History of Elementary Particles: Atom Discovery Timeline and Experiments

1. History of Elementary Particles

2. Let’s call it … an atom. • Greeks invented concept of Atom approximately 2500 years ago • Later thought matter was made up of fire,water,air,earth Definition of Atom: Smallest particle of an element that retains the chemical identity of the element

3. Discovery Timeline 400 B.C 1700 A.D. 1492 A.D. 0 Greeks invent concept of atom Columbus Discovers the West About late 1700s some new ideas through experiments came to be discussed.

4. What Were Some of the Results of These Experiments? • Law of Conservation of Mass • Law of Constant Composition (also called Law of Definite Proportions) • Law of Multiple Proportions

5. Law of Conservation of Mass • Matter is not created or destroyed in a chemical reaction + =

6. Law of Constant Composition or Law of Definite Proportions • A chemical has exactly the same proportions no matter the size • Example: • Doesn’t matter if 3 crystals or a jar of salt • 66 % of mass is always Chloride • 33 % of the mass is always Sodium OR Same “Proportions”, Same “Composition”

7. Example of the Law or Constant Composition (Law of Definite Proportions) • What would happen if I take a small bite of cake or a GIANT bite of cake? • Would it taste the same? • The “Composition” of the cake is the same all the way through. • A COMPOUND (like sugar or salt) is the SAME no matter where you find it, or how much you have.

8. The Law of Multiple Proportions • Chemicals always combine in ratios of small whole numbers • Example: • H2O - Water • There will always be a 2 to 1 ratio between Hydrogen and Oxygen • Whether you have one water molecule or an ocean full water

9. Law of Multiple Proportions Example • Molecules are not made up of “1/2” or an atom or pieces of an atom • This proportion might be 1: 3/4 • Remember WHOLE numbers.

10. Discovery Timeline Late 1700s 400 B.C 1492 A.D. 1803 0 Greeks invent concept of atom Columbus Discovers the West New Experiments and Laws John Dalton and the Atomic Theory of Matter

11. Jeopardy Slide - Dalton • At age 12 Dalton was teaching the local school • Was reading Newton’s Book in Latin • Color Blindness was called “Daltonism” for a lengthy time

12. John Dalton - 1803Atomic Theory of Matter • UNIQUE - Atoms are unique from other elements • GROUPS - Compounds are combined in small whole numbers. • LAW OF CONSERVATION OF MATTER - atoms are rearranged or combined but not destroyed • INDIVIDUALS - Elements are composed of atoms (smallest building block)

13. Discovery Timeline Almost 1900 Late 1700s 400 B.C 1492 A.D. 1803 0 Greeks invent concept of atom John Dalton and the Atomic Theory of Matter Columbus Discovers the West New Exper-iments and Laws Thompson Discovers the Electron

14. John Thompson, circa 1900 Discovers Electron • Prior to this a man named Faraday hypothesized that atoms had a charge • Thompson hypothesized that the electrical charge was negative and that the particle had mass

15. Thompson’s Experiment using a Cathode Ray Tube (CRT) • Elements are neutral (no charge) • Thompson could alter path of particles by using magnets (that showed they had a charge) • The type of magnet showed that it had a negative charge battery magnets

16. Thompson (continued) • Now Thompson knew that there was a negative particle in the atom but where??? I’m tired…

17. Discovery Timeline Late 1700s 400 B.C 1492 A.D. Almost 1900 1803 1910 0 Greeks invent concept of atom Thomp-son Dis-covers the Electron John Dalton and the Atomic Theory of Matter Columbus Discovers the West New Exper-iments and Laws Rutherford discovers the nucleus

18. Jeopardy Slide Rutherford • Rutherford was not a brilliant man, often getting lost in Math, not terribly clever in experimentation, just tenacious and open-minded • His assistant was Hans Geiger, inventer of the “Geiger Counter”

19. Rutherford’s Model of the Atom Rutherford hypothesized that the inside of an atom was a mass with bits of matter mixed in. Yum Yum! He called the model the “Plum Pudding” Model

20. Rutherford’s Gold Foil Experiment • Rutherford set up very thin gold foil as a target • “shot” positive charges to foil • Watched patterns that positive particles made

21. Results of the Rutherford’s Experiment • Alpha particles (positive particles) went through • Only sometimes ‘bounced” back • Proved that nucleus was mostly empty space • Called center “nucleus”

22. Rutherford’s NEW Model of the Atom Rutherford hypothesized that the inside of an atom was a small mass called a nucleus. Yuck!

23. Rutherford’s Gold Foil Experiment Animation http://micro.magnet.fsu.edu/electromag/java/rutherford/index.html

24. What Do I Need to Remember ? • Greeks came up with Atom • 3 Laws that started it all… • Dalton - Atomic Theory of Matter • Thompson CRT Experiment • Rutherford’s Gold Foil Experiment

25. Memory Helps • Rutherford • A Ford Truck carrying • Plum Pudding • Covered in Gold Foil • Discovered the Nucleus I’d “Rather” have a Ford (Rutherford)

26. 3 Laws Always Whole #s One You Already Know… Law of Conservation of Matter Law of Definite Proportions Law of Multiple Proportions

27. Thompson Cathode Ray Tube

28. Daltons Theory of Matter • UGLI • U Unique (Elements are..) • G Groups (They are grouped in small whole number groups Law of Multiple Proportions) • L Law of Conservation of Matter • I Individual (Matter is made up of individual atoms)