1. Chapter 4 Sec. 1 Studying Atoms

2. Ancient Greek Atoms 2500 years ago, Democritus believe that all matter consisted of extremly small particles that couldn’t be divided Four Elements  Air, Water, Fire, Earth  Water = round and smooth  Earth = rough and prickley Greek Word atomos meaning “uncut”

3. Ancient Greek Atoms Aristotle believed that there wasn’t a limit to the number of times that an atom could be divided The model shown is Aristotle’s model to describe matter

4. Dalton’s Atomic Theory Reintroduces the study of atoms by 1800’s Evidence:  Mass of combined elements that combine when compounds form  Formed ratio’s

5. Dalton’s Atomic Theory Daltons Theory:  1) Elements composed of atoms  2) Atoms of same element are alike  3) Atoms of different elements differ  4) Compounds are formed by joining atoms of two or more different elements in the same way

6. Dalton’s Model John Dalton's atomic model was a simple sphere.

7. Thomson’s Model When objects rub, they gain ability to repel or attract Experiment used a glow beam in a tube with charged plates Beam was repelled by (-) and attracted by (+)

8. Thomson’s Model 1904 English physicist introduced the idea of negatively charged particles known as “electrons” He thought electrons were embedded into the atom Plum Pudding Model

9. Rutherford’s Atomic Theory Almost all mass of the atoms were concentrated in the center: called alpha particles  Asked student to conduct experiment (Marsden) Rutherford predicted particles to go straight through But……..

10. Gold Foil Experiment:  Shot a narrow beam of alpha particles at a gold foil  Alpha particles scattered instead  Reflecting off the positive nucleus

11. Nucleus B/c of gold foil experiment, brought up idea of a nucleus  Dense and positively charged