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Aim: How can we explain energy transitions in an atom?

Aim: How can we explain energy transitions in an atom?. Do Now: What were the limitations of the Rutherford model of the atom and how did the Bohr model explain these limitations?. Emission Spectra. When electron falls from higher to lower level, photon is emitted.

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Aim: How can we explain energy transitions in an atom?

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  1. Aim: How can we explain energy transitions in an atom? Do Now: What were the limitations of the Rutherford model of the atom and how did the Bohr model explain these limitations?

  2. Emission Spectra • When electron falls from higher to lower level, photon is emitted. • Shows as bright series of lines.

  3. Visible spectrum

  4. Balmer Series • Named after Johann Jacob Balmer 1825-1898

  5. Gas Tube Demo

  6. Energy of photon emitted or absorbed Energy of initial level Energy of final level

  7. Calculate the energy of the photon emitted when a hydrogen atom changes from energy state n = 3 to n= 2, in eV and Joules Ephoton = Ei – Ef Ephoton = -1.51 eV – (-3.40 eV) Ephoton = 1.89 eV 1.89 eV * 1.60 x 10-19 J = 3.0x10-19 J 1 eV

  8. Ephoton = Ei – Ef Ephoton = -5.52 eV – (-10.38 eV) Ephoton = 4.86 eV 4.86 eV * 1.60 x 10-19 J = 7.77 x 10-19 J 1 eV For a mercury electron transition from level c to a, calculate Ephoton, λ, f, and the type of EM wave emitted.

  9. c= fλ 3.00 x 108 m/s = f (2.56 x 10-7 m) f = 1.17 x 1015 Hz This is ultraviolet light Ephoton = hc λ 7.77 x 10-19 J = (6.63x10-34 J•s)(3 x 108 m/s) λ λ = 2.56 x 10-7 m

  10. An electron in a hydrogen atom drops from n = 4, n = 2. Find Ephoton (eV and Joules), f, and the color of light. Ephoton = Ei – Ef Ephoton = -0.85 eV – (-3.40 eV) Ephoton = 2.55 eV 2.55 eV * 1.60 x 10-19 J = 4.08 x 10-19 J 1 eV

  11. Ephoton = hf 4.08 x 10-19 J = (6.63 x 10-34 J•s)f f = 6.15 x 1014 Hz This is blue light

  12. Calculate the energy of the photon needed when a hydrogen atom changes from n =1 to n =∞ Ephoton = Ei – Ef Ephoton = -13.60 eV – 0.00 eV Ephoton = -13.60 eV

  13. Ionization Potential • Minimum energy needed to remove an electron from the ground state to infinity • For hydrogen  -13.6 eV • For mercury  -10.38 eV

  14. A positive photon energy indicated photon is emitted • A negative photon energy indicates photon is absorbed

  15. Absorption Spectra • When electron jumps to a higher energy level a photon is absorbed. • Shows up as a series of dark lines.

  16. Wave Model • After De Broglie proposed matter waves, he was able to show the Bohr model could be explained by considering the orbits of a series of waves

  17. Cloud Model (Shrödinger’s Model) • Quantum mechanics indicates the probability of the electron being in a certain area • Most probable regions are in area called ‘electron cloud’ • Energy levels of Bohr model are divided into sublevels and orbitals -- together with Cloud model define the current model Erwin Shrödinger 1887-1961

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