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Atomic Theory Timeline

Atomic Theory Timeline. Compiled by Mrs. Johannesson in San Antonio ISD. Democritus (400 B.C.). proposed that matter was composed of tiny indivisible particles called atomos not scientifically tested "Nothing exists but atoms and empty space; everything else is opinion.".

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Atomic Theory Timeline

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  1. Atomic Theory Timeline Compiled by Mrs. Johannesson in San Antonio ISD

  2. Democritus (400 B.C.) • proposed that matter was composed of tiny indivisible particles called atomos • not scientifically tested • "Nothing exists but atoms and empty space; everything else is opinion."

  3. Democritus (400 B.C.) • rejected by Aristotle and others who believed that matter could be endlessly divided

  4. Alchemy (next 2000 years)

  5. Alchemy (next 2000 years) • “Cast to him the body of the King, and when he has devoured it…in a great fire…the King will be liberated” • antimony is alloyed with gold and heated in order to purify the gold • “…fierce gray wolf…subject to the sway of warlike Mars…” • antimony is found mixed with iron • “…offspring of the ancient Saturn…” • antimony is derived from lead

  6. John Dalton (1807) British Schoolteacher • based his theory on others’ experimental data Billiard Ball Model • atom is a uniform, solid sphere

  7. John Dalton Dalton’s Four Postulates 1. Elements are composed of small indivisible particles called atoms. 2. Atoms of the same element are identical. Atoms of different elements are different. 3. Atoms of different elements combine together in simple proportions to create a compound. 4. In a chemical reaction, atoms are rearranged, but not changed.

  8. Erwin Schrödinger (1926) Quantum mechanics • electrons can only exist in specified energy states Electron cloud model • orbital: region around the nucleus where e- are likely to be found

  9. Erwin Schrödinger (1926) Electron Cloud Model (orbital) dots represent probability of finding an e-

  10. James Chadwick (1932) Discovered neutrons • neutral particles in the nucleus of an atom Joliot-Curie Experiment • based his theory on their experimental evidence

  11. Alpha Particles Gamma rays? 5 MeV 50 MeV James Chadwick (1932) Joliot-Curie Experiment Be Energy values weren’t consistent.

  12. Alpha Particles Neutrons 5 MeV 5 MeV James Chadwick (1932) Chadwick’s Explanation Be • Energy values were consistent. • Also accounted for extra mass in the nucleus.

  13. James Chadwick (1932) Neutron Model

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