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442 BCE
The Belief.
The Greek philosopher, Democritus began to believe that all matter is composed by indivisible elements. -
Theories.
Issac Newton theorized that there is an invisible microscopic mechanical universe with small, solid masses in motion. -
Proposal.
Scientist, John Dalton, proposed that elements contain atoms that are identicle and have the same mass. Compounds were atoms from different elements combined. -
Laws.
Michael Faraday developed the two laws of electrochemistry. -
Cathode-Ray Tubes.
J. Pucker built one of the first cathode-ray tubes. -
The Table.
Dmitiri Mendeleev created the first design of the Periodic Table. -
Theories.
G.J. Stoney theorized that electricity was comprised of negative particles, which he called Atoms. -
Experiments.
Sir William Crookes' experiements with the cathode-rays tubes which led him to comfirm the work of eariler scientists by demonstrating that cathode-rays have a negative charge. -
Canal Rays.
E. Goldstein discovered canal rays, which have a positive charge equal to an electron. -
X-Rays.
Wilhelm Roentgen discovered x-rays. -
Radiation.
Henri Becquerel discovered radiation by studying the effects of x-rays on photographic film. -
Electrons.
J.J. Thomson determined the charge to mass ratio of ratios. -
Radiation.
Rutherford discovered alpha, beta and gamma rays in radiation. -
Radium and Polonium.
Marie Sklodowska Curie discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium. -
Quantiziation.
Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light. -
Isotope.
Fredrick Soddy came up with the term "isotope" to explain the unintentional breakdown of radioactive elements. -
Saturnian Model.
Hantaro Nagaoka proposed atomic model called the Saturnian Model to describe the structure of an atom. -
Stable Electron Configuration.
Richard Abegg found that inert gases have a 'stable electron configuration.' -
Alpha Particles.
Hans Geiger invented a device that could detect alpha particles. -
Atomic Number.
H.G.J. Moseley discovered that the number of protons in an element which determines its atomic number. -
Spectrograph.
Francis William Aston used a mass spectrograph to identify 212 isotopes. -
Atomic Structure Theory.
Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit. -
Particle Duality.
Louis de Broflie proposed that electrons have a wave/particle duality. -
Reactions.
Cockcroft / Walton created the first nuclear reaction, producing alpha particles. -
Anti-Particles.
Paul Dirac proposed the existence of anti-particles. -
Neutrons.
James Chadwick discovered neutrons, particles whose mass was close to that of a proton. -
Nuclear Fission.
Lise Meitner, Hahn, Strassman discovered nuclear fission. -
Period: to
Transuranium Elements
Glenn Seaborg discovered eight transuranium elements. -
Nuclear Reactor.
Enrico Fermi created the first man-made nuclear reactor.