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460
Democritus (Greece)
- Had proposed that all matter is made of infinite indivisible particles which differ from each other in form, position & arrangement http://scienceworld.wolfram.com/biography/Democritus.html
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Issac Newton (England)
- Proposed a mechanical universe with small solid masses in motion
- Also suggested that atoms were held together by attractions that we now call forces http://scienceworld.wolfram.com/biography/Newton.html
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John Dalton (England)
- First suggested the existance of an atom
- His original theories provided us with the weight of atoms which can distinguish one atom from another http://scienceworld.wolfram.com/biography/Dalton.html
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George Johnstone Stoney (Ireland)
- Calculated the electric charge of an atom
- Proposed that electricity was made of discrete negative particles called electrons http://atomictimeline.net/index.php
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Joseph John Thomson (England)
- Showed us the existance of subatomic particles through cathrode rays
- Research on rays led to a means of separating atoms & molecules according to their atomic weights http://scienceworld.wolfram.com/biography/Thomson.html
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Max Planck (Germany)
- Founder of the quantum theory
- Quantum theory has revolutionised our understanding of atomic & sub-atomic processes http://scienceworld.wolfram.com/biography/Planck.html
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Hantora Nagaoka (Japan)
- Created a “Saturnian” model (albeit slightly incorrect) of an atom with flat rings of electrons revolving around a positively charged atom http://atomictimeline.net/index.php
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Robert Andrews Milikan (America)
- Measured the charge of an electron using the oil drop experiment
- Allowed us to measure the charge to mass ratio of an electron http://atomictimeline.net/index.php http://en.wikipedia.org/wiki/Robert_Andrews_Milikan
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Ernest Rutherford (Britain/New Zealand)
- Established that the nucleus was very dense, small & positively charged
- Also assumed that the electrons were located outside the nucleus http://en.wikipedia.org/wiki/Ernest_Rutherford http://atomictimeline.net/index.php
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Henry Gwy-Jeffreys Moseley (England)
- Arranged the periodic table by their atomic numbers
- Used x-ray tubes to determine the charges in the nuclei of most atoms http://atomictimeline.net/index.php
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Niels Bohr (Denmark)
- Developed an explanation of atomic structure that underlies regularities of the periodic table of elements
- Expanded upon Rutherford’s theory by proposing that electrons travel only in successively larger orbits http://www2.lucidcafe.com/lucidcafe/library/95oct/nbohr.html
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James Chadwick (England)
- Used the alpha particles to discover a neutral atom particle with a mass close to a proton – thus discovered the neutron http://atomictimeline.net/index.php