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Electromagnetic Radiation

Electromagnetic Radiation. Energy can travel through space as a form of kinetic energy we call electromagnetic radiation. Consists of electric and magnetic fields that vary repetitively. Most obvious to us: visible light. Emission Spectrum.

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Electromagnetic Radiation

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  1. Electromagnetic Radiation • Energy can travel through space as a form of kinetic energy we call electromagnetic radiation. • Consists of electric and magnetic fields that vary repetitively. • Most obvious to us: visible light

  2. Emission Spectrum • Ideas about arrangements of atoms have come mostly from emmision spectra. • Emission Spectra are bright lines produced on film by radiation that has passed through a glass prism after being emitted from electrically or thermally excited atoms.

  3. EM Radiation • Can be described in terms of waves… • Wavelength • Frequency • Speed of Light

  4. Electromagnetic Radiation • All light travels at the same speed: 2.9979 x 108 m/s. How are wavlength, frequency, and c related? wavelength (frequency) = speed of light Symbols…

  5. Electromagnetic Radiation • Because all photons travel at the same speed, the difference between two photons corresponds to a difference in a quality commonly referred to as “wavelength”. • We are looking at light particles (photons) that behave as waves.

  6. Light is a Wave • A DVD has thousands of small ridges only hundreds of nanometers in width. These ridges diffract light of different wavelengths to a different extent. • The rainbow pattern we see is a consequence of the wave nature of light.

  7. Calculations… Light near the middle of the UV region of the Electromagnetic spectrum has a frequency of 2.73*1016 s-1 Yellow light near the middle of the visible spectrum has a frequency of 5.26*1024s-1 Calculate the wavelength that corresponds to these two frequencies.

  8. Continuous Spectrum • Light from the Sun and other incandescent sources contains a mixture of photons of different wavelengths. • The different colors we see are a result of this difference in energy between two photons. • When light from the sun is diffracted (separated) it forms a continuous spectrum, which is a rainbow • Using a spectroscope, look at the projector screen. Can you see a continuous spectrum?

  9. The Complete Electromagnetic Spectrum • The spectrum visible to the human eye ranges from about 700-400 nm • The complete electromagnetic spectrum ranges thousands of times bigger and smaller. • Only a very small portion is visible to the eye

  10. The Complete Electromagnetic Spectrum • In order from low to high energy: • Radio Waves • Microwaves • Infrared Radiation • Visible Light • Ultraviolet Radiation • X-Rays • Gamma Rays

  11. Particle Behavior of Photons • According to Max Planck each photon of light has a particular quanta of energy. • This energy depends on the frequency. Energy = Planck’s Constant ( frequency) Symbols…

  12. Calculation Cont. We have already calculated the wavelength. Now, calculate the energy, in Joules, of an individual photon of each. Compare the two energies by calculating the energy of each.

  13. UV vs. Visible Light Energy UV Light = 1.81*10-17 J Visible Light (yellow) = 3.49*10-19 J Ratio = Euv/ Evis Ratio = 1.81*10-17 J/ 3.49*10-19 J Ratio = 51.9 So, why might UV light be so harmful to our skin?

  14. Bohr’s Atomic Model (aka Planetary model) • Bohr used his observations to argue that the energy of an electron is "quantized” • Meaning only certain quantities of energy are allowed therefore restricting its location of the electron to certain regions around the nucleus • Since only certain energy levels are allowed it is actually possible to diagram the atom in terms of its energy levels.

  15. Electron Transitions “Rest (Ground) State”

  16. Electron Transitions “Excited State”

  17. Electron Transitions “Rest (Ground) State”

  18. Gas Emission Tubes

  19. The Chords of Neon The individual lines correspond to the energy difference between two orbitals. Using the entire set of lines, we can figure out the relative arrangement of the energy levels and therefore the element.

  20. Gas Tubes • Neon • Hydrogen • Chlorine

  21. Make your own EM spectrum… Obtain a piece of paper and draw your own EM Spectrum…

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