Modern physics introduction
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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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Modern Physics: Introduction

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Modern physics introduction

Modern Physics: Introduction

Ch 27-1


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


Crystal diffraction

  • Space between atoms in a crystal is about 0.1nm

Crystal Diffraction


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