Electromagnetic Radiation and the Bohr Model of the Atom

1. Electromagnetic Radiation and the Bohr Model of the Atom Objective: Students will understand the Bohr model of the atom by understanding light.

2. Review: Rutherford’s Model

3. Rutherford’s Contributions • the nucleus of the atom is composed of protons and neutrons. • That the nucleus is small • The electrons are circling the nucleus.

4. Rutherford’s Failure • He couldn’t explain why the negative electrons aren’t attracted into the positive nucleus, causing the atom to collapse. • Video 15:15

5. A Strange Answer to a Strange Question • Why doesn’t the electron fall into the nucleus? • Because it isn’t allowed! To understand this unbelievable phenomenon, we must understand the nature of light

6. Neils Bohr We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct. My own feeling is that it is not crazy enough.

7. What are the components of a wave? • A wave has frequency, amplitude and wavelength

8. Frequency • The # of peaks that pass by in a given amount of time • Hz = 1/sec • MHz = 1,000,000/sec • KHz = 1,000/sec

9. Electromagnetic Radiation Name Several Types of electromagnetic Radiation(325)

10. How do waves differ? • They have different wavelengths • They have different frequencies • They have different amplitudes

11. How are they different? • They have different frequencies • They also have different energies Click here to see how they differ Then here to see how they are the same!

12. What do they all have in common? • They all travel at the speed of light • 3.00 x 108 meter/sec

13. Wavelength and Frequency • If the λ = 2 meters and υ = 10/sec, find the speed • λ x υ = speed • 2 meters x 10/sec = 20.0 meters/sec • 5 meters x ______ = 20.0 meters/sec • So frequency and wavelength are inversely proportional

14. KSL Radio’s Wavelength • KSL broadcasts at 1160 KHz. Find the λ of KSL’s signal. • 1160KHz = 1160000 /sec • Wavelength x frequency = speed • λ x 1160000 = 3.0 x108 m/sec (3.0 x108 m/sec)/(1160000/sec) = 258 meters

15. FM or AM

16. What is a Photon • Photons are light particles. A bundle of energy

17. Energy of Photons • The energy of a photon is given by this equation E = υ h. • The symbol “h” represents Planck’s constant. It has a value of

18. KSL 1160 • Find the Energy of a photon of light produced by KSL (1160 KHz) • E = υ h • E = 1160000 s-1 x 6.626 x 10-34 Js • E = 7.69 x 10-28 J

19. Energy and Frequency • How are Energy and υ related? • The higher the frequency the greater the energy. • How are Energy and λ related? • The lower the energy the longer the λ

20. Radio Waves • Turn your book to page 325. What is the electromagnetic with the lowest energy?

21. Who or what is Roy G Biv? • An acronym for the colors of the rainbow. It is not a person.

22. Hydrogen and Roy G Biv • The colors emitted when energy is passed through hydrogen is

23. The Quantum Atom • Atoms are quantized because they only emit light at certain frequencies and energies. • A Quantum is the smallest quantity of radiant energy, equal to Planck's constant times the frequency of the associated radiation. • E = h x frequency

25. A Staircase Not a Ramp • Look at pg 330 Figure 11.15. Like a staircase, the atom has specific energies. A ramp has infinitely small divisions.

26. What Does “N” represent? • The Energy Levels inside the atom

27. What values can N have • 1, 2, 3, …. • In the hydrogen atom, where does the electron reside? • In the lowest energy level or n=1 • The electron can move up to higher energy levels by absorbing photons. • We then say the electron is excited

28. A relaxing electron • What happens when an electron relaxes? • It falls from a high energy level to a lower one. • What happens to the extra energy? • It is emitted in the form of light. • The further an electron falls the more energy it gives off

29. What Gives off the Most Energy? Higher Energy Lower Energy

30. Finding the energy of n=3 • The equation to find the energy of the hydrogen energy levels is • E = -2.178 x 10-18 J (1/N2) • E = -2.178 x 10-18 J (1/32) • E = -2.42 x 10-19 J

31. Finding the difference between n=2 and n=3 • For N=2, E = -5.45 x 10-19 J • For N=3, E = -2.42 x 10-19 J • What happens if an electron falls from N=3 to N=2? • Just take n=2 and subtract n=3, that gives you ΔE • ΔE = 3.0 x 10-19 J

32. Calculate the υ • E = υ h • 3.03 x 10-19 J = υ h • 3.03 x 10-19 J = υ x 6.626 x 10-34Js • υ = 4.57x 1014 Hz • λ x υ = 3.03 x 108 meters/sec • λ x 4.57x 1014 = 3.0 x 108 meters/sec • λ = 6.56 x 10-7 meters

33. The Lyman and Balmer series • If an electron falls to n=1, the energy is to high for us to see. • It can be detected but it falls into the UV spectrum

34. Ultra Violet, Infra Red, Visible • Where the electron falls to determines the type of light it produces. • If it falls to the n=3, it produces IR. • We can only se it if it falls to the n=2

35. The absorption Spectrum

36. Quiz #1 • 1. What was the shortcoming of the Rutherford model of the atom? • a. It couldn’t explain how the electron stayed in orbit. • b. It couldn’t explain the existence of electrons. • c. It couldn’t explain the existence of protons.

37. 2. Who improved the Rutherford model? • a. Dalton • b. JJ Thompsonc. Neils Bohr • d. Max Plank

38. 3. Who is the constant “h” named after? • a. Dalton • b. JJ Thompsonc. Neils Bohr • d. Max Plank

39. 4. Which has the longest wavelength? • a. Red Light • b. UV Lightc. IR Light • d. Violet Light

40. 5. Which form of electromagnetic energy has the most energy? • a. Red Light • b. UV Lightc. IR Light • d. Violet Light

41. 6. Which element’s spectrum did Bohr explain? • a. Helium • b. Hydrogenc. Carbon • d. Oxygen

42. 7. Which has the lowest energy in the visible spectrum? • a. Red Light • b. UV Lightc. IR Light • d. Violet Light

43. 8. Who found energy levels in the atom? • a. Dalton • b. JJ Thompsonc. Neils Bohr • d. Max Plank

44. 9. W? • a. • b. c. • d.

45. 10. Which electronic transition gives off the most energy in the hydrogen atom? • a. N2 to N1 • b. N3 to N2c. N4 to N3 • d. N4 to N2