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History of Elementary Particles. Greeks invented concept of Atom approximately 2500 years ago Later thought matter was made up of fire,water,air,earth.

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Presentation on theme: "History of Elementary Particles. Greeks invented concept of Atom approximately 2500 years ago Later thought matter was made up of fire,water,air,earth."— Presentation transcript:

1 History of Elementary Particles

2 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 Let’s call it … an atom.

3 400 B.C A.D A.D. Columbus Discovers the West Greeks invent concept of atom 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:  H 2 O - 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.

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

11 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 Atomic 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)

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

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

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

18 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 Yum Yum! Rutherford hypothesized that the inside of an atom was a mass with bits of matter mixed in. 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 Yuck! Rutherford hypothesized that the inside of an atom was a small mass called a nucleus.

23 Rutherford’s Gold Foil Experiment Animation d/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 One You Already Know… Always Whole #s 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)


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