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 • 1. He discovered the nucleus • 2. Found atom to be mostly empty space. • 3. Knew that the Electrons went around the atom

4. Rutherford’s Failure • He couldn’t explain why the negative electrons aren’t attracted into the positive nucleus, causing the atom to collapse. http://www.colorado.edu/physics/2000/waves_particles/wavpart2.html

5. Neils Bohr Anyone who isn’t shocked by quantum theory doesn’t understand it.

6. What are the components of a wave? • A wave has frequency and wavelength

7. 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

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

9. How do waves differ? • They have different wavelengths • They have different frequencies • They have different energies

10. 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!

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

12. 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

13. 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

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

15. 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

16. 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

17. 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

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

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

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

21. 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.

23. 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.

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

25. 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

26. 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

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

28. 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

29. 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

30. 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

31. 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

32. 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

33. The absorption Spectrum

34. 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.

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

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

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

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

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

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

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

42. 9. W? • a. • b. c. • d.

43. 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