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100
Democritus
Proposed first idea of the atom: substances made up of tiny indestructible, indivisible particles called "atomos." -
100
Aristotle
He felt that regardless of the number of times you cut a form of matter in half, you would always have a smaller piece of that matter. -
100
Alchemists
Laid down the foundation of the modern day Periodic Table of the elements. -
LaVoisier
Law of Conservation of Mass: matter cannot be created or destroyed, only rearranged. -
John Dalton
Law of Multiple Porportions: same two elements can combine in different compounds: ratio of first element is fixed, while the second element varies. Proposed the first Atomic Theory. -
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. -
W.K. Roentgen
Discovered x-rays. -
Henri Becquenerel
Discovered that uranium ores emit radiation resembling x-rays and that it exposed film. -
The Curies
Studied uranium and thorium and called their spontaneous decay process "radioactivity". They discovered the radioactive elements polonium and radium. -
Max Planck
Quantium Theory: energy is not emmited constantly, but in small packets called quantum. -
Hans Geiger
Developed an electrical device to "click" when hit with alpha particles. -
Robert Millikan
Performed oil drop experimant, which determined the charge of electrons as negative. -
Ernest Rutherford
Studied substances, especially alpha particles. Conducted gold foil experiment: he bombarded gold foil with alpha particles. Most particles passed through the foil but some were deflected. He concluded that the atom is mostlhy empty space, with a very small positive nucleus core. -
Neils Bohr
Improved upon the atomic model by trying to answer the question: why aren't electrons pulled into the nucleus? -
Erwin Schrodinger
Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. -
James Chadwick
Discovered the neutron. -
Lise Meitner
Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction. -
Glenn T. Seaborg
Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.
