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Chapter 4

Chapter 4. Atoms. 4.1 Objectives. Identify who came up with the first theory of atoms? Discuss what Dalton added to the atomic theory? Explain how JJ Thomson discovered the electron? Describe Rutherford’s atomic model?. Key Terms. Electron Proton Neutron Nucleus.

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Chapter 4

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  1. Chapter 4 Atoms

  2. 4.1 Objectives • Identify who came up with the first theory of atoms? • Discuss what Dalton added to the atomic theory? • Explain how JJ Thomson discovered the electron? • Describe Rutherford’s atomic model?

  3. Key Terms • Electron • Proton • Neutron • Nucleus

  4. The Beginnings of Atomic Theory • Over 2000 years ago Greek philosopher, Democritus of Abdera • First stated that all matter was made of representative particles • He called these particles atomos- literally translated indivisible or unbreakable • Why was this such an educational risk? • He had no evidence to support his claim

  5. Alchemy…the birth of Chemistry • Since Democritus lacked evidence, many other theories were proposed • Chemistry did not become a science of measurement until the 1700’s • Between the time of Democritus and the 18th century alchemy reined • One main goal of alchemists was to turn inexpensive materials into gold! • Did they succeed?

  6. John Dalton • One century later, John Dalton, a school teacher, published his theory on atoms • He first suggested that atoms can join other atoms to form compounds • He also stated that all atoms of the same element are exactly alike (we will find out later that this is not exactly true)

  7. Dalton cont’d. • Dalton, unlike Democritus, used evidence to support his theory of atoms • Dalton conducted experiments and noticed that certain substances actually behave in predictable ways (Water reaction video) 2H2 + O2 2H2O • He also noticed that they happen in specific proportions.

  8. JJ (my man) Thompson • At the end of the 1800’s JJ Thompson conducted an experiment using a Crooke’s tube. • This is basically like the tube in old (not plasma, LCD, or projection) TV’s • The rays observed in these tubes were constructed of negatively charged parts of the atom. • This proved that atoms could be divided into smaller parts So…the word atom is a misnomer… a mis-no-WHAT!?

  9. More about my man…JJ • Thompson developed a model of the atom that was different from Dalton’s simple sphere. • Thompson’s model is referred to as the “plum pudding” model (I think plum pudding is something they ate in 19th century Britain) • I like to call it the chocolate chip cookie model

  10. The Plum Pudding Model

  11. Ernest Rutherford • Probably the most famous experiment ever conducted in science… • THE GOLD FOIL EXPERIMENT! • Ernest Rutherford used a radioactive source (we will talk more about this later) to shoot a thin piece of gold foil

  12. The Gold Foil Experiment

  13. Conclusions from the Gold Foil Experiment • Most of the atom is empty space • There is a massive, dense area at the center of the atom • The area at the center of the atom is small and positively charged • This positive massive region would become known as the nucleus

  14. Shortcomings of the GFE • It did not account for all the mass of the atom • Did not allow us to see that all atoms of the same element are not necessarily exactly alike

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