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Johann Dobereiner proposed the Law of Triads
The middle element in the triad had atomic weight that was average of the other two members. The other elements that contained evidence were Li Na K and Cl Br I. -
60 elements had been discovered.
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Alexandre Beguyer de Chancourtois published a list of all the known elements
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John Newlands wrote a paper proposing the Law of Octaves
Elements exhibit similar behaviour to the eighth element following it in the table. -
Dimitri Mendeleev proposed arranfing elements by atomic weights and properties.
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Mendeleev revised the 17-group table with eight columns (the eighth group consisted of transition elements)
This table exhibited similarities not only in small units such as the triads, but showed similarities in an entire network of vertical, horizontal, and diagonal relationships. The table contained gaps but Mendeleev predicted the discovery of new elements. -
Lord Rayleigh greatly enhanced the periodic table by discovering the "inert gases." He 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. -
Rutherford's landmark experiment of discovering the proton
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Henry Moseley 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. -
Glenn Seaborg discovered transuranium elements 94 to 102
He reconfigured the periodic table by placing the lanthanide/actinide series at the bottom of the table. In 1951 element 106 was named seaborgium (Sg) in his honor. -
The first inert gas compound was made in 1962
(xenon tetrafluoride) and numerous compounds have followed (see xenon compounds)--today the group is more appropriately called the noble gases.