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400
Democritus
[No Date, Month, or Year.]
-400 B.C. Greek era.
-reffered to an "atom" as nature's basic paricle.
-based on the greek word, "invisible." -
John Dalton
[No Month or Date. Year Provided.]
-Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
Antoine Henri Becquerel
-was born in Paris on this date.
-1896, made a discovery in radioactivty atoms. -
William Crookes
[No Month or Date Given. Year Provided].
-Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. -
Niels Henrik David Bohr
-was born in Copenhagen on this date.
-discovered energy levels in 1913. -
James Chadwick
-was born in Cheshire, England on this date.
-1932, makes a discovery in the domain of nuclear science. provided the exsistence of neutrons. -
J.J. Thomson
-1897- Studied "canal rays" and found they were associated with the proton H+ . - Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 108 coulombs/gram. -
R.A. Millikan
[No Date, or Month.]
-1909,Oil drop experiment.
-determined the charge (e=1.602 x 10-19 coulomb) and the mass (m = 9.11 x 10-28 gram) of an electron. -
H.G.J Moseley
[No Date, or Month]
-1914,Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Ernest Rutherford
-1911,Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil. He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
