Of ElementsChemistry Chapter 5 Section 1

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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