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The Periodic Table
Of Elements
Elements!
http://www.privatehand.com/flash/elements.html
Dmitri Mendeleev
Russian chemist Wrote own textbook
in 1868-1870 Organized elements,
noting their 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
Mendeleev's Predictions
Mendeleev predicted the properties and existance of elements missing from the 'gaps'
Mendeleev's Predictions
Mendeleev predicted the properties and existance of elements missing from the 'gaps'
The discovery of gallium in 1875, of scandium in 1879, and of germanium in 1886 supported the idea underlying Mendeleev's table (and matched his predicted properties well)
Problems
Some elements did not line up correctly when the atomic mass was used
Problems
Some elements did not line up correctly when the atomic mass was used
Reason for periodicity not understood in late 1800s
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 re-organization 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
Modern Periodic Table