1. Waves, Particles, and the Spectrum Quantum Theory

2. Learning Objectives TLW understand the electromagnetic spectrum and the mathematical relationships between energy, frequency, and wavelength of light (TEKS 6.B) TLW calculate wavelength, frequency, and energy of light using Planck’s constant and the speed of light (TEKS 6.C)

3. Engagement Activities Cool Cosmos Website

4. I. Intro A. Model of an atom 1. Knowing there are positive (protons) and negative (electrons) particles a) and opposite charges attract b) why aren’t electrons “drawn” into the positive nucleus?

5. 2. Scientists answered that question by a) studying the emission and absorption of light by matter b) there was a definite relationship between light and an atom’s electrons 3. The study of the behavior of light led to energy, matter and atomic structure

6. How it Started Discovery Education web videos– linklink Classical Gas: Classical and Quantum Physics Particles Waving – The Dual Nature of Light and Matter

7. II. Waves and particles A. Waves 1. It was believed light behaved as a wave (until the 1900’s) 2. Visible light is a kind of electromagnetic (em) radiation = energy that travels through space

8. also includes x-rays, microwaves, radio waves, ultraviolet and infrared light 3. Together ALL electromagnetic radiation form the electromagnetic spectrum

10. 4. the properties of a wave give waves their repetitive nature a) Wavelength ( ) - length of one complete wave b) Frequency ( ) - # of waves that pass a point during a certain time period measured in hertz (Hz) = 1/s c) Amplitude (A) - distance from the origin to the trough/crest

11. amplitude crest trough Wave height

12. Longer wavelength Shorter frequency Greater frequency Shorter wavelength

13. 5. Frequency and wavelength are inversely proportional a) b) c = speed of light (3.00 X 10 8 m/s) λ = wavelength (m, cm, nm) v = frequency (Hz) c =

14. 6. Knowing that all electromagnetic radiation travels in waves with each one having a different wavelength and frequency you can determine which type of em radiation there is

15. GIVEN: = ? = 434 nm = 4.34  10 -7 m c = 3.00  10 8 m/s WORK: = c/ = 3.00  10 8 m/s 4.34  10 -7 m = 6.91  10 14 Hz EX: Find the frequency of a photon with a wavelength of 434 nm.

16. B. Particles of light 1. Two experiments led scientists to realize light not only acted as a wave but also as “particles” 2. The photoelectric effect is the emissions from metals when light shines on metal 3.Basically, light knocked electrons off the metal and created an electrical current

17. 3. BUT the light had to be of a certain frequency for the photoelectric effect to take place

18. Discovery Education web video – Max Planck and Black Body Radiation - linklink

19. 4. Max Planck studied the emission of light by hot objects in the 1900’s a) hot objects don’t emit em energy continuously, like in a wave b) instead, em energy is emitted in small, specific amounts called quanta

20. c) quantum = the minimum quantity of energy that can be lost or gained by an atom d) giving us quantum theory Classical Theory = Waves Quantum Theory

21. 5. The energy of the photon is proportional to its frequency a) b) E = energy (J, Joules) h = Planck’s constant (6.6262  10 -34 J·s) v = frequency (Hz) of radiation emitted E = h

22. C. Quantum Theory 1. Albert Einstein (1905) a) He concluded that light has the properties of both waves and particles b) wave-particle duality c) a photon – a particle of electromagnetic radiation

23. The Spectrum

24. A. Line-Emission Spectrum ground state excited state ENERGY IN PHOTON OUT

25. This element gives 435nm, 485nm, 655nm This is the “fingerprint” for hydrogen

26. B. Can electrons have a wave-particle duality? 1. Louis de Broglie in 1924 asked if electrons could have a wave- particle nature. 2. Knew waves confined to a certain space had a certain frequency 3. So, electrons are confined to a certain space, should mean have a certain frequency

27. 4. de Broglies lent support to the quantum model of the atom 5. Proof: VISIBLE LIGHT ELECTRONS

28. 6. The quantum model of an atom

29. 2. Photons a) have zero mass b) carry a quantum of energy c) the energy of a particular photon depends on the frequency of the em radiation

30. D. Conclusion 1. Electrons can only exist at certain, specific distances from the nucleus 2. Orbitals for atomic electrons vary in shape 3. Electrons move very quickly 4. Electrons give off em radiation

31. Group & Independent Practice Lab #20 – Flame Test (link) or see Addison-Wesley lab manual pages 151 - 154link Calculating wavelength, frequency, and energy of light – link link Chemistry Textbook (read pages 372 – 383) –Page 375, Problems 11 & 12 –Page 379, Problems 13 & 14 –Page 383, Problems 15 - 19

32. More Cool Stuff DiscoveryEducation resources linklink