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Lecture 1.2 – Development of Atomic Theory

Lecture 1.2 – Development of Atomic Theory. What was Dalton’s contribution to atomic theory?. I. Dalton ’ s Model of the Atom. Draw this!. What was Thomson’s contribution to atomic theory?. I. J . J. Thomson. First evidence for subatomic particles. Made discovery in 1896. +. -. +. -.

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Lecture 1.2 – Development of Atomic Theory

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  1. Lecture 1.2 – Development of Atomic Theory

  2. What was Dalton’s contribution to atomic theory?

  3. I. Dalton’s Model of the Atom Draw this!

  4. What was Thomson’s contribution to atomic theory?

  5. I. J. J. Thomson • First evidence for subatomic particles. • Made discovery in 1896.

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  7. II. J. J. Thomson’s Experiment • Cathode-ray tube

  8. II. J.J. Thomson’s Experiment • Put a battery to the cathode tube and saw a beam form. • The beam contained subatomic particles. • Positive magnet next to beam = bent towards magnet. • Negative magnet next to beam = bent away from magnet.

  9. Table Work – What subatomic particle did he discover?

  10. III. Thomson’s Discovery • Thomson discovered the electron! • He discovered that atoms must contain some negatively charged particlescalled electrons. • Tells us nothing about the location of the electron.

  11. IV. Plum Pudding Model • Thompson proposed that electrons were balls of negative charge floating in a sea of positive charges. Draw this!

  12. What was Rutherford’s contribution to atomic theory?

  13. I. Ernest Rutherford • Disproved Plum Pudding Model with Gold Foil Experiment • Used alpha particles, which are small, positively charged particles.

  14. II. Rutherford’s Experiment • Shot positively charged alpha particles at gold foil • Most particles went through foil. • Small amount of the particles were deflected • Smaller amount were bounced back

  15. Rutherford noted: “It was almost as if you fired a 15-inch shell into a piece of tissue paper and it came back and hit you.”

  16. III. What Rutherford’s Data Meant • Most alpha particles went straight through = atom is mostly empty space. • Some alpha particles deflected = they came close to other electrons. • Small amount bounced back = hitting a very small, but very dense positively charged nucleus.

  17. IV. Important Point #1 • The atom is mostly empty space.

  18. V. Important Point #2 • The atom has very small, but very densenucleus. • Alpha particles that bounced back were coming into contact with nucleus.

  19. Draw this!

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