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

Chemistry: Chapter 4-1 Development of a New Atomic Model. St. Augustine Preparatory School September 4, 2015. Waves. Waves have both wavelength and frequency. Light as a wave. Light reflects and refracts as we would expect to see from waves Light also constructively and

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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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