Ch. 4 Section 1: Electromagnetic Radiation

1. Ch. 4 Section 1: Electromagnetic Radiation The Colors of Life

2. Bell Work • On a half sheet of paper labeled Bell Work answer the following question. • Think about your weekend, what was one thing you did that involved chemistry?

3. Pre-Assessment • This is NOT for a grade. • Do not panic • This is strictly for me

4. Observe the Pictures below

5. What did the pictures have in common? • They are all forms of ELECTROMAGNETIC RADIATION. • Form of energy that exhibits wavelike behavior as it travels through space • Which means they all involve WAVES.

6. Activity: String waves • Hold the string on each end. • One group member needs to hold their end still, while the other moves the string. • Move the string at varying speeds, height, directions etc. • Observe what happens when you change the wave. • Draw 3 different waves on a sheet of notebook paper. Describe your waves by noting what was changed.

7. Parts of a wave Crest Wavelength Amplitude Trough

8. Frequency

9. VOcab • Electromagnetic Radiation: form of energy that exhibits wave like behavior • Wavelength (λ): distance between corresponding points on adjacent waves. Expressed in distance units, Typically meters(m) • Frequency (ν): number of waves that pass a given point in a specific time, usually 1 second. Expressed in waves per second or Hertz(Hz)

10. EXIT Slip • On a half sheet of paper labeled EXIT SLIP, sketch the following and answer the question. • Draw a wave that has high frequency and low amplitude. • How are frequency and wavelength related?

11. Bell Work • Answer question on a half sheet. • Turn to page 92 in your textbook • Refer to Figure 1.2 and answer the critical thinking questions • Be sure to explain your answers

12. Review • What is electromagnetic radiation? • What is wavelength? • What is frequency? • How are frequency and wavelength related to one another?

13. Electromagnetic Spectrum Activity • Working in groups, read the cards and determine where they may lay on the wave provided. • Place the cards along the spectrum. • When you are done, check your work with another group.

14. Electromagnetic Spectrum

15. Research: visual light spectrum • Using a Chromebook, research the visual light spectrum. • Create a visual representation using color of the visual light spectrum on piece of notebook paper. • Label the wavelengths associated with each color. • You can work in group, but you each need your own paper.

16. Visual Light Spectrum R O Y G B I V IOLET EL LOW NDI GO LUE ED RANG E REEN

17. If the wavelength increases and the frequency decreases, what sort of proportional relationship do these have? • Inversely proportional • Can we determine an equations that could be used to solve for each due to this type of proportional relationship? • The product of these two will be constant

18. The speed of Light • Represented by c • Equal to 3.0 x • Constant for all electromagnetic radiation

19. Applying Math • Since c is a constant and frequency and wavelength are inversely proportional to one another, we can create the mathematical relationship of: C=λν Frequency Wavelength Speed of light

20. Units Speed of light: Wavelength: m or nm Frequency: s-1or Hz C=λν 3.0 x = m (waves/s or s-1or Hz) *note s-1 is equal to 1/s If you are given wavelength in nm, you have to convert to meters before solving.

21. Bell Work 1. Arrange the following types of electromagnetic radiation in order of increasing frequency. a. infrared c. visible light e. microwaves g. X Rays b. gamma rays d. radio waves f. ultraviolet 2. What is the wavelength of the radiation whose frequency is 5.00x1015s-1? In what region of the electromagnetic spectrum is this radiation?

22. Bell Work • For the first 15 minutes, study for your quiz and work on your vocab. This will be your only designated time today to work on the vocab. • Once the quiz is over, we will go over the practice problems.

23. 4.1: Practice Problems 3. What is the frequency of radiation with a wavelength of 5.00x10-8m? In what region of the electromagnetic spectrum is this radiation? 6.00x1015Hz; ultraviolet 4. What is the wavelength of radiation with a frequency of 1.50x1013 Hz? Does this radiation have a longer or shorter wavelength than red light? 2.00x10-5m; longer 5. Suppose that the FM radio station 92.1 broadcasts at a frequency of 92.1 MHz. What is the wavelength in meters of the radiation from the station? Hint: 1MHz = 106Hz 3.26m 6. An inexpensive laser that is available to the public emits light that has a wavelength of 670nm. What is the frequency of the radiation? Hint: 1m = 109nm What is the color of the laser? 4.5x1014Hz; Red

24. Photoelectric Effect • Emission of electrons from a metal when light shines on the metal • Discovered early 1900s • Involved the frequency of the light striking the metal • No electrons were emitted if the light’s frequency was below a certain minimum regardless of light’s intensity

25. Description of light • German physicist, Planck, studied the emission of light by hot objects • Proposed that hot object does not emit electromagnetic energy continuously, as expected • He suggested that objects emit energy in quantum, minimum quantity of energy that can be lost or gained by an atom

26. Quantum of Energy Frequency Energy E=hν Planck’s Constant 6.626 x J•s

27. Dual-Wave Particle • Einstein expanded on Planck’s theory by introducing that electromagnetic radiation has DUAL WAVE-PARTICLE nature. • Thought of light as a stream of particles • Particles called PHOTONS: particle of electromagnetic radiation having zero mass and carrying a quantum of energy • Proposed that electromagnetic radiation is absorbed by matter in whole numbers of photons • Electron must be struck by a single photon possessing at least the minimum energy required to knock the electron loose. • Different metals require different amounts of energy

28. Energy of a Photon Frequency Energy of photon E(photon)=hν Planck’s Constant 6.626 x J•s The minimum energy corresponds to the minimum frequency. If the frequency is below the minimum, the electron will remain bound to the metal surface.

29. Bell work • Work on 4.1 Practice Problems 8-10

30. 4.1: Practice Problems 7. What is the energy of a photon whose frequency is 2.22x1014s-1? 1.47x10-19J 8. What is the frequency of a photon whose energy is 6.00x10-15J? 9.06x1018s-1 9. What is the wavelength of blue light with a frequency of 8.3 x 1015hz? What is the energy of a photon? 3.6x10-8m; 5.5x10-18J 10. What is the frequency of red light with a wavelength of 4.2 x 10-5 m? What is the energy of a photon? 7.1x1012s-1; 4.7x10-21J

31. Electrons exist in two states • Ground State: lowest energy state of an atom • Excited State: state in which an atom has a higher potential energy that its ground state

32. Continuous Spectrum • It was expected that no matter what amount of energy was added to atom, it would become excited. • Continuous Spectrum: continuous range of frequencies of electromagnetic radiation • However, it was found that when an atom fell to its ground state or to a lower-energy level than the excited state, it emitted a photon. • This energy is equal to the difference in energy between the atom’s initial state and its final state.

33. White light through a prism • White light is a combination of ALL colors in the visual light spectrum • When passed through a prism, the colors are separated into color bands

34. Identifying elements • When a light is not white, it will show different results. • By heating a gas with electricity, it gives off colors and by passing this light through a prism, we can identify unknowns • Just like we talked about earlier, each element is unique and will show their own bands when passed through a prism (emission-line spectrum)

35. Bohr’s Model of the Hydrogen atom • Danish physicist, Niels Bohr, proposed a hydrogen-atom model that linked the atom’s electron cloud to photon emission • Electrons circle the nucleus only in allowed paths or orbits • When in these orbits, the atom has a definite, fixed energy. • The closer to the nucleus, the lower the energy

36. Bohr’s Model • Just like the rungs of a ladder, you can calculate your potential energy when standing on the first, second, third, and so on rung. • However, you can’t just float in mid-air so neither can the electrons. They have to be on a path. • Unlike a ladder though, levels are not evenly spaced. Higher energy levels are closer together.

37. Bohr Model • Emission: when an electron falls from the excited state to a lower energy level, a photon is emitted • Taking a step down the ladder • Absorption: when an electron moves from a lower energy level to a higher energy level • Stepping up a rung on the ladder

38. Bohr’s Model Video

39. Changing the energy • What things can change the energy of an electron and move it to a higher energy level? • Heat, electricity, light • Electron becomes excited

40. Changing Energy • What does an atom give off when it falls to a lower energy state? • Light • Each step has a different energy • The further they fall, more energy is released and the higher the frequency.

41. Changing Energies Hydrogens Line-Emission Spectrum 1. Lyman series: ultraviolet 2. Balmerseries: visible 3. Paschenseries: infrared

42. LAB Monday and Wednesday • Dress appropriately for lab • Closed toed shoes • Long pants • No baggy clothes • For long hair, bring a hair tie