Atoms: Nuclear Interactions

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Atoms Nuclear Interactions

• Part One
• The Nature of Atoms
• Survey http//griffithchem.com/miscellaneous/Ch2
  02120nuclear20misc20papers.pdf

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Different Kinds of Radiation

• 1. Are all atoms always unchanging?
• No, Some atoms do change and become other types
  of atoms
• 2. What is radiation? What is radioactive decay?
• Energy and particles emitted when an atom breaks
  up. The process by which an atom breaks up is
  called Radioactivity.

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• 3. What is some of this energy in the form of?
• High Energy EM Radiation(Electromagnetic)

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EM Spectrum
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• 4. What are the properties of EM radiation ?
• 1. waves of energy with no mass
• 2. Travels at speed of light
• 3. Can travel through a vacuum unlike sound
• 4. Emitted by atoms when they decay or when they
  are energized (a light bulb)
• 5. Moves in bundles of energy called photons, at
  their own frequency
• 6. The higher the frequency, the higher the
  energy, the more dangerous

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• 5. How we are affected by nuclear radiation is
  dependent on what?
• The energy of the radiation
• 6. What is ionizing radiation?
• Highest energy therefore greatest potential for
  causing harm to us

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• 7. How can it cause you damage?
• Like ionization energy, it can knock away e- from
  an atom or molecule changing how it acts.
• 8. What part of EM radiation is ionizing?
• UV, X-rays, Gamma rays, Cosmic rays

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• 9. What is nonionizing radiation? Give some
  examples
• Lower energy emissions, transfers energy to atoms
  but not enough to knock electrons away. Large
  exposures to these can also kill you!
• (Microwave, Radiowaves, Infrared)

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• 10. What is a good analogy to distinguish between
  being hit by nonionizing radiation and ionizing
  radiation?
• Being hit by a speeding baseball (non-ionizing)
  and a speeding bullet (ionizing). Impact in
  Baseball is more spread out so body can absorb
  the energy with less damage.
• 11. React to this All radiation is harmful and
  should be avoided.

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II. The Great Discovery

• 12. Who was studying fluorescence and when?
• German physicist W.K. Roentgen, he studied
  minerals that glowed when hit by a beam of
  electrons.
• 13. What are beams of e- called?
• cathode rays
• Electron streams always flow toward the positive
  side, in a battery or a light bulb called the
  cathode.

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Roentgens wife-first x-ray
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WK Roentgen
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• 14. What are cathode ray tubes used for today?
• TV and Monitor Images
• 15. How did Roentgen discover X-rays?
• Was working with a CRT covered with black paper
  when he saw a fluorescent material glowing across
  the room. Theorized that the CRT was also
  emitting a type of radiation that could pass
  through black paper.

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Early Cathode Ray Tube
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First X ray Machine
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X-rays technology!
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Later X ray Tube
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• 16. How far x-rays will penetrate depends on
  what?
• Depends on the thickness and identity of the
  material.
• 17. Give some characteristics of x-rays
• Cannot pass through dense materials such as lead
  and bone. They are high energy EM radiation.

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Henri Becquerel
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• 18. What part did the Frenchman Henri Becquerel
  play in the story of x-rays?
• He discovered that certain minerals gave off
  X-rays.
• 19. Further research into x-rays led to what?
• That some of the rays being given off by such
  minerals as Uranium contained too much energy to
  be X-rays, Radiation was then discovered by
  Pierre and Marie Curie!

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Becquerels experiment
Radioactive material sat in a window sill, then
on a photographic film. However, when placed in a
drawer, it still exposed the filmwe later
figured out that radioactivity gave off the rays
that exposed the film.
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• Do Chemquandary 1 on page 415

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• 20. Who were the early pioneers of radioactivity?
  What ore did they get their Uranium from?
• Pierre and Marie Curie-Pitchblende
• 21. What other 2 radioactive elements did they
  discover?
• Polonium and Radium

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Marie Curie
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Marie Curie
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Pierre Curie
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III. Nuclear Radiation

• 22. What scientist was responsible for the
  discovery of two parts of the atom? What type of
  rays did he work with?
• Ernest Rutherford
• Alpha and beta rays

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• 23. What other type of ray was discovered but was
  at first thought to be unrelated to the atom
  structure?
• Gamma rays
• Important we now know the 3 types of nuclear
  radiation
• Alpha particles (positive)
• Beta particles (negative
• Gamma rays (neutral)

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Scientists knew that in a magnetic force
positives deflected one way, negative things
another way, and neutral things would not be
deflected so they figured out what these nuclear
radiation types were like.
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III. The Gold Foil Experiment

• 24. What was the most popular model of the atom
  before Ernest Rutherford?
• Atom was a solid mass of positively charged
  materials (not sure what they were) with
  negatively charged electrons imbedded within,
  like raisins in a pudding called Plum Pudding
  model and was proposed by J. J. Thomson.

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JJ. Thomson
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JJ Thomson and his CRT
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Thomson Model
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• only matter can be bent like that, it is called
  inertia. The bending of the indicated that the
  stream was made of particles

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• Thomson introduced his model in 1904
• a sphere of positive charge with e- embedded in
  it
• called Plum Pudding Model

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• In 1908, the proton was discovered by the New
  Zealand scientist, Ernest Rutherford in his
  famous Gold Foil Experiment

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History of Atomic Theory

• Rutherford with his assistant W.H. Geiger

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History of Atomic Theory
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• Rutherford theorized that if the Plum Pudding
  model was correct. The number of positive and
  negative particles in an atom would be the same
  with the particles evenly spread within the atom

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• the result was completely unexpected by
  Rutherford and his assistant Geiger(who actually
  performed the experiment)
• Rutherford was forced to rethink the model
  realizing that the only explanation was that all
  the positive particles must have been together in
  a nucleus

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Ernest Rutherford(1871-1937)

• New Zealander who went to study in Cambridge
• was really interested in studying radio waves but
  was convinced to study radioactivity by his
  professor
• discovered and explained alpha and beta particles

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• noticed that the radioactive element called
  Thorium gave off Argon gas thus proving that
  transmutation could occur
• was influenced by Marie Curies work
• guided and influenced 10 future Nobel prize
  winners

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Rutherford
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Rutherford
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• 25. Describe the gold foil experiment
• Beam of Alpha particles (positive) was focused on
  a sheet of Gold foil about 3000 atoms thick. A
  specially coated screen that emitted a flash of
  light when an alpha particle landed on it
  surrounded the sheet. Rutherford expected the
  alphas to pass right through it because there
  would be nothing big enough or positive enough in
  the atom to deflect it. BUT, 1 in every 20,000
  was deflected!

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• 26. Describe the model that was developed due to
  this experiment
• Whatever the positive alphas must have hit must
  have been vary large and very positive. The
  Rutherford model was proposed-the atom had a
  positive nucleus with negative electrons orbiting
  around it like planets around the sun

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Rutherford Model
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Architecture of Atoms

• 27. List the ways that the atomic model has
  changed since the turn of the century
• 1. E- are not really orbiting, we think they
  move around in a specific area called orbitals,
  you can never know the exact location of the e-

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• 2. Nucleus itself is composed of two different
  types
• of particles-Protons() and Neutrons(no charge),
  they are much larger than e-. Most of the atoms
  mass is taken up by the and n
• 3. Nucleus takes up 1/10 the diameter of the
  atom-the rest is the electron cloud

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• 28. What are isotopes? Give some examples
• atoms of the same element with the same number of
  protons but different number of neutrons
• C-14(6, 8 n) C-12(6, 6n)
• F-19(9, 10n) F-20(9, 11n)

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29. What is a radioisotope? if an isotope has an
unstable nucleus and tends to decay, meaning it
is radioactive
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• 30. What are atomic numbers?
• The number of protons in an atom
• 31. Where can you find the atomic number on the
  periodic table?
• It is the big whole number above the symbol
• 32. What is the symbol for atomic number?
• Z

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• 33. What are mass numbers?
• the sum of the protons and neutrons
• 34. Where can you find the mass number on the
  Periodic Table?
• Below the symbol(round up or round down)

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• 35. What is the symbol for the mass number?
• A

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• 36. What is a nuclear symbol?
• Tells you the mass number and atomic number of an
  isotope
• A Z X
• C-14 146C
• Do Building Skills 1 on page 421

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Isotopes in Nature

• 37. How many elements have isotopes?
• Most
• 38. How does this present a problem to the
  periodic table?
• The Periodic Table gives the relative mass of the
  elements. It takes into consideration 2 things
• a. How abundant each isotope is
• b. The mass of each isotope

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• 39. What did Marie Curie originally think about
  isotopes?
• She thought that radioactivity was a
  characteristic of only heavy elements
• (all elements above 83(Bi) are radioactive.) but
  so are some of the smaller elements

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Do Building Skills 2 on page 423
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Scientists knew that in a magnetic force
positives deflected one way, negative things
another way, and neutral things would not be
deflected so they figured out what these nuclear
radiation types were like.
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Do Making Decisions on page 425
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Working with Radiation