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Solid Masses in Motion
Isaac Newton proposed a mechanical universe with small solid masses in motion.
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Indestructible and Unchangeable
Atoms are indestructible and unchangeable. Atoms of an element cannot be created, destroyed, divided into smaller pieces, or transformed into atoms of another element. Dalton based this hypothesis on the law of conservation of mass as stated by Antoine Lavoisier and others around 1785.
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Atomic Theory
John Dalton proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
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7 Groups of Elements
Dmitri Mendeleev 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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Cathode
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.
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electron
British physicist J.J. Thomson discovered the electron
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Electricity
G.J. Stoney proposed that electricity was made of discrete negative particles he called electrons
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Alpha and Beta
Rutherford studied radiations emitted from uranium and thorium and named them alpha and beta. More Info -
Isotope Discovery
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Atomic Structure - Elements
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.
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Electron waves are similar to light waves
de Broglie Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein.
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Neutron Discovery
James Chadwick using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.
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New Periodic Table
Glenn Seaborg synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.
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Energy from Nucleus
Enrico Fermi conducted the first controlled chain reaction releasing energy from the atoms nucleus.
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