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Exploring the Wave-Particle Duality in Chemistry

Learn about subatomic particles, electromagnetic waves, quantum theory, and the dual nature of light and matter in chemistry. Understand atoms, photons, emission spectra, and the Bohr atom model. Explore Heisenberg's Uncertainty Principle.

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Exploring the Wave-Particle Duality in Chemistry

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  1. CHEMISTRY 161 Chapter 7

  2. 1. Structure of an Atom subatomic particles electrons neutrons protons

  3. 17e 17p 18n 35 17 Cl mass number 18 neutrons atomic number Why are atoms stable? e- classical physics predicts that electron falls into nucleus

  4. 2. Waves

  5. wavelength [m] . . amplitude l direction of propagation Intensity distance, x EXP1 v = x/t t = x/v

  6. . . period [s] T direction of propagation Intensity time, t [1 Hz = 1 s-1] Hertz Frequency [s-1]

  7. Frequency and Wavelength wavelength frequency speed of radiation m s-1 meter (m) Hz or s-1 LONG WAVELENGTH, LOW FREQUENCY

  8. light can be described as a wave

  9. POSTULATE visible light consist of electromagnetic waves speed of propagation (speed of light) c = 3  108 ms-1 James Maxwell

  10. light has two components • electric field • magnetic field

  11. ELECTROMAGNETIC SPECTRUM INCREASING FREQUENCY & ENERGY EXP2

  12. VISIBLE SPECTRUM Wavelength l (nanometers) ln = c Which color has the higher frequency? 1 = orange 2 = blue

  13. The wavelength of the yellow light from a lamp is 589 nm. What is the frequency of the radiation?

  14. 3. Postulates Na K Li different atoms emit distinct light EXP3

  15. h is Planck’s constant h = 6.626 x 10-34 J s Max Planck

  16. energy can be emitted or absorbed only in discrete quantities (little packages) EXP4/5

  17. Emission Nebula

  18. CLASSICAL any amount of energy can be emitted or absorbed NON-CLASSICAL energy can be emitted or absorbed only in discrete quantities (little packages) energy is not continuous QUANTUM smallest amount of energy which can be absorbed/ emitted

  19. 3. Properties of Photons POSTULATE Electromagnetic radiation can be viewed as a stream of particle-like units called photons Albert Einstein

  20. ABSORPTION OF A PHOTON Efinal atoms and molecules absorb discrete photons (light quanta) Einitial EXP6

  21. Duality of Wave and Corpuscle light has properties of a wave and of a particle de Broglie

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

  23. 4. Properties of Electrons de Broglie wavelength each particle can be described as a wave with a wavelength λ

  24. WAVE-PARTICLE DUALITY matter and light (photons) show particle and wave-like properties MASS INCREASES WAVELENGTH GETS SHORTER WAVELENGTH GETS LONGER MASS DECREASES

  25. WAVE-PARTICLE DUALITY large pieces of matter are mainly particle-like small pieces of matter are mainly wave-like MASS Baseball Proton Electron Photon Particle-like Wave-like

  26. 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)

  27. 5. Electrons, Photons, Atoms EMISSION OF A PHOTON atoms and molecules emit discrete photons Einitial electrons in atoms and molecules have discrete energies Efinal

  28. EMISSION SPECTRA analyze the wavelengths of the light emitted only certain wavelengths observed only certain energies are allowed in the hydrogen atom

  29. Balmer found that these lines have frequencies related n = 1, 2, 3, 4, 5…

  30. 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……...

  31. 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

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

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

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

  35. Ephoton = h BOHR ATOM ENERGY LEVEL DIAGRAM En n=4 n=3 -A/9 -A/4 n=2 ENERGY e- n=1 -A ELECTRON EXCITATION

  36. 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

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

  38. ABSORPTION OF A PHOTON nf ni

  39. ABSORPTION OF A PHOTON nf ni

  40. ABSORPTION OF A PHOTON nf energy is absorbed ni

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

  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. THE BOHR ATOM QUANTUM NUMBERS n = 4 n = 3 n = 2 n = 1 absorption emission e- ionization energy

  45. 6. HEISENBERG’S UNCERTAINTY PRINCIPLE in the microscopic world you cannot determine the momentum (velocity) and location of a particle simultaneously Dx is the uncertainty in the particle’s position Dp is the uncertainty in the particle’s momentum EXPVII

  46. THE HEISENBERG UNCERTAINTY PRINCIPLE if particle is big then uncertainty small

  47. This means we have no idea of the velocity of an electron if we try to tie it down! Alternatively if we pin down velocity we have no idea where the electron is! So for electrons we cannot know precisely where they are!

  48. we cannot know precisely where electrons are! we cannot describe the electron as following a known path such as a circular orbit Bohr’s model is therefore fundamentally incorrect in its description of how the electron behaves.

  49. Schroedinger (1926) Born (1927)

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