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I. Waves & Particles

Ch. 5 - Electrons in Atoms. I. Waves & Particles. Properties of Waves. Many of the properties of light may be described in terms of waves even though light also has particle-like characteristics. Waves are repetitive in nature. A. Waves. Wavelength ( ) - length of one complete wave

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I. Waves & Particles

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  1. Ch. 5 - Electrons in Atoms I. Waves & Particles

  2. Properties of Waves • Many of the properties of light may be described in terms of waves even though light also has particle-like characteristics. • Waves are repetitive in nature

  3. A. Waves • Wavelength () - length of one complete wave • Frequency () - # of waves that pass a point during a certain time period • hertz (Hz) = 1/s • Amplitude (A) - distance from the origin to the trough or crest

  4. crest A A origin trough  A. Waves greater amplitude (intensity) greater frequency (color)

  5. Electromagnetic Radiation • Electromagnetic radiation: (def) form of energy that exhibits wavelike behavior as it travels through space • Types of electromagnetic radiation: • visible light, x-rays, ultraviolet (UV), infrared (IR), radiowaves, microwaves, gamma rays

  6. Electromagnetic Spectrum • All forms of electromagnetic radiation move at a speed of about 3.0 x 108 m/s through a vacuum (speed of light) • Electromagnetic spectrum: made of all the forms of electromagnetic radiation

  7. B. EM Spectrum HIGH ENERGY LOW ENERGY

  8. R O Y G. B I V red orange yellow green blue indigo violet B. EM Spectrum HIGH ENERGY LOW ENERGY

  9. Ionizing radiation • Subatomic particles or electromagnetic waves energetic enough todetach electrons from atoms or molecules, ionizing the atoms or molecules. GlossaryEntry I Gamma rays, X-rays, high energy ultraviolet light, alpha particles, and beta particles are examples of ionizing radiation.

  10. B. EM Spectrum • Frequency & wavelength are inversely proportional c =  c: speed of light (3.00  108 m/s) : wavelength (m, nm, etc.) : frequency (Hz)

  11. WORK:  = c   = 3.00  108 m/s 4.34  10-7 m B. EM Spectrum • EX: Find the frequency of a photon with a wavelength of 434 nm. GIVEN:  = ?  = 434 nm = 4.34  10-7 m c = 3.00  108 m/s = 6.91  1014 Hz

  12. C. Quantum Theory • Photoelectric effect: emission of electrons from a metal when light shines on the metal • Hmm… (For a given metal, no electrons were emitted if the light’s frequency was below a certain minimum – why did light have to be of a minimum frequency?)

  13. C. Quantum Theory • Planck (1900) • Observed - emission of light from hot objects • Concluded - energy is emitted in small, specific amounts (quanta) • Quantum - minimum amount of energy change

  14. Classical Theory Quantum Theory C. Quantum Theory • Planck (1900) vs.

  15. C. Quantum Theory • Einstein (1905) • Observed - photoelectric effect

  16. C. Quantum Theory • The energy of a photon is proportional to its frequency. E: energy (J, joules) h: Planck’s constant (6.6262  10-34 J·s) : frequency (Hz) E = h

  17. C. Quantum Theory • EX: Find the energy of a red photon with a frequency of 4.57  1014 Hz. GIVEN: E = ?  = 4.57  1014 Hz h =6.6262  10-34 J·s WORK: E = h E = (6.6262  10-34 J·s) (4.57  1014 Hz) E = 3.03  10-19 J

  18. C. Quantum Theory • Einstein (1905) • Concluded - light has properties of both waves and particles “wave-particle duality” • Photon - particle of light that carries a quantum of energy

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