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)