, but he was the first to be recognized as using the trends in his periodic table to predict the properties of those missing elements, such as gallium and germanium. [62] The second decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as tellurium and iodine, to better classify them into chemical families. With the development of theories of atomic structure, it became apparent that Mendeleev had unintentionally listed the elements in order of increasing atomic number or nuclear charge. [63] The significance of atomic numbers to the organization of the periodic table was not appreciated until the existence and properties of protons and neutrons became understood. Mendeleev's periodic tables used atomic weight instead of atomic number to organize the elements, information determinable to fair precision in his time. Atomic weight worked well enough in most cases to (as noted) give a presentation that was able to predict the properties of missing elements more accurately than any other method then known. Substitution of atomic numbers, once understood, gave a definitive, integer-based sequence for the elements, still used today even as new synthetic elements are being produced and studied. [64] Further development In 1871, Mendeleev published an updated form of periodic table (shown at left), as well as giving detailed predictions for the elements he had earlier noted were missing, but should exist. [65] These gaps were subsequently filled as chemists discovered additional naturally occurring elements. [66] It is often stated that the last naturally occurring element to be discovered was francium (referred to by Mendeleev as eka-caesium ) in 1939. [67] However, plutonium, produced synthetically in 1940, was identified in trace quantities as a naturally occurring primordial element in 1971, [68] and in 2011 it was found that all the elements up to californium can occur naturally as trace amounts in uranium ores by neutron capture and beta decay. [3]
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6/2/13 11:44 AM Periodic table - Wikipedia, the free encyclopedia Page 10 of 17 http://en.wikipedia.org/wiki/Periodic_table Short form of periodic table, as originally published by Mendeleev in 1871, updated with all elements discovered to 2012. Glenn T. Seaborg who, in
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58 Mendeleevs table was his first published version that of...

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