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450
1st Proposal Everything is Made of Atoms
Year: 450 BC
Who: Greek philosopher Democritus
What: He proposed that all matter is composed of tiny, invisible particles he called "atomos" -
1st Atomic Theory
Year: 1803
Who: English school teacher John Dalton
What: Atomic Theory of Matter
1. Each element is composed of tiny particles called atoms
2. All atoms of a given element are identical, but they differ from those of any other element.
3. Atoms are neither created nor destroyed in any chemical reaction.
4. A given compound always has the same relative numbers and kinds of atoms. -
Cathode Ray Experiment - Part 2
particles that came from the cathode. He named these particles electrons. -
J.J. Thomson's Atom Model
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Cathode Ray Experiment - Part 1
Year: 1896
Who: J.J. Thompson
What: He measured the degree to which both a magnetic field and an electric field deflected the ray in a cathode ray tube. He also changed the gases in the tube and what materials the electrodes were made of.
Discovered: Magentic and electric fields deflect the rays path in a mathmatically predictible way. Also discovered that neither changing gases nor using different electrodes affected results. He concluded that a cathode ray is made of negatively charged -
Gold Foil Experiment
Year: 1909
Who: Ernest Rutherford
What: Aimed a beam of high speed alpha particles at a really thin piece of gold foil. Almost all passed through the foil, but about the fraction of 1 in 8000 got deflected directly back.
Discovered: The nucleus. The positively charged nucleus and the positively charged particles deflected each other when they hit. The rest of the particles made it through because most of the atom is empty space. -
Ernest Rutherford's Atom Model
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Discovery of Neutrons
Year: 1932
Who: James Chadwick
What: Discovered neutrons. He hit beryllium with alpha particles and allowed the radiation formt he beryllium hit paraffin wax. Protons were shot out of the wax. He showed that hsi observations could be explained if the radiation consisited of neutral particles with a mass about equal to that of a proton. These particles were named neutrons.
