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Start of Atomic Theory TimelineDemocritus' atomic theory stated that all matter is made up of small indestructible
units he called atomsAristotle does not believe in atomic theory, rather he believes everything is made up of the four elements320 B.C.450 B.C.Isaac Newton theorized a world with solid masses in motion1704Antoine Lavosier created the Law of Conservation of Mass1743Joseph Priestly discovered Oxygen1774Joseph Proust creates the law of Definite Proportions1794Joseph Prous proposed the Law of Constant Composition1799Dalton Proposed that elements consisted of atoms that were identical and had the same mass1803Joseph Gay-Lussac announced the Law of Combining VolumesDalton went on to say that matter is made up of atoms and cannot be divided into smaller pieces and they cannot be destroyedMichael Faraday developed the two laws of electrochemistryWilhelm Roentgen observed chemicals that glow meaning that some rays were not deflectedHantaro Nagaoka claimed that an atom has a nucleusDmitri Ivanovich Mendeleev creates the first periodic tableThe Crookes demonstrate that cathode rays travel in straight linesJames Clerk Maxwell proposed the theory of electromagnetismG.J. Stoney theorized that electricity was comprised of negative particles known as electronsSir WIlliam Crookes discovers that cathode rays can be deflected by electric fields meaning they have a negative charge (electrons)E. Goldstein discovers canal rays which have a positive charge equal to an electronWilhelm Roentgen discovered X-raysHenri Becquerel discovered radiation by studying effects that X-rays have on photographic filmJ.J. Thomson determined the charge to mass ratio of electronsThe Curies discovered radium and polonium when they started to investigate radioactive substancesRutherford discovered alpha, beta, and gamma rays in radiationMarie Sklodowska Curie coined the term radioactivity after studying the decay process of uranium and thoriumFrederick Soddy came up with the term "isotope" to explain the unintentional breakdown of radioactive elementsMax Planck experimented with black body(an object that absorbs electromagnetic radium) which led to his Planck Postulate which describes the stability of electronsHantaro Nagoaka proposed an atomic model called the Saturnian Model to describe the structure of an atomRichard Abegg found that inert gases have a stable electron configurationJ.J. Thomson created the "plum pudding" model of an atom1904Albert Einstein was capable of proving the existence of atoms and was capable of counting themHans Geiger invented a device that could detect alpha particlesRobert Milikan proves that electrons have the same charge and massJ.J. Thomson discovered isotopes of stable elementsFrederick Soddy proposes the concept of isotopes, that elements with the same chemical properties may have different atomic weightGilbert N. Lewis publishes "The Atom and the Molecule" which is the foundation of Valance Bond TheoryH.G.J. Moseley discovered that the number of protons in an element determines its atomic numberFrancis William Aston used a mass spectrograph to identify 212 isotopesOtto Stern and Walther Gerlach establish concept of quantum mechanical spin in subatomic particlesNiels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.Louis de Broglie proposed that electrons have a wave/particle dualityWolfgang Pauli develops the exclusion principle, which states that no two electrons around a single nucleus may have the same quantum state, as described by four quantum numbers.Erwin Schrodinger combined the equations for the behavior of waves with the de Broglie equation to generate a mathematical model for the distribution of electrons in an atom.Cockcroft / Walton created the first nuclear reaction, producing alpha particlesPaul Dirac proposed the existence of antiparticles.James Chadwick discovered neutrons, particles whose mass was close to that of a proton.Lise Meitner, Hahn, Strassman discovered nuclear fission.Murrey Gal-Mann proposed the ideas of quarks(a part of an atom)Glenn Seaborg discovered eight transuranium elements.195119451938193219301929192619251923192219211919191619141913191019061905190319011900189918981897189518961886187918741873187018691861184518321808End of Events
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