Development of the Periodic Table

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  • Dobereiners Law of Traids 1780-1849

    German chemist Johann Dobereiner odered the elements based on similarities (atomic weight).

  • 60 elements By the 1860s

    By 1860 about 60 elements were known and a method was needed for organization. In fact many scientists made significant contributions that eventually enabled Mendeleev to construct his table. The periodic table did not end with Mendeleev but continued to take shape for the next 75 years.

  • 1820-1886 Aleandre Beguyer de Chancoutios

    It was a 19th century geologist who first recognized periodicity in the physical properties of the elements. Alexandre Beguyer de Chancourtois (1820-1886), professor of geology at the School of Mines in Paris, published in 1862 a list of all the known elements

  • Lord Rayleigh and William Ramsey

    Lord Rayleigh (1842-1919) and William Ramsey (1852-1916) greatly enhanced the periodic table by discovering the "inert gases." In 1895 Rayleigh reported the discovery of a new gaseous element named argon. This element was chemically inert and did not fit any of the known periodic groups. Ramsey followed by discovering the remainder of the inert gases and positioning them in the periodic table

  • 1834-1907 Dimitri Mendeleev

    Then in 1869, Russian chemist Dimitri Mendeleev (1834-1907) proposed arranging elements by atomic weights and properties (Lothar Meyer independently reached similar conclusion but published results after Mendeleev). Mendeleev's periodic table of 1869 contained 17 columns with two partial periods of seven elements each (Li-F & Na-Cl) followed by two nearly complete periods (K-Br & Rb-I).

  • Moseley's Periodic Law

    Soon after Rutherford's landmark experiment of discovering the proton in 1911, Henry Moseley (1887-1915) subjected known elements to x-rays. He was able to derive the relationship between x-ray frequency and number of protons. When Moseley arranged the elements according to increasing atomic numbers and not atomic masses, some of the inconsistencies associated with Mendeleev's table were eliminated. The modern periodic table is based on Moseley's Periodic Law (atomic numbers).

  • Modern Periodic Table

    The last major change to the periodic table resulted from Glenn Seaborg's work in the middle of the 20th century. Starting with plutonium in 1940, Seaborg discovered transuranium elements 94 to 102 and reconfigured the periodic table by placing the lanthanide/actinide series at the bottom of the table. In 1951 Seaborg was awarded the Nobel Prize in chemistry and element 106 was later named seaborgium (Sg) in his honor.