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GSCI 163

GSCI 163. Lecture 2. Atomic theory. What are things made of? Imagine dividing an object into smaller and smaller units. Is there a limit to how much we can divide?. Atom. Means “ uncuttable ”. Democritus (460-362 BC). John Dalton (1766 – 1844). All matter is made of atoms

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GSCI 163

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  1. GSCI 163 Lecture 2

  2. Atomic theory • What are things made of? Imagine dividing an object into smaller and smaller units. Is there a limit to how much we can divide?

  3. Atom • Means “uncuttable”. Democritus (460-362 BC)

  4. John Dalton (1766 – 1844) • All matter is made of atoms • Atoms cannot be created or destroyed. • All atoms of a given element are identical in mass and properties. Different elements differ from each other because they are made of different atoms. • Compounds are formed by the combination of two or more kinds of atoms in precise ratios. • A chemical reaction is a rearrangement of atoms.

  5. Is the atom indivisible? • J.J. Thompson – discovery of the electron 1897. The cathode ray tube

  6. What is the electron? • Robert A. Millikan in 1906 measured the charge of a single electron

  7. The model of the atom at this point • Positive and negative charges mixed like raisin in jello

  8. Discovery of the nucleus • Ernest Rutherford in 1907 found that the atom has a nucleus made of positive particles. • 100,000 smaller than the orbit of the electron

  9. How is the nucleus held together? • We need a glue to overcome electrical repulsion! • New particle = neutron • James Chadwick in 1932

  10. Dmitri Mendeleev

  11. Next class Atomic states • Read handout day 3 • Quiz on these topics (first 10-15 min of class)

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