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Spectral Lines

Spectral Lines. 3.2. Spectral Line formation?. Electron has different energy levels: Floors in a building . Lowest is called the Ground State . Higher states are Excited States. Changing Levels. If you add the RIGHT amount of energy to an atom, the electron will jump up energy floors.

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Spectral Lines

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  1. Spectral Lines 3.2

  2. Spectral Line formation? • Electron has different energy levels: Floors in a building. • Lowest is called the Ground State. • Higher states are Excited States.

  3. Changing Levels • If you add the RIGHT amount of energy to an atom, the electron will jump up energy floors. • If the electron drops down energy floors, the atom gives up the same amount energy. • From before, LIGHT IS ENERGY: E = hc/l

  4. Kirchhoff’s Laws • Light of all wavelengths shines on an atom. • Only light of an energy equal to the difference between “floors” will be absorbed and cause electrons to jump up in floors. • The rest of the light passes on by to our detector. • We see an absorption spectrum: light at all wavelengths minus those specific wavelengths.

  5. Kirchhoff’s Laws Cont… • Excited electrons, don’t stay excited forever. • Drop back down to their ground floors. • Only light of the precise energy difference between floors is given off. • This light goes off in all directions. • From a second detector, we see these specific energy wavelengths: an emission spectrum.

  6. Continuum, Absorption, Emission

  7. Emission Lines • Every element has a DIFFERENT finger print.

  8. Emission and Absorption spectra • The lines represent jumps or leaps from one energy level to another • Lines can be sharp or blurry • Blurry lines were later discovered to be a group of very close lines…some energy levels were very close in energy yet different • Later some of the blurry lines were found to respond to magnetic fields….implication is that orbits have 3-D orientation in space

  9. Balmer equation • 1/λ= RH (1/nf2 – 1/ni2) • Correctly predicts all the 4 lines for the hydrogen atom (only hydrogen) • λ= wavelength of light in metres • RH- Rydberg constant 1.10 x 107 m-1 • nf= final energy level (once returned) • ni= initial energy level (once excited)

  10. Blackbody radiation- Planck • First result after Bohr that was problematic for physicists • A blackbody is a solid object that is heated until it begins to glow (first red then blue then white hot) and then allowed to return to thermal equilibrium slowly • If the intensity or brightness of the different colours that is emitted is plotted a BELL shaped curve is seen…not what was expected!

  11. Blackbody radiation

  12. Interpretation • Higher energy (UV) has a higher peak, lower ernergy (IR) has a lower peak • According to classical physics, it should not be bell shaped but should be a exponential decay kind of curve. Starting high up on the left and going down and to the right like a hockey stick • That means that light emitted from a cooling object is like light, it is made up of chunks like light is made of particles called photons. • Einstein concurred and interpreted the results as meaning energy comes in quanta

  13. Planck and Einstein • E= hf = hc/λ • Energy of the photon of light (J) • h= Planck’s constant 6.63 x 10-34Js or 4.14 x 10-15 eVs • c= speed of light (3.00 x 108 m/s) • λ= wavelength of light (m)

  14. Photoelectric Effect Simulation

  15. Explanation of Photoelectric Effect • In the photoelectric effect, electrons of metals are ejected when light shines on them • However, not all wavelengths of light will cause the photoelectric effect • Red light has no photoelectric effect on potassium • Yellow light causes this effect on potassium

  16. Illustrations of Photoelectric Effect

  17. Wavelength of light is critical

  18. What does it mean? • Einstein interpreted the results and said that energy at the atomic level is in chunks. Only certain energies are allowed • The intensity of the light affects how many electrons jump but does not affect the speed of the electrons once they leave the surface • Frequency (and wavelength) are key. Threshold frequencies are observed for different materials • Minimum energy required to bump an electron off its orbit. If more is delivered, the electron leaves with a faster speed from the surface • Energy is quantized (quanta) • (Photoelectric effect like solar panel!)

  19. Double slit experiment • Results indicated that light which was supposed to be a particle was behaving as a wave • Diffraction of the electrons through the double slit matches wave patterns. • Electron is not a particle but a smear. It’s location cannot be known for certain unless you measure it. • Einstein (God does not play dice) • Bohr (Do not tell God what to do)

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