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Democritus, greek philospher, discovers
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he proposed "atomic theory" with spherical solid atoms based on physical properites of mass,
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Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law
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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.
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Studied "canal rays" and found they were associated with the proton H+ he also used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 108
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Studied radiations emitted from uranium and thorium and named them alpha and beta.He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
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Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.