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Chapter Six Part I. Questions of the Day. What an atom? How are they made? What is spectroscopy? How is it used in Astronomy? How are atoms and spectroscopy related? Why is this important to astronomy?. Atoms. They emit and absorb energy Elements are unique atomic structures

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Questions of the day l.jpg
Questions of the Day

  • What an atom? How are they made?

  • What is spectroscopy? How is it used in Astronomy?

  • How are atoms and spectroscopy related? Why is this important to astronomy?


Atoms l.jpg
Atoms

  • They emit and absorb energy

  • Elements are unique atomic structures

  • Element A + Element B = Compound

  • Unit of a compound: Molecule



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Atomic Structure and Spectra

  • Electrons

    • J. J. Tomson (1897)

      • Cathode ray tubes

      • Negative versus Positive

      • Created electric field around the ray tube

      • Negative charged particles flowed away from positive terminal.


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Atomic Structure (cont.)

  • Electrons (cont.)

    • Robert Millikan (1906)

      • Charged oil drops were deflected using charged plates

      • Tomson had given limits to mass of electrons, but Millikan found the q/m

      • Masselectron = 9.11 x 10-11 kg

    • Tomson suggest raisin in plum pudding model

    • Another structure was suggested by presence of alpha, beta, and gamma particles


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Atomic Structure (cont.)

  • Nucleus

    • Ernst Rutherford (1907)

      • Focused a beam of alpha particles through a thin sheet of Au (Gold) then detected behind by zinc sulfide that sparked when alpha hit it.

      • Most particles went through the sheet of Au, but some were back scattered by a small object, assumed to be a nucleus

      • Regions assumed to be 10-13 to 10-8 cm


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Atomic Structure (cont.)

  • Nucleus (cont.)

    • Rutherford (1911)

      • Used alpha to break up the nucleus of a N (nitrogen) atom and found 7 discrete unit of charge like the electrons, but positively charged

      • Called the particles protons

      • Lead to atomic number for each element

    • Maxwell put the proton and electron together with the electron orbiting the proton


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Bohr Model of the Atom

  • Bohr’s theory

    • Allowed orbits have angular momentum conserved and angular force corrected

      • mvr = nh/2

      • kq1q2/r2 = mv2/r

    • Solving the equations simultaneously we get the Bohr radius of 0.529 X 10-10 m


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Bohr Model (cont.)

  • Stable orbits do not give off radiation, but the 21 cm line is an exception to this rule

  • Quantum jumps: used the H (hydrogen) atom

    • En = EI /n2

    • hf = EH – EI

  • Bohr model worked wonderfully for H, but did not work for higher elements so we needed a new science, Quantum Mechanics




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Quantum Mechanics

http://ahs.wcs.k12.va.us/Chem%20Web%20Final_files/image012.jpg


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Spectra and Elements

http://jersey.uoregon.edu/elements/Elements.html




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Electromagnetic Spectrum

http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/



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Gustav Kirchoff

  • 1824 –1887

  • Student of Gauss

  • Taught at Berlin, Brausla, and Hiedelberg

  • Vorleschugen uber Matematische Physik

  • Created laws for electrical circuits, spectroscopy, and topology in mathematics

http://www.hao.ucar.edu/public/education/sp/images/kirchhoff.jpg


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Kirchoff’s First Rule

  • A hot and opaque solid, liquid, or highly compressed gas emits a continuous spectrum.

  • Example: Light Bulb filament


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Kirchoff’s Second Rule

  • A hot, transparent gas produces a spectrum of bright lines (emission lines). The number of these lines depend on which elements are present in the gas.

  • Example: A neon sign


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Kirchoff’s Third Rule

  • If a continuous spectrum (from a hot, opaque solid, liquid, or gas) passes through a transparent gas at a lower temperature, the cooler gas will cause the appearance of dark lines (absorption lines).

  • Example: Light from the Sun.


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Temperature and Brightness

  • Wien’s Law

  • BlackBody.html


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Wave Nature of Light

  • Diffraction

    • Huygens

    • Light bending around an opaque object

  • Interference

    • Young’s Double slit experiment


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Diffraction

http://www.stsci.edu


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Particle Nature of Light

  • Photoelectric effect

  • Quanta

    • E = hf

  • Lenses


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Lens

http://www.stsci.edu




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Homework 6

  • What are the parts of the electromagnetic spectrum? What part can we see? What everyday objects emit each part of the spectrum?

  • What is the frequency of light that is 6.365X10-10m? (Remember that the speed of light is 3.000X108 m/s)

  • Page 127 CQ 1,2 P 2

  • What is the energy of the particle of light with a wavelength of 6.365X10-10m? (Remember the Heisenberg uncertainty number, h, is 6.63X10-34Js)


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