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Modern Physics: Introduction. Ch 27-1. Greeks first had atomic theory B.C. Smallest Unit of “what is” Atoms explained crystalline shapes Chemical Reactions always occurred in precise proportions. Atoms. Avogadro – Equal volumes of gas contain the same number of molecules

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atoms

Greeks first had atomic theory

    • B.C.
    • Smallest Unit of “what is”
  • Atoms explained crystalline shapes
  • Chemical Reactions always occurred in precise proportions
Atoms
enlightenment

Avogadro – Equal volumes of gas contain the same number of molecules

    • Late 1700s – Early 1800s
    • Mass varies according to the mass of the molecule
    • Avogadro’s Number – 6.022 x 1023
  • Periodic Table
    • Regular Spacing of Elements
Enlightenment
michael faraday

Early 1800s

  • Decomposed substances by passing

current through them.

    • Mass decomposed ∝ time and current
    • Mass transfer ∝ charge
    • Charge came only in set values
  • QUANTIZED!
Michael Faraday
size of the atom

By the 1880s a number of experiments established the approximate size of the atom

  • How big is a Copper Atom?
    • ρcu = 8.96g/cm3
    • Atomic mass of Cu = 63.6g/mol
    • NA = 6.022x1023 atoms/mol
  • ρ = m/V = mmol/Vmol =mmol/(NA * V1 atom Cu)
  • V1 atom Cu = mmol/(NA * ρ) = 1.18 x 10-29m3
  • If cube V = l*w*h , then 2.3 x 10-10m per side
  • If sphere V = (4/3)πr3 , then 1.4 x 10-10m radius
  • 10-10m = 1 Angstrom
Size of the Atom
x rays

1895 William Roentgen

    • Cathode Ray Tube
      • Rays passed through light objects
      • Exposed film (like light)
      • Photographs of the shadows of the bones of the hand
      • Like light, it was not deflected by electrostatic or magnetic fields (NO Charge)
      • Rays discharge electrified objects
X-Rays
x rays1

Roentgen believed X-Rays to be a wave

    • Diffraction – NO
    • Reflection – NO
    • Polarization – NO
  • Problem – d ~= λ for diffraction to be observed
  • λ = 0.1nm !!!!!
  • 1912 first partial diffraction
  • Roentgen was awarded the 1st Nobel Prize in Physics
X-Rays
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