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Quantum Mechanics

Quantum Mechanics

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Quantum Mechanics

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  1. Quantum Mechanics Chapters 4 & 5

  2. WAY WAY BACK IN TIME... • Greek philosopher Democritus (460-370 BCE.) • substances that comprised nature • empty space • tiny particles • “atoms”

  3. Democritus • different kinds of atoms existed • not able to be broken down by ordinary means

  4. Aristotle • More popular • a contemporary of Democritus • matter was a continuous substance which he called "hyle“ • this idea was accepted without support for nearly two thousand years.

  5. pseudo- science • explained natural phenomena in philosophical ways • without experimentation • without logic • maggots come from rotting meat • frogs cause warts

  6. Isaac Newton, Robert Boyle and John Dalton • Questioned natural occurrences • conducted experiments • controlled variables • made observations • collected data • data and observations used to support hypotheses

  7. John Dalton • matter is particulate in nature • atoms of a single element are identical • atoms of different elements are different from each other • Dalton's hypothesis explained the observations • first modern atomic theory

  8. J.J. Thomson • Are atoms really the smallest particles? • Cathode ray tubes • Rays originated at the cathode (negative electrode) and traveled toward the anode (positive electrode). • Produced rays composed of negatively charged subatomic particles • he called particles electrons (e-). • mathematically calculated the electron's mass to charge ratio

  9. Oil Drop Experiment • Robert Millikan • determined the charge of a single electron (-1) • Oil Drop Experiment

  10. Thomson Atom • Plum Pudding Model • Electrons

  11. Atomic Research • Ernest Rutherford • Niels Bohr • Hans Geiger • Ernest Marsden • Experiment to study structure of atom • Gold Foil Experiment

  12. Gold Foil Experiment • Ernest Rutherford • positively charged helium nuclei (alpha () particles) propelled at high speed toward a thin sheet (tissue paper-like) of gold foil surrounded by a fluorescent screen

  13. Experimental Results: • 1. Most of particles pass straight through foil • 2. Some particles are slightly deflected • 3. A few particles (1 per 8000) are deflected greatly. Nearly bounce back to origin.

  14. Conclusions based on experimental data: • 1. The atom is mostly space. • 2. Mild deflection was caused by repulsion of similar electrostatic charge. Therefore, the atom has a positive region. 'Protons“ • 3. The positive core is very small (1 x 10-12 of total atomic volume) and contains most of the atom's mass. 'Nucleus'

  15. Rutherford Atom

  16. The Atom is mostly empty space…..

  17. Eugene Goldstein • showed that protons created rays in a cathode ray tube just as the electrons had done • traveled in the opposite direction. (anode to cathode) • concluded that a proton is equal but opposite in charge to the electron, or 1+, and approximately 1836 times more massive

  18. Thomson's observation • Atoms that are • chemically identical can have variable mass

  19. James Chadwick • credited with the discovery of the neutral subatomic particle - the neutron • Walter Bothe obtained initial evidence nearly two years before Chadwick's experiments • Neutrons have a mass nearly identical to that of the proton, but no electrical charge.

  20. Explanation lies with the neutrons • Isotopes • Atoms of the same element containing different numbers of neutrons. • Nuclide • a particular isotope • Each isotope acts the same in chemical reaction • Each nuclide will produce a product of different mass.

  21. Proton + Neutron Electron - Deuterium 1 proton, 1 electron, 1 neutron Protium 1 proton, 1 electron Hydrogen isotopes Tritium 1 proton, 1 electron, 2 neutrons

  22. TO SUMMARIZE... • The atom is the smallest particle of matter that cannot be chemically subdivided. • Composed of two regions and three primary subatomic particles. • Nucleus • very small • positively charged • dense. • Protons • Neutrons • Electron Cloud • Electrons • orbit the nucleus. • Small point-like negative charges

  23. IN PERFECT BALANCE • The atom is electrically neutral • contain equal number of: • protons (positive charges) and • electrons (negative charges).

  24. Remind you of anything?

  25. Niels Bohr • 1913 • Introduced ‘Planetary Model’

  26. Planetary Model • Gravity and Inertia

  27. Attractive force: Gravity Pulls planet toward sun Repulsive force: Inertia Pushes planet in a straight line away from sun Attractive force: + / - charges + nucleus pulls – electrons toward it Repulsive force: Solar SystemAtom

  28. It Ought to Go SPLAT! • “A charged particle constrained to move in curved path … radiates energy according to Maxwell equations.” Some basic principles of synchrotron radiation. (document prepared by Antonio Juarez-Reyes, AMLM group, 2001) • Electrons – constant orbit • Energy drain • and the atom goes SPLAT!

  29. Electromagnetic Radiation

  30. Electromagnetic Radiation • c = 3.0 X 108 m/s Wavelength =λ Frequency = f (υ)

  31. Louis de Broglie Dual Nature of Light Wave Nature Travels through space in waves Travels at speed of light (c) Particle Nature Interacts with matter as a particle Quanta (unit of energy) transferred to matter in packets of light (photons) Electromagnetic Radiation

  32. Electromagnetic Radiation Light →

  33. Electromagnetic Radiation Light → Excited atomic state

  34. Electromagnetic Radiation e- jumps to Higher Energy level Light → Excited atomic state

  35. Electromagnetic Radiation e- jumps to e- jumps to Higher Energy Lower Energy level level Light → Excited atomic →→→→→→ state

  36. Electromagnetic Radiation e- jumps to e- jumps to Higher Energy Lower Energy level level Light → Excited atomic →→→→→→ state

  37. Electromagnetic Radiation e- jumps to e- jumps to Higher Energy Lower Energy level level Light →Excited atomic →→→→→→ Atom in Ground State state photon released

  38. Electromagnetic Radiation e- jumps to e- jumps to Higher Energy Lower Energy level level Light →Excited atomic →→→→→→ Atom in Ground State state photon released Bright-line Spectrum

  39. Speed of wave c=fλ solving for frequency c=f λ c= λ ch= E= Energy of photon E=hf solving for frequency E=f h E h Eλ ch λ Electromagnetic Radiation

  40. Electromagnetic Radiation • Irwin Schrodinger • Developed the ‘Wave Equation’ • to support de Broglie’s idea of the dual nature of light

  41. Quantum Leap • Bohr’s Planetary Model is used to explain the spectral lines produced by atoms. • Quantum leap animation

  42. Quantum Leap • The color of light indicates its wavelength • A particular wavelength has a definite frequency • A particular wavelength has a definite amount ofenergy

  43. Riding the Wave (Equation) • The Wave Equation • confirmed Bohr’s theory of quantized energy levels. • Treating electrons as waves, explains why the tiny negative electrons are not drawn into the more massive and positive nucleus

  44. Riding the Wave • “A charged particle constrained to move in curved path … radiates energy according to Maxwell equations.” Some basic principles of synchrotron radiation. (document prepared by Antonio Juarez-Reyes, AMLM group, 2001) • As the e- approach the • nucleus, their wavelengths • become shorter. • E = ch • λ

  45. Attractive force: Gravity Pulls planet toward sun Repulsive force: Inertia Pushes planet in a straight line away from sun Attractive force: + / - charges + nucleus pulls – electrons toward it Repulsive force: Energy produced form the shorter λ pushes the e- away from the nucleus Solar SystemAtom

  46. QUANTUM MECHANICS • Electrons do not obey the laws of classical or Newtonian physics • A new science to describe the laws of small particles was established

  47. LOOK! IT ISN'T THERE! • Uncertainty principle • Not possible to locate an electron's exact position • Position and momentum cannot be determined at the same time • to determine one you effect a change in the other • Electrons - only "seen” when they jump from a higher to lower energy level. • once electron is "seen," its direction and speed are different from what they were prior to observation. • Determining position changes its momentum. • Applies to electron when it is considered a particle Werner Heisenberg

  48. WAVE REVIEWS! • Irwin Schrodinger • Wave equation • helps locate probable regions of electron population if considered it to be like a wave. • general paths of the electrons around the nucleus can be determined