1. What are important discoveries related to the structure of an atom?

2. Three sub-atomic particles: Atom – basic unit of matter Element –substance consisting of one type of atom Compound – substance consisting of two or more different atoms

3. Democritus The Laughing Philosopher - Matter composed of atoms (tiny indestructible units) - No experiments, Little evidence - Smooth (sweet) and sharp (sour) atoms

4. John Dalton 1808 Dalton's Atomic Theory 1) Matter is made of atoms which are indivisible and indestructible. 2) All atoms of an element are identical in mass and properties. 3) Compounds are formed by two or more different kinds of atoms coming together. 4) A chemical reaction is a rearrangement of atoms.

5. JJ Thomson 1897 Lots of positive space with negative clusters Cathode Ray Experiment Discovered electrons Plum Pudding Model Chocolate Chip Muffin

6. What is plum pudding?

7. Ernest Rutherford 1908 Atoms= mostly empty space Discovered nucleus that contained positively charged particles Gold Foil Experiment Particles were deflected Electrons circle nucleus

9. Robert Millikan 1909 Oil Drop Experiment Calculated mass and charge amount of electron Flea on a Elephant Neglible Zero Mass

10. Neils Bohr1913 Electrons move in orbitals (energy levels) around nucleus Like planets and the sun Each orbital holds a certain number of electrons

11. James Chadwick 1932 Discovered neutrons Neutral particle with mass close to proton

12. Current Model

13. Watch “Atomos, Atomos” Video Watch Rutherford's Gold Foil Experiment