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ENERGY & LIGHT

ENERGY & LIGHT. THE QUANTUM MECHANICAL MODEL. Atomic Models. What was Dalton’s model of the atom like ? Thomson’s? Rutherford’s? What is the significance of the proton? What is the significance of the electron?

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ENERGY & LIGHT

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  1. ENERGY & LIGHT THE QUANTUM MECHANICAL MODEL

  2. Atomic Models • What was Dalton’s model of the atom like? • Thomson’s? Rutherford’s? • What is the significance of the proton? • What is the significance of the electron? • To understand the quantum mechanical model of the atom, we need an understanding of light and how it transmits energy.

  3. Energy is transmitted in waves by radiation • What are different kinds of radiation? • Visible light, microwaves, x-rays • What is the electromagnetic spectrum? • The whole range of types of radiation. • What is meant by the “dual nature” of light? • Light behaves as waves. • Light behaves as packets of energy called photons.

  4. Anatomy of a Wave • Crest • Trough • Amplitude • Frequency

  5. Electromagnetic Spectrum • All waves of EMS travel at the speed of light in a vacuum • Speed of light = 3.00 X 108 m/s • C = λνλ = wavelength ν = frequency in m or cm in Hz or s-1

  6. Problem 1 • What is the frequency of a wave if the wavelength is 5.00 X 10-6 m? • Look on page 362. What part of the EMS is it in?

  7. Problems 2 & 3 • What is the wavelength of radiation if the frequency is 1.5 X 1013 Hz? • Is it longer or shorter than red light waves? • What is the wavelength of yellow light emitted by sodium vapor lamp if the frequency is 5.10 X 1014 Hz

  8. Waves & Energies Max Planck • Different wavelengths have different energies • Planck explains why metals change colors when heated with the mathematical expression Eq = hν • Planck’s constant h = 6.626 X 10-34J.s • Energy of a body changes in small discrete units (quanta) – like bricks of a wall • Quantum – amount of energy to move an electron up one energy level

  9. Waves & Energies Albert Einstein • Proposed that light could be described as quanta of energy called photons (bundles of energy) • This explained the photoelectric effect – certain energy levels will excite e- of metals and others will not. • Revised equation – Ep= hν

  10. Problems 4 & 5 • Calculate the energy of a quantum of radiant energy with a frequency of 5.00 X 1015 Hz? • What is the energy of a photon of microwave radiation with a frequency of 3.20 X 1011s-1?

  11. Atomic Emission Spectra • Bohr applied quantum theory to explain AES of hydrogen. • Ground state – lowest possible energy level of an electron • If an electron moves up energy level(s) it is quantized. • If it falls back down, emits same amount of energy in the form of visible light (photons)

  12. Atomic Emission Spectra • Color of light emitted is unique to element • How astronomers determine composition of stars. • Is a discontinuous spectrum as opposed to continuous (light through a prism)

  13. Atomic Emission Spectra • Bohr’s theory didn’t explain for all atoms • New ideas – deBroglie’ s mathematical model λ = h/mvwhere λ = wave length, h= Planck’s constant, m = mass, and v = velocity • Visible objects produce wavelengths too small to be seen or easily measured – 200g baseball traveling at 30 m/s has λ of 1X 10-32cm • Electrons by contrast have λ large enough to be measured – 2 X 10-3 cm

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