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History of Elementary Particles. 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.
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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
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.
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
Law of Conservation of Mass • Matter is not created or destroyed in a chemical reaction + =
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”
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.
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
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.
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
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
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)
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
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
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
Thompson (continued) • Now Thompson knew that there was a negative particle in the atom but where??? I’m tired…
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
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”
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
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
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”
Rutherford’s NEW Model of the Atom Rutherford hypothesized that the inside of an atom was a small mass called a nucleus. Yuck!
Rutherford’s Gold Foil Experiment Animation http://micro.magnet.fsu.edu/electromag/java/rutherford/index.html
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
Memory Helps • Rutherford • A Ford Truck carrying • Plum Pudding • Covered in Gold Foil • Discovered the Nucleus I’d “Rather” have a Ford (Rutherford)
3 Laws Always Whole #s One You Already Know… Law of Conservation of Matter Law of Definite Proportions Law of Multiple Proportions
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)
