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CHEMISTRY 161 Chapter 7 Quantum Theory and Electronic Structure of the Atom

CHEMISTRY 161 Chapter 7 Quantum Theory and Electronic Structure of the Atom www.chem.hawaii.edu/Bil301/welcome.html. REVISION. 1. light can be described as a waves of a wavelength and frequency. 2. light can be emitted or absorbed only in discrete quantities (quantum – package - photon).

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CHEMISTRY 161 Chapter 7 Quantum Theory and Electronic Structure of the Atom

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  1. CHEMISTRY 161 Chapter 7 Quantum Theory and Electronic Structure of the Atom www.chem.hawaii.edu/Bil301/welcome.html

  2. REVISION • 1. light can be described as a waves of a • wavelength and frequency 2. light can be emitted or absorbed only in discrete quantities (quantum – package - photon) 3. duality of wave and corpuscle

  3. 2. Properties of Electrons Deflection of Cathode Rays anode (+) fluorescent screen cathode (-) focus anode (+) particles are negatively charged; particles are defined as ‘electrons’

  4. de Broglie wavelength each particle can be described as a wave with a wavelength λ (interferences)

  5. out of phase wave add destructive interference

  6. add in phase wave constructive interference

  7. q electrometer electron gun gold foil current angle (q) interference patterns

  8. Diffraction of an electron beam (metal crystal) WAVE-PARTICLE DUALITY

  9. WAVE-PARTICLE DUALITY matter and energy show particle and wave-like properties MASS INCREASES WAVELENGTH GETS SHORTER WAVELENGTH GETS LONGER MASS DECREASES

  10. What are the wavelengths of a 0.10 kg ball moving at 35 m/s and an electron moving at 1.0 x 107 m/s? Solution: h = 6.626 x 10-34 J s 1J = kg m2 s-2 Ball: l = 1.9 x 10-34 m

  11. What are the wavelengths of a 0.10 kg ball moving at 35 m/s and an electron moving at 1.0 x 107 m/s? Solution: h = 6.626 x 10-34 J s 1J=kg m2 s-2 Electron: l = 7.3 x 10-11 m

  12. What are the wavelengths of a 0.10 kg ball moving at 35 m/s and an electron moving at 1.0 x 107 m/s? Solution: h = 6.626 x 10-34 J s 1J=kg m2 s-2 Ball: l = 1.9 x 10-34 m Electron: l = 7.3 x 10-11 m massive particles have immeasureably small wavelengths

  13. WAVE-PARTICLE DUALITY large pieces of matter are mainly particle-like, with very short wavelengths small pieces of matter are mainly wave-like with longer wavelengths MASS Baseball Proton Electron Photon Particle-like Wave-like

  14. 1. light behaves like wave and particle 2. electron behaves like wave and particle 3. electrons are constituents of atoms 4. light is emitted/absorbed from atoms in discrete quantities (quanta)

  15. EMISSION OF A PHOTON atoms and molecules emit discrete photons Einitial electrons in atoms and molecules have discrete energies Efinal

  16. EMISSION SPECTRA white light passing through a prism gives a continuous spectrum

  17. HYDROGEN DISCHARGE we can analyze the wavelengths of the light emitted

  18. EMISSION SPECTRA analyze the wavelengths of the light emitted only certain wavelengths observed

  19. white light (continuous spectrum) hydrogen gas (line spectrum) experimental evidence only certain energies are allowed in the hydrogen atom

  20. CHARACTERISTIC LINE SPECTRUM OF HYDROGEN n=4 n=5 n=3 Balmer found that these lines have frequencies related

  21. THE BOHR ATOM Niels Bohr

  22. THE BOHR ATOM e- electrons move around the nucleus in only certain allowed circular orbits

  23. THE BOHR ATOM electrons move around the nucleus in only certain allowed circular orbits as long as an electron remains in a given orbit its energy remains constant and no light is emitted e- Bohr’s postulate

  24. WHY THE ELECTRON DOES NOT CRASH INTO THE NUCLEUS? Bohr postulated that the wavelength of the electron just fits the radius of the orbit. three wavelengths STABLE

  25. WHY THE ELECTRON DOES NOT CRASH INTO THE NUCLEUS? five wavelengths STABLE

  26. THE BOHR ATOM electrons move around the nucleus in only certain allowed circular orbits QUANTUM NUMBERS n = 4 n = 3 n = 2 n = 1 each orbit has a quantum number associated with it e- n is a QUANTUM NUMBER n= 1,2,3,4……...

  27. THE BOHR ATOM QUANTUM NUMBERS and the ENERGY n = 4 n = 3 n = 2 n = 1 Z = atomic number of atom A = 2.178 x 10-18 J = Ry THIS ONLY APPLIES TO ONE ELECTRON ATOMS OR IONS

  28. BOHR ATOM ENERGY LEVEL DIAGRAM HYDROGEN ATOM! Z=1

  29. BOHR ATOM ENERGY LEVEL DIAGRAM En ENERGY n=1 -A

  30. BOHR ATOM ENERGY LEVEL DIAGRAM En -A/4 n=2 ENERGY n=1 -A

  31. BOHR ATOM ENERGY LEVEL DIAGRAM En n=4 n=3 -A/9 -A/4 n=2 ENERGY n=1 -A

  32. En -A/16 n=4 0 n=3 -A/9 -A/4 n=2 Energy e- n=1 -A

  33. En -A/16 n=4 0 n=3 e- -A/9 -A/4 n=2 excite electron to a higher energy level Energy ELECTRON EXCITATION n=1 -A

  34. Ephoton = h En to excite the electron we need energy n=4 0 n=3 -A/9 this can be in the form of a photon -A/4 n=2 Energy e- n=1 -A

  35. ELECTRON DE-EXCITATION En n=4 0 n=3 -A/9 -A/4 e- n=2 emission of energy as a photon Energy e- n=1 -A

  36. ABSORPTION OF A PHOTON nf only a photon of the correct energy will do ni

  37. ABSORPTION OF A PHOTON nf ni

  38. ABSORPTION OF A PHOTON nf ni

  39. ABSORPTION OF A PHOTON nf This means energy is absorbed! ni

  40. EMISSION OF A PHOTON ni nf This means energy is emitted!

  41. n = Ion ... 8 } n = 4 Excited states n = 3 n = 2 Energy n = 1 Ground state hydrogen emission spectrum For the Lyman series, nf= 1 and ni = 2,3,4… For the Balmer series, nf = 2 and ni = 3,4,5… For the Paschen series, nf = 3 and ni = 4,5,6…

  42. IONIZATION OF AN ATOM nf ni This means energy is absorbed!

  43. IONIZATION ENERGY DE = 2.178 x 10-18 J for one atom the ionization energy for one mole is = 2.178x 10-18 J atom-1 x 6.022x1023 atoms mol-1 =13.12 x 105 J mol-1 = 1312 kJ mol-1

  44. WAVELENGTH OF PHOTON H+ + e– H IE = 2.178 x 10-18 J for one H atom

  45. SUMMARY THE BOHR ATOM QUANTUM NUMBERS n = 4 n = 3 n = 2 n = 1 e- Z = atomic number of atom A = 2.178 x 10-18 J = Ry

  46. Homework Chapter 7, pages 252-263 problems

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