Of Elements Chemistry Chapter 5 Section 1

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 Russian chemist  Wrote own textbook in  Organized elements  Noted properties repeated (periodicity) when organized by atomic mass

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

 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

 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

 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 1800s

 Found relationship between X-ray wavelength and atomic number in 1913 (Moseley's Law)  This allowed calculation of atomic number, and re- organization of elements

 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

 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

 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