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Chapter 4 (p. 87)

Chapter 4 (p. 87). Goal 2-Learner will build an understanding of the structure and properties of matter. 2.01-Analyze historical development of the current atomic theory: Democritus, Dalton, Thomson, Millikan, Rutherford, Chadwick, Bohr model and quantum mechanical model. The Indivisible Atom.

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Chapter 4 (p. 87)

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  1. Chapter 4 (p. 87) • Goal 2-Learner will build an understanding of the structure and properties of matter. • 2.01-Analyze historical development of the current atomic theory: Democritus, Dalton, Thomson, Millikan, Rutherford, Chadwick, Bohr model and quantum mechanical model.

  2. The Indivisible Atom The beginning

  3. History • Democritus • 2000+ years ago (400B.C.) • Came up with idea of the atom- means “indivisible” • Aristotle • (350 B.C.) didn’t believe in atoms • Came up with first 4 elements

  4. learn this! Dalton’s Atomic Theory All matter is made of atoms. Atoms of same elementhave the same size, mass, and properties. (Different atoms of a specific element are different from any other element.) Atoms can’t be subdivided, created or destroyed. Atoms of different elements combine in whole number ratios to make compounds. In chemical reactions, atoms can be combined, separated, and rearranged. go

  5. Some parts of Dalton’s theory were wrong: • atoms are divisible into smaller particles (subatomic particles) • atoms of the same element can have different masses (isotopes- atoms of the same type with different masses) • Most important parts of atomic theory: • all matter is made of atoms • atoms of different elements have different properties

  6. The Divisible Atom!

  7. Discovery of Electron • J.J. Thomson (1901) discovered electrons using CRT. • His model was called “Plum-pudding” • Concluded: particles were e- w/small mass What did it lack? Thomson working with CRT

  8. CRT

  9. Robert Milliken (1909) • Using the “Oil –Drop” experiment (next slide) Milliken determined the charge and mass of an e- (mass 1/1840 amu charge -). Actual apparatus used. go

  10. He applied a charge to falling drops of oil • Air was ionized (lost e-) • Oil captured these e- and became negative • He created an electric field which would suspend drops with charges (others fell thru) • Those suspended he calculated their mass with 2nd law: F= m x g

  11. Discovery of Nucleus • Ernest Rutherford (1911) discovered the nucleus by the famous Gold-foil experiment Alpha were He atoms go

  12. Ernest Rutherford-1911 • Experiment: “gold foil” • Aimed: + charges(alpha particles) at foil • Most: went through(which means?) • Some: repelled(why would they repel?) • Proved: dense center (nucleus) w/ p+ • “Pig face” model—draw on board go

  13. Niels Bohr-1913 • Discovered: rings • For: electrons • Rings also called: clouds, shells, levels, orbits

  14. James Chadwick is credited with discovering the neutron in 1932 • He used a method created by Irene Curie and her husband that detected particles given off by radioactive elements end

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