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History of the Atom

History of the Atom. The Greeks (~2500yrs ago). Democritus a) 1 st idea of atom – smallest particle. Aristotle Observations, no experimentation All matter made up of 4 elements: Air, water, fire earth. 2. Antoine La Voisier 1743-1794. Discovered several elements.

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History of the Atom

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  1. History of the Atom

  2. The Greeks (~2500yrs ago) • Democritus a) 1st idea of atom – smallest particle • Aristotle • Observations, no experimentation • All matter made up of 4 elements: • Air, water, fire earth

  3. 2. Antoine La Voisier1743-1794 • Discovered several elements b) Worked with law of conservation of mass c) Considered the Father of Modern Chemistry d) Beheaded during French Revolution

  4. 3. John Dalton(1766 - 1844) • Atomic Theory 1. Atoms are indivisible 2. All atoms of same element are identical BUT different than atoms of same element 3. Atoms combine in simple whole # ratios 4. Chemical rxns occur when atoms combine, split or rearrange

  5. 4. Thomson, Sir J.J. (1856-1940) • Cathode ray tube experiment (aka… raison bun or plum pudding model) • Set up a glass tube, free of air with magnets on each side • Sent a stream of particles thru it and observed which way they were deflected • Credited with discovery of electrons

  6. 5. Ernest Rutherford1871-1937 a) Gold Foil Experiment • Set up screen with thin Au foil in front • Shot stream of alpha particles (42He) thru • Most particles went straight thru, few deflected • Since 42He is + charge, once deflected, it’s off of something else + • Credited with discovery of nucleus with + charge due to protons

  7. 6. James Chadwick Discovered neutron 1. Same mass & location as proton

  8. Neils Bohr 1885-1962 • Solar system model of the atom • Electrons orbit nucleus in orbits called ENERGY LEVELS • Quantum – bundle of energy that an e- needs to change level • When e- change levels – not stable, they fall back towards nucleus & release energy in form of light that we see as colors (ROY G BIV)

  9. 8. Schrödinger • Quantum Mechanical Model 1. Deals with probability of where the electron is most likely located… Near the nucleus

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