2. The Development of a Modern Theory of the Atom

3. Democratus (460-370 B.C) Matter is composed of small, indivisible particles called atomos. Aristotle Matter is continuous - there is no smallest piece Who was right?

4. John Dalton (published 1803-07) 1.Elements are composed of atoms 2. All atoms of a given element are identical; 3. Atoms of different elements are different 4. Atoms of an element are not changed by chemical reactions 5. Compounds are formed when atoms combine 6. Led to the law of conservation of mass 7. Law of multiple proportions:

5. Law of Conservation of Mass Matter is neither created or destroyed. How does this lead to the balancing of equations?

6. Law of Multiple Proportions When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.

7. Example : 4 Nitrogen and oxygen combine in several different ratios. Mass of Nitrogen that combines w/ 1g of oxygen compound a1.750 g compound b0.8750 g compound c 0.4375 g 1.750 = 2 ;.875 = 2 ; 1.750 = 4.8750 1.4375 1.4375 1

8. The Cathode Ray Tube corpuscles Partial vacuum

9. Thomson (published 1897) Charge to mass ratio for electrons 1.76 x 10 8 C/g

10. Thomson Model of the Atom Plum pudding model Positive dough Negative raisins or corpuscles

11. Millikan's Oil Drop Experiment Click in this box to enter notes. Copyright © Houghton Mifflin Company. All rights reserved.

12. Millikin’s Oil drop experiment (published 1909) charge of electron = 1.60 x 10 -19 C

13. Millikan’s Oil Drop Experiment (Published in 1909)

14. Combining Millikins and Thompsons work we get 1.6 x 10 -19 C 1.76 x 10 8 C/g = 9.11 x 10 -28 g The mass of one electron

15. Rutherford’s First experiment (1871-1937) electrons energy Helium nuclei 2 4 He

16. Gold Foil Experiment Click in this box to enter notes. Copyright © Houghton Mifflin Company. All rights reserved. Go to Slide Show View (press F5) to play the video or animation. (To exit, press Esc.) This media requires PowerPoint® 2000 (or newer) and the Macromedia Flash Player (7 or higher). [To delete this message, click inside the box, click the border of the box, and then press delete.]

17. Rutherford’s Gold Foil Experiment (1910) 

19. If the nucleus were blown up to the size of a tennis ball and placed on the fifty yard line of our football field where would the first electron be found? It would be a firefly cruising out past brown road. So what is an atom mostly? NOTHING! So what are you mostly? NOTHING!

20. What are the fundamental particles that make up an atom? Protons - positive charge of 1 and a mass of 1 amu Neutorns - no charge and a mass of 1 amu Electrons - negative charge of one and a mass of 1/1800 amu What are protons and neutrons made of? Quarks What are quarks made of? Strings What do you get when a string is unbound? So what are protons and neutrons mostly? NOTHING ! Energy E = mC 2

21. What would happen if two atoms were brought into proximity of each other?