Light and Quantized Energy in Atoms: Wave-Particle Duality and Characteristics

1. Chapter 5.1 Electrons in Atoms: Light and Quantized Energy

2. Bell Ringer – Write question, answer True or False • Light needs air to travel. • Different wavelengths of light have different energy and therefore different speeds. • A radio wavelength is a sound wave not part of the electromagnetic spectrum. • Only shiny materials reflect light. • Shiny objects reflect more light than dull objects

3. 5.1 Light and Quantized Energy • Rutherford’s nuclear model (ch4) lacking • didn’t account for e arrangement in space around the nucleus • didn’t address why - charged e- aren’t pulled into the + charged nucleus • couldn’t explain why diff. elements behave diff.

4. What does light have to do with it? • Scientists noticed that certain elements emit visible light when heated in a flame

5. Items we’re familiar with that make light when heated.

6. Behavior related to electrons • Analysis of the emitted light revealed that element’s chemical behavior is related to the arrangement of electrons.

7. Must first understand light • What is light? • Jot down your ideas on what you think light is in your notebook. • What words can you use to describe light?

8. Is it a wave or a particle?

9. A light wave? Source: http://commons.wikimedia.org/wiki/File:Light_dispersion_conceptual_waves.gif Source: http://www.livescience.com/24509-light-wave-particle-duality-experiment.html A light particle? Source: http://ptc.weizmann.ac.il/_uploads/imagesgallery/489dispersion1.gif

10. Light can behave as both a wave AND a particle. Source: https://www.youtube.com/watch?v=Q_h4IoPJXZw

11. Nature of Light • Light wave: • electromagnetic wave, can be seen by humans • Photon: • elementary particle • all forms of electromagnetic radiation exhibit wave-particle duality • All light travels at a constant speed but its speed can change depending on the medium it travels in • Diff. kinds of light are defined by their wavelength.

12. Light as a WAVE • Electromagnetic Radiation (ER) • form of energy that exhibit wavelike behaviors as it travels through space

14. To help you remember • mnemonic: Raging Martians Invaded ROY G. BIV Using X-ray Guns

15. Visible Spectrum and Color ROYGBIV • Redlight has the longest wavelength and lowest frequency. • Blue light has the shortest wavelength and highest frequency. • White light is the combination of all the colors of the visible light spectrum. • Black is merely the absence of the wavelengths of the visible light spectrum.

16. Radio Waves Radio waves: • longest wavelength • lowest frequency • used for transmission of data • Television • Cell phones • wireless networking • radio

17. Microwaves Microwaves: used in Wi-Fi and microwave ovens to quickly head food.

18. Infrared Waves Infrared waves: produce thermal energy.

19. Visible Light • Visible light: ROYGBIV and wavelength detectable by the human eye.

20. Ultraviolet Ultraviolet waves: emitted by the Sun but most is absorbed by atmosphere; causes sunburn and cancer due to irreparable damage to DNA

21. X-rays • X-rays: can pass through most substances with some absorption which allows see through objects like in diagnostic medical imaging

22. Gamma Rays • Gamma rays: shortest wavelength, highest frequency ; most energetic photons; used for irradiation of food for sterilization, for cancer therapy, and for diagnostic imaging in nuclear medicine.

23. Light as a WAVE • Light is a type of ER We describe light waves using these characteristics: • Wavelength (λ) • distance btwn two crests or troughs (m, cm, nm) [λ – greek letter lambda)

24. Characteristics of light waves • 652 Hz = 652 waves/second = 652 s-1

25. Frequency

26. Characteristics of light waves • Amplitude – height of wave from origin to crest or trough

27. Characteristics of light waves • Speed – all waves travel at the same speed (speed of light) c = 3.00 x 10 8 m/s (in a vacuum) Speed of light = (wavelength)(frequency) c = λ ʋ

28. Speed of light is constant • Since speed of light is constant, that means that in order for the equation to be mathematically true, λ ʋ are inversely proportional.

29. Huh? • Inversely proportional relationship c = λ ʋ 50 = 5 x 10 50 = 10 x 5 10 = 25 x 2 10 = 2 x 25

30. Calculations (pg 121)

31. We Practice

32. You Practice • Pg 121 • Practice Problems # 2 - 4

33. answers

34. Volunteer To Read • Page 122 first paragraph • Particle Nature of Light

35. Particle Nature of Light • Max Planck • Explained emission of light by heated objects (red hot ) • Quantum – minimum amount of energy gained/lost by an atom • Matter can gain or lose energy only in small, specific amounts called quanta and anything outside of these specific amounts do no exist as energy for that specific form of matter. • Equantum = h (h = Planck’s constant = 6.626 x 10-34Js)

36. Particle Nature of Light • Photoelectric effect (explained by Einstein) • Photoelectrons emitted from metal’s surface • ER is both wavelike & particle - like • Photon – particle of ER w/ no mass that carries a quantum of energy

37. Calculations (pg 124) Tiny water drops in the air disperse the white light of the sun into a rainbow. What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 1014s-1? Equantum = h Known: • h = 6.626 x 10-34Js •  = 7.23 x 1014s-1 Unknown: • Equantum = (6.626 x 10-34Js )(7.23 x 1014s-1) = 4.79 x 10-19 J

38. Practice • Page 124 • Practice Problems # 5-6

39. answers 5 a) 4.19 x 10-13 J b) 6.29 x 10-20 J c) 6.96 x 10-18 J 6 a) Gamma ray or x-ray b) Infrared c) ultraviolet

40. Homework • Page 126 • Section assessment • #7 & 12 • Page 146 • #38, 65-70