…and, in conclusion…

1. …and, in conclusion…

2. You will need to know the contributions of… • Bohr • Planck • Einstein • Heisenberg • de Broglie

3. Q: How is light produced?

4. Q: How is light produced? • A: An excited electron…

5. Q: How is light produced? • A: An excited electron… • loses energy…

6. Q: How is light produced? • A: An excited electron… • loses energy… • as it falls…

7. Q: How is light produced? • A: An excited electron… • loses energy… • as it falls… • from a higher to a lower energy level,…

8. Q: How is light produced? • A: An excited electron… • loses energy… • as it falls… • from a higher to a lower energy level,… • emitting that energy…

9. Q: How is light produced? • A: An excited electron… • loses energy… • as it falls… • from a higher to a lower energy level,… • emitting that energy… • as a photon of light

10. Excited * * An electron that gains energy is excited: moves to a higher energy level, physically moves away from nucleus An electron in its normal position is in its ground state (gains energy) Ground state

11. Excited * * • Light is produced As it loses energy Ground state

12. We use a * to mark an excited electron or atom. • An atom can be excited by:

13. We use a * to mark an excited electron or atom. • An atom can be excited by: Heat(light bulbs, stars, sparks, flames) Electricity(sparks, fluorescent bulbs) or Chem. rxns(lightning bugs, glow sticks)

14. Let’s do the wave.

15. The wave equation Where c is the speed of light, 3.00 x 108 m/s l is the wavelength (the symbol, lambda, is the Greek “l” for length) and n is the frequency (the symbol, nu, is the Greek “n”) c=ln

16. Please notice: • Wavelength and frequency are inversely related. • When wavelength increases, frequency decreases.

17. Q: What is the frequency of light that has a wavelength of 570 nm(5.7x10-7m)?

18. Q: What is the frequency of light that has a wavelength of 570 nm(5.7x10-7m)? • c=ln

19. Q: What is the frequency of light that has a wavelength of 570 nm(5.7x10-7m)? • c=lnn=c/l

20. Q: What is the frequency of light that has a wavelength of 570 nm(5.7x10-7m)? • c=lnn=c/l=(3.00x108m/s) / (5.7x10-7m)

21. Q: What is the frequency of light that has a wavelength of 570 nm(5.7x10-7m)? • c=lnn=c/l=(3.00x108m/s) / (5.7x10-7m) • 5.3 x 1014 /s =5.3 x 1014 Hz

22. Next: Planck’s equation • The energy of a photon is directly related to its frequency E=hn • where • E is the energy (in Joules), • n is the frequency (in waves/s, or Hz), and • h is the conversion factor, Planck’s constant. h=6.63 x 10-34 Js

23. The electromagnetic spectrum

24. For any pair-- Which has greater l, n, E, v?

25. The electromagnetic spectrum Increasing wavelength Increasing frequency Increasing energy and, c is the velocity of light (c for constant!)

26. Visible light Short wavelength High energy High frequency 400 nm Long wavelength Low energy Low frequency 700 nm

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34. The Bohr Model of the atom • Bohr’s solar system model -- shows why the H gives off only 4 wavelengths of visible light. • He calculated the energy that the electrons did give off, and the differences in energy.

35. Bohr drew a picture like this Electron loses energy Electron gains energy

36. Visible wavelengths produced by hydrogen atoms • These 4. No more. There is nothing between the levels– no “half-transitions”

37. In the hydrogen spectrum • The wavelengths are: • 410 nm (violet) • 434 nm (blue) • 486 nm (green) • 656 nm (red)

38. In the hydrogen spectrum 4.85x10-19J 4.58x10-19J 4.09x10-19 J 3.03x10-19J

39. In the hydrogen spectrum 4.85x10-19J 4.58x10-19J 4.09x10-19 J 3.03x10-19J What is the energy difference between these two levels?

40. In the hydrogen spectrum 4.85x10-19J 4.58x10-19J 4.09x10-19 J 3.03x10-19J What is the energy difference between these two levels? .49 x 10-19 J

41. These energies represent the differences in the energy levels… …and that’s how we know where the energy levels are.

42. Other phenomena that teach us about electrons and light The photoelectric effect • Described by Einstein for his Nobel prize • Light knocks electrons off a metal • Indicates the particle nature of light One photon excites one electron

43. Other phenomena that teach us about electrons and light • Heisenberg’s Uncertainty Principle • “You cannot determine both the location and momentum of a particle exactly.” • If you measure one, you change the other unpredictably • Leads to the wave and particle natures of everything

44. Gratuitous joke Heisenberg was pulled over on the highway. The officer asks, “Do you know how fast you were going?” Heisenberg replies,

45. Gratuitous joke Heisenberg was pulled over on the highway. The officer asks, “Do you know how fast you were going?” Heisenberg replies, “No, but I do know where I am!”

46. Other phenomena that teach us about electrons and light • DeBroglie’s wavelength • Describes the wave nature of particles • Considers the uncertainty in position as a wavelength

47. Electron Configurations …and now, the rest of the story

48. Fe (2,8,14,2) • --An electron configuration (EC) shows the location of all electrons in an atom or ion. • --In an atom, number of electrons = number of protons = atomic number • --Electrons are found around the nucleus of an atom in specific energy levels.

49. Levels have sublevels!

50. Levels have sublevels! Sublevels have orbitals!