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Period: 624 BCE to 546 BCE
Thales of Miletus
Created the atomic theory that states that all matter is composed of particles called atoms. Date is unknown but he was alive between 624 BCE and 546 BCE.
[http://www.philosophers.co.uk/thales-of-miletus.html] -
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Democritus
Democritus states "by convention bitter, by convention sweet, but in reality atoms and void" Time is unknown and it is before 1704.
[http://atomictimeline.net/index.php] -
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Isaac Newton
Proposed a mechanical universe with small solid masses in motion. [http://atomictimeline.net/index.php] -
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John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. [http://atomictimeline.net/index.php] -
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Michael Faraday
Studied the effect of electricity on solutions. Invented the term "electrolysis" as a splitting of molecules with electricity and developed laws of electrolysis. Faraday himself was not a proponent of atomism. [http://atomictimeline.net/index.php] -
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J.Plucker
Built one of the first gas discharge tubes ("cathode ray tube"). [http://atomictimeline.net/index.php] -
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Dmitri Mendeleev
Arranged elements into 7 groups. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law. [http://atomictimeline.net/index.php] -
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Sir William Crookes
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. [http://atomictimeline.net/index.php] -
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E. Goldstein
Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron. [http://atomictimeline.net/index.php] -
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G.J. Stoney
Proposed that electricity was made of individual negative particles he called electrons. [http://atomictimeline.net/index.php] -
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J.J. Thomson
Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram and also studied "canal rays" and found they were associated with the proton H + . [http://atomictimeline.net/index.php] -
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Rutherford
Studied radiations emitted from uranium and thorium and named them alpha and beta. [http://atomictimeline.net/index.php] -
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Marie Sklodowska Curie
Studied uranium and thorium and called their spontaneous decay process "radioactivity". Marie and her husband Pierre also discovered the radioactive elements polonium and radium. [http://atomictimeline.net/index.php] -
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Max Planck
Used the idea of quanta (discrete units of energy) to explain hot glowing matter. [http://atomictimeline.net/index.php] -
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Fredrick Soddy
Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay. [http://atomictimeline.net/index.php] -
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Hantaro Nagaoka
Proposed a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. [http://atomictimeline.net/index.php] -
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Richard Abegg
Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity. [http://atomictimeline.net/index.php] -
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H.G.J. Moseley
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. [http://atomictimeline.net/index.php] -
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Francis William Ashton
Discovered the existence of isotopes through the use of a mass spectrograph. [http://atomictimeline.net/index.php] -
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Niels Bohr
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. [http://atomictimeline.net/index.php] -
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Louis de Broglie
Discovered that electrons had a dual nature-similar to both particles and waves(Particle/wave duality). [http://atomictimeline.net/index.php]