1 / 79

Quantum Mechanics

Quantum Mechanics. Chapters 4 & 5. WAY WAY BACK IN TIME. Greek philosopher Democritus (460-370 BCE.) substances that comprised nature empty space tiny particles “atoms”. Democritus. different kinds of atoms existed not able to be broken down by ordinary means. Aristotle.

azizi
Télécharger la présentation

Quantum Mechanics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related