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Discovery of Subatomic Particles

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He used a cathode ray tube to show that there was something inside an atom that ... charged central core called a nucleus- since some beams bounced right back. ... – PowerPoint PPT presentation

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Title: Discovery of Subatomic Particles


1
Discovery of Subatomic Particles
  • Fall 2007

2
I. Electrons
  • Discovered by J.J. Thompson in 1897
  • He used a cathode ray tube to show that there was
    something inside an atom that was negatively
    charged.

3
Experiment
  • Rays traveled from the cathode, which is
    positive, to the anode, which is negative.
  • He found that rays bent away form the negative
    charge and toward the positive charge.

4
Conclusion
  • The cathode ray was made up of an invisible
    negatively charged particle
  • Atoms must be composed of smaller particles
    called subatomic particles.

5
However
  • Experiments showed that the mass of an electron
    was 1/1840th that of a hydrogen atom
  • Where was all mass?

6
Proton Movie
  • The positively charged inside the nucleus of the
    atom
  • The nucleus was discovered by Rutherford in 1909
    using the Gold-foil experiment

7
Experiment
  • Set up a lead shield box containing Polonium
  • Radioactive Polonium emitted a beam called Alpha
    particles.
  • A sheet of gold foil was positioned in the way of
    the beam. The gold foil was surrounded by with
    Zinc Sulfide, which glows when struck with a
    positively charged part.

8
Found
  • Most particles passed right through as if it were
    not there at all.
  • A few beams were deflected. Some of the beams
    were deflected straight back!!!!!!!!

9
Concluded
  • Atoms are nearly all empty space- since most of
    the particles passed right through.
  • Atoms have a small dense positively charged
    central core called a nucleus- since some beams
    bounced right back.
  • All matter is made up of mostly empty space.
    What about a beam of steal??????????

10
Proton Movie
  • Protons make up about half of the mass of the
    atom
  • Each element has its own specific number of
    protons. Called atomic number
  • In a neutral atom the atomic number also tells us
    the number of electrons found in the atom.

11
Neutrons
  • Chadwick (1891-1974)
  • He built on Rutherfords work and discovered
    The Neutron
  • He deduced that Neutrons must not have a
    charge.
  • Neutrons

12
Neutrons cont
  • Neutrons are also found inside the nucleus.
  • Have the other half of the mass found in the atom
  • Neutrons Protons Atomic Mass

13
Isotopes
  • An isotope is an atom of an element that has the
    same number of protons but a different number of
    neutrons.
  • Its mass number is different from the one
    normally found for each element
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