Of ElementsChemistry Chapter 5 Section 1
http://www.privatehand.com/flash/elements.html
Russian chemist Wrote own textbook
in 1868-1870 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