Of Elements Chemistry Chapter 5 Section 1 The

Of Elements Chemistry Chapter 5 Section 1 The Periodic Table

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Dmitri Mendeleev Russian chemist Wrote own textbook in 1868 -1870 Organized elements Noted properties repeated (periodicity) when organized by atomic mass

Dmitri Mendeleev Some 'gaps' seemed to exist in his table of approximately 60 elements Predicted new elements would be discovered to fill the gaps (1869)

Mendeleev's Predictions Mendeleev predicted the properties and existance of elements missing from the 'gaps' Support (matched the predicted properties well): The discovery of gallium (est. mass 68) in 1875 Discovery of scandium (est. mass 45) in 1879 Discovery of germanium (est. mass 70) in 1886

Periodic Law Success of Mendeleev periodic table supports periodic law The physical and chemical properties of elements reoccur in a systematic manner Julius Lothar Meyer also proposed this in 1870

Problems Some elements did not line up correctly when the atomic mass was used Mendeleev moved 17 elements to line up properties instead of mass Reason for periodicity not understood in late 1800 s

Henry Gwyn Jeffreys Moseley Found relationship between X-ray wavelength and atomic number in 1913 (Moseley's Law) This allowed calculation of atomic number, and reorganization of elements

Henry Gwyn Jeffreys Moseley Predicted existance of technetium and promethium Furthered understanding of Rare Earth Elements (Lanthanide series) Periodic table reorganized by atomic number, and problem elements were resolved

Noble Gases Unknown when Mendeleev made table Argon discovered by Lord Rayleigh 1895 William Ramsey suggested argon grouped with helium in “zero group” 1898 By the turn of the century, helium, argon, neon, krypton and xenon had been discovered

Glenn Seaborg Discovered plutonium in 1940 Helped discover all transuranic elements from 94 to 102 Placed actinide series below lanthanide series on table Last major change to periodic table

Modern Periodic Table