Exploring Electromagnetic Radiation: Chapter 6

1. wavelength Visible light Amplitude wavelength Node Ultraviolet radiation Chapter 6: Electromagnetic Radiation

4. Short wavelength --> high frequency high energy Long wavelength --> small frequency low energy

5. The electromagnetic spectrum.

7. Which has the longest wavelength? • Infrared • Ultraviolet • X-rays • Radio waves

8. Rank the following in order of increasing frequency: microwaves radiowaves X-rays blue light red light UV light IR light

9. Waves have a frequency • Use the Greek letter “nu”, , for frequency, and units are “cycles per sec” • All radiation:  •  = c • c = velocity of light = 3.00 x 108 m/sec • Long wavelength small frequency • Short wavelength high frequency

10. In a vacuum, the speed of light, c, is 3.00 x 108 m/s. Therefore, The Wave Nature of Light • The product of the frequency, n (waves/sec) and the wavelength, l (m/wave) would give the speed of the wave in m/s. • So, given the frequency of light, its wavelength can be calculated, or vice versa.

11. The Wave Nature of Light • What is the wavelength of yellow light with a frequency of 5.09 x 1014 s-1? (Note: s-1, commonly referred to asHertz (Hz) is defined as “cycles or waves per second”.) • If c =nl,then rearranging, we obtainl = c/n

12. The Wave Nature of Light • What is the frequency of violet light with a wavelength of 408 nm? • If c =nl,then rearranging, we obtainn = c/l.

13. What is the wavelength of WONY? What is the wavelength of cell phone radiation? Frequency = 850 MHz What is the wavelength of a microwave oven? Frequency = 2.45 GHz

14. Quantization of Energy Light acts as if it consists of particles called PHOTONS,with discrete energy. Energy of radiation is proportional to frequency E = h •  h = Planck’s constant = 6.6262 x 10-34 J•s

15. E = h •  Relationships:

16. Short wavelength light has: • High frequency and low energy • High frequency and high energy • Low frequency and low energy • Low frequency and high energy

17. Rank the following in order of increasing photon energy: microwaves radiowaves X-rays blue light red light UV light IR light

18. Energy of Radiation What is the frequency of UV light with a wavelength of 230 nm? What is the energy of 1 photon of UV light with wavelength = 230 nm?

19. What is the energy of a photon of 525 nm light? • 3.79 x 10-19 J • 4.83 x 10-22 J • 3.67 x 1020 J • 8.43 x 1023 J

20. Radio Wave Energy • What is the energy of a photon corresponding to radio waves of frequency 1.255 x 10 6 s-1?

21. What is the energy of a mole of 230 nm photons? Can this light break C-C bonds with an energy of 346 kJ/mol?

22. Does 1200 nm light have enough energy to break C-C bonds?

23. Where does light come from? • Excited solids emit a continuous spectrum of light • Excited gas-phase atoms emit only specific wavelengths of light (“lines”)

24. Light emitted by solids

25. Light emitted by hydrogen gas

26. The Bohr Model of Hydrogen Atom • Light absorbed or emitted is from electrons moving between energy levels • Only certain energies are observed • Therefore, only certain energy levels exist • This is the Quanitization of energy levels

27. Emission spectra of gaseous atoms • Excited atoms emit light of only certain wavelengths • The wavelengths of emitted light depend on the element.

28. Line spectra of atoms

29. Energy Adsorption/Emission

30. Constant = 2.18 x 10-18 J For H, the energy levels correspond to: Energy level diagram:

31. Each line corresponds to a transition: Example: n=3  n = 2

32. Explanation of line spectra Balmer series