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Chemistry: Chapter 4-1 Development of a New Atomic Model

Explore the development of the atomic model, from classical wave behavior to the particle nature of light. Learn about electromagnetic radiation, the photoelectric effect, and quantum energy states of electrons.

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Chemistry: Chapter 4-1 Development of a New Atomic Model

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  1. Chemistry: Chapter 4-1 Development of a New Atomic Model St. Augustine Preparatory School September 4, 2015

  2. Waves • Waves have both wavelength and frequency

  3. Light as a wave Light reflects and refracts as we would expect to see from waves Light also constructively and destructively interferes

  4. Formula for Electromagnetic Radiation (EMR) c = λv c = speed of light = 3.00 x 108 m/s λ = wavelength (in meters) v = frequency (in Hertz) Hertz is a unit that is the same as s-1 or *The actual speed of light is 299 792 458 m/s λ is a Greek symbol named lambda

  5. Examples • Given a wavelength of 3.2 x 10-9m, calculate the frequency of this wave. • If a wave has a frequency of 40 000.Hz, what is the wavelength of the light?

  6. Light as more than a wave The photoelectric effect showed that light behaved as more than a wave Random fact: Einstein published four papers in 1905. These are now titled the Annus Mirabilis (latin: wonderful year) papers. Special relativity was one of these papers. Einstein would win the Nobel prize in Physics in 1921, mainly for the photoelectric effect.

  7. Photoelectric Effect • Lights were shone on metals which caused electrons to leave the metal • The electrons left the metal and went to a collectorwhere the velocity of the electrons was measured • Originally thought that the higher the intensity, the move velocity the electrons will have

  8. Photoelectric Effect • However, intensity had no effect on the velocity of electrons • With waves, intensity is proportional to amplitude • Amplitude was changed and it made no effect • In fact, below a certain frequency of light, no matter what the intensity of the light was, there were no electrons given off

  9. Light as a Particle • Einstein suggested that light travels in photons or little packets of energy. • In order for an electron to be emitted, it must be hit by a single photon of light with enough energy, which depends on frequency E=hv E = energy of photon (joules) h = Planck’s Constant (6.626x10-34Js) v = frequency (Hz)

  10. Example Ultraviolet light has a frequency of 3.2x1017Hz. What quantity of energy is associated with this frequency? A photon of visible light (depending on the color) has an energy of 3.5x10-19J. What frequency would this photon have?

  11. Electrons exist in specific energy states • Ground State: The state of the lowest energy of an atom • In a ground state, all electrons are in the lowest possible energy level • Excited State: is when an electron has a higher potential than it has in its ground state • When an atom returns to its ground state, it gives off its extra energy in the form of light.

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