1. 1 Part 02 Quantum Theory

2. 2 Beginning of 20 th century - wave model of light universally accepted - questions still existed that could not be answered using this model, for example, the way EMR was emitted by hot objects - metal heated, emits invisible infrared radiation (heat), but no visible light. - continue heating the metal and it glows red  yellow  white (white-hot) - why are different colors emitted at different temperatures?

3. 3 1.Quantum Theory -designed by Max Planck -states that light energy being given off from a hot body is not emitted continuously -states that energy is given off in discrete amounts or quanta - basis for the currently accepted model of electronic structure Quanta means fixed amount

4. 4 1.Quantum Theory -modified by Einstein -used Planck’s theory to explain the photoelectric effect -light consists of quanta of energy which behave like tiny particles - called these energy quanta photons -energy of the photon depends on the frequency of the light

5. 5 1.Quantum Theory -Planck derived an equation to calculate the energy in one photon or quantum of any type of EMR

6. 6 Wavelength, Lambda, , in meters Frequency, f, Hertz, 1/sec VioletBlueGreenYellowOrangeRed Wavelength, in nanometers 400460540610575700 The Electromagnetic Spectrum Cosmic or Gamma Rays X-RaysUltra- violet Rays Infrared Rays Micro- waves TV Waves FM Radio Waves AM Radio Waves Power and Telephone 10 -16 10 -12 10 -14 10 -11 10 -9 10 -10 10 -8 10 -7 4 x 10 -7 10 -4 10 -6 10 -5 10 -1 10 -3 10 -2 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 24 10 20 10 22 10 19 10 17 10 18 10 16 10 15 10 12 10 14 10 13 10 9 10 1110 10 8 10 7 10 6 10 5 10 4 10 3 10 2 10 1 10 0 7 x 10 -7 to 8 x 10 14 4 x 10 14 Radar Waves The type of radiation depends on its wavelength or frequency. The energy of radiation depends on its wavelength or frequency.

7. 7 2.Calculating the Energy of EMR -for all electromagnetic radiation E photon =hf where E = energy of one photon or quantum where h = Planck’s Constant = 6.626068 x 10 -34 J. sec f = frequency = 6.63 x 10 -34 J. sec

8. 8 Is the relationship between the energy of a photon and the frequency of the electromagnetic radiation direct or inverse? Direct As f gets larger, E gets larger. E photon =hf

9. 9 Example: Calculate the energy of one photon of ultraviolet light having a frequency of 2.2 x 10 16 Hz.

10. 10 E photon = hf =(6.63 x 10 -34 J. sec)(2.2 x 10 16 1/sec) E photon = 1.5 x 10 -17 J

11. 11 Examples: Calculate the energy of one photon of a microwave having a wavelength of 3.5 x 10 -3 m.

12. 12 Is the relationship between the energy of a photon and the wavelength of the electromagnetic radiation direct or inverse? Inverse E is in the numerator; is in the denominator. As gets larger, E gets smaller E photon =hc

13. 13 E photon = hc (6.63 x10 -34 J. sec)(3.00 x10 8 m/sec) E photon =5.7 x 10 -23 J = __________________________ 3.5 x 10 -3 m

14. 14 What type of radiation contains more energy, ultraviolet or microwave? E UVphoton = 1.5 x 10 -17 J E  wavephoton = 5.7 x 10 -23 J E UVphoton is a MILLION times more than E  wave photon.

15. 15 How microwaves cook food? The microwaves contain photons with just enough energy to cause the water molecules in the food to rotate, which creates friction, which produces heat, which cooks the food.

16. 16 Example: Calculate the energy of one photon of yellow light having a wavelength of 580 nm.

17. 17 E photon = hc (6.63 x10 -34 J. sec)(3.00 x10 8 m/sec) E photon =3.4 x 10 -19 J = __________________________ 5.8 x 10 -7 m 580 nmx1 _____ 1 x 10 9 = 5.8 x 10 -7 m nm m

18. 18 Which electromagnetic radiation has more energy in its photons, microwaves or yellow light? Yellow light Yellow light has shorter wavelength hence more energy.

19. 19 Example: Calculate the energy of one photon of an FM radio wave of frequency 100.1 Megahertz.

20. 20 E FMphoton = hf =(6.63 x 10 -34 J. sec) = 6.64 x 10 -26 J 100.1 MHz = 1.001 x 10 8 Hz 1 1 x 10 6 x (1.001 x 10 8 1/sec) E FMphoton MHz Hz

21. 21 Example: Calculate the energy of one photon of a satellite radio wave of frequency 2.3 Gigahertz.

22. 22 E SATphoton = hf =(6.63 x 10 -34 J. sec) = 1.5 x 10 -24 J 2.3 GHz = 2.3 x 10 9 Hz 1 GHz 1 x 10 9 Hzx (2.3 x 10 9 1/sec) E SATphoton

23. 23 What type of radio operates at more energy, FM or satellite? E FMphoton = 6.637 x 10 -26 J E satellitephoton = 1.5 x 10 -24 J E satellitephoton is a HUNDRED times more than E FMphoton.

24. 24 Example: The energy needed to break the bond between the oxygen atoms in an ozone molecule is 8.206 x 10 -19 Joules. Calculate the wavelength in meters of electromagnetic radiation that will break this bond. Identify the type of radiation.

25. 25 E photon = hc (6.63 x10 -34 J. sec)(3.00 x10 8 m/sec) = __________________________ 8.206 x 10 -19 J  = 2.42 x 10 -7 mUltraviolet rays = hc E photon

26. 26 The UV rays from the sun contain photons that have just the right energy to break the bonds in the ozone molecule. The energy is absorbed by the molecules and does not reach the earth. O O O O O O How does the sun affect the ozone layer? O O O The ozone molecules reform and the earth has a continuous protective layer.

27. 27 3.The Photoelectric Effect -Einstein used Quantum Theory to explain the photoelectric effect -won the Nobel Prize in Physics in 1921 -electrons can be ejected from the surface of a substance if they absorb the right amount of photon energy -photon energy depends on the wavelength of the radiation

28. 28 Zinc Ultraviolet Radiation Surface Atoms Photons Energy from the photon kicks an electron off an atom Photon must have exactly the right amount of energy for the electron to eject Only UV light will work e-

29. 29 Zinc Infrared Radiation Surface Atoms Photons Energy from the photon is too small No electron is ejected Only UV light will work e-

30. Dual nature of light Sometimes behaves as a wave (goes the speed of light, not affected by a magnetic field or gravity) Sometimes behaves as a particle (ejects electrons from the surface of metals, is affected by enormous amounts of gravity) 30 Assignment p. 42 (notes): Read p 130-134 http://www.youtube.com/watch?v=yDCCbxCJLlM