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Quantum Mechanics Presentation Quantum Mechanics Presentation Presentation Transcript

  • Quantum Mechanics Parima Shah and Jasmine Wang (In less than 20 minutes)
  • Quantum Mechanics? Well, not anymore Ugh.
  • What is Quantum Mechanics? It’s a new way of looking at the atomic world and understanding our universe. In order to understand chemistry and science, we must start at the fundamentals of physics.
    • We’ll cover
      • Orbitals and shells (an overview)
      • Light (Waves and Particles)
      • Electromagnetic Spectrum
      • Photoelectric Effect
      • Line Spectra
      • The Atom
    View slide
  • Orbitals and Shells: A Quick Review
    • Pauli Exclusion : no two electrons have the same four quantum numbers
    • Aufbau : “ building up ”
    • Hund’s : electrons occupy separate orbitals and share the same spin , pairing up only after all the orbitals are full
    • Quantum Numbers
      • Principal ( n )
        • Shell
        • Integers
      • Angular momentum ( l )
        • Subshell
          • [ 0, n-1 ]
      • Magnetic ( m l )
        • Orbital
        • [ -l, +l ]
      • Spin ( m s )
        • 2 electrons
        • +/- ½
    Paramagnetic: unpaired electrons Diamagnetic: paired electrons View slide
  • The Nature of Light
    • Newton thought that light behaved like particles while Christian Huygens believed it behaved like waves.
    • Waves:
      • A pattern of matter, energy, or both
      • Waves, unlike particles can be spread out over an immense area
      • Frequency is the amount of times the wavelength occurs
    • Particles:
      • A particle is a discrete object.
      • Occupies a single, localized volume of space
      • All energy is concentrated in that space
      • One can tell where it is and how it is moving
  • The anatomy of a Wavelength
  • Light as Electromagnetic Waves
    • Visible light
      • narrow bands of frequencies
    • Light has a larger spectrum of electromagnetic waves
      • All electromagnetic waves travel at the same speed: 300,000,000 m/s
    • Can move through a vacuum
    Did you Know? It was believed that light had to travel through ether (water moved through waves and sound moved through air)
  • Let’s see if this recipe actually works… Banana Bread Cheese Cake: Strawberry Wavelength & Frequency are related c= νλ c =3.00 x 10 8 m/s ν = frequency in /s λ = wavelength in m Frequency and wavelength formula
  • Time to cook: Solution: λ =c/ υ What is the wavelength of a yellow sodium emission of frequency 5.09 x 10 -7 /s? = 5.89 x 10 14 m
  • The Blackbody Problem
    • A blackbody cannot be built, but it can be approximated by using an empty box containing electromagnetic energy.
        • Energy must be at equilibrium between walls and interior 
        • Waves must fit inside the box
        • The lowest possible frequency of light has a wavelength that fits the box exactly.
        • Each consecutive frequency fits into the box depending on its wavelength (the next would be two wavelengths, &c. to infinity)
        • At infinity, there is an infinite amount of energy because each wave carries energy
        • Led to discovery of UV light
    Emits all possible radiation Absorbs all possible radiation
  • Max Planck and the beginnings of Quantum Mechanics
    • Max Planck: Each quanta must have a minimum of energy that is some proportion of the overall energy of the system
    POUCH
      • 25¢
    Quanta of my money is falling out!
  • Max Planck and the beginnings of Quantum Mechanics POUCH
      • radiation could be absorbed/emitted in small amounts called quanta – packets of energy
          • Multiplied by a conversion factor ( Planck’s constant ( h ) = 6.6 x 10 -34 )
          • An atom at a particular frequency ν could emit energy only in integer multiples of h ν , but nothing less than 1 h ν .
  • Lenard’s Photoelectric Experiments: Paradise. (not really)
  • Lenard’s Photoelectric Experiments: Paradise. (still not really)
    • Philip Lenard
    • The greater the intensity of incoming light, the greater number of electrons released
    • Example: Waves on the Beach
    • Bigger waves dislodge more sand than weak waves
  • Lenard’s Photoelectric Experiments: Paradise. (not getting realer) The kinetic energy in each “escaping” electron does not increase with intensity. In other words, intensity does not matter on the speed of the electrons. More and more sand was being dislodged, but no more violently than the weaker waves
  • Does this make sense in the world of physics? Does that make sense for waves? Lenard’s Photoelectric Experiments: Paradise. (nope) Does this make sense in the world of physics? Does this make sense in the world?
  • NO! Nada, Goose egg, a cookie, etc. etc.
  • So what?
    • Light must not only work as waves, but as quanta of energy, or particles
    Then he discovered: Increasing the intensity of the light did not increase the kinetic energy of the escaping electron ejection. (Remember: waves on the beach example) However, the frequency did. What does that mean? Light is a stream of quanta instead of being a continuous wave. Electrons are ejected because quanta hit them – the quanta transfers all its energy to the electron. This means…
  • The Photoelectric Effect The ejection of electrons from the surface of a metal from another material when light shines on it. Einstein adapted Planck’s quanta theory Photons- Quanta of light E= h ν where E is energy and h is Planck's constant of The amount of energy of each photon is miniscule. Light on sodium metal in vacuum Electrons ejected from the surface SODIUM METAL
  • Emission Line Spectra
    • Continuous Spectrum - all wavelengths
    • Line spectrum - only specific wavelengths
  • Bohr’s Theory of the Hydrogen Atom Energy Level Postulate : electrons can have only specific energy values in an atom, called energy levels. Bohr’s rule for the quantization of a electron in the hydrogen atom :
  • Transitions between Energy Levels : An electron can change energy by transferring one energy level to another energy level. The emission of light from the atom occurs when the electron in a higher energy level moves to a lower energy level. The electron loses energy, which is emitted as a photon. Bohr’s Theory of the Hydrogen Atom
  • Example Problem
    • What is the wavelength of light emitted when the electron in a hydrogen atom undergoes transition from energy level n=4 to n=2?
  • Solution to Example Problem
    • The CD Player: Energy Levels and the good old days
  • Flame Test (demo)
    • Materials
    • 0.50M solution Copper Chloride (CuCl 2 )
    • 0.50M solution Lithium Chloride (LiCl)
    • Tyrrell Burner
    • 0.50M solution Sodium Chloride (NaCl)
    • 0.50M solution Potassium Chloride (KCl)
    • 4 wood splints
    • 4 beakers
  • Flame Test (demo)
    • WEAR SAFETY GOGGLES
    • Tie up hair and loose clothing when using flame
    • Use care with Tyrrell burners and the flame
    Safety Precautions
  • Flame Test (demo)
    • Procedure
    • Saturate a wood splint in each 0.50 solution of metal
    • Take splint from the NaCl solution and place in hottest part of the flame
    • Observe and record the color
    • Repeat for LiCl, CuCl 2 , KCl
  • Flame Test (demo)
    • Flame Colors
    K Cu Li Na Potassium Copper Lithium Sodium Element Purple Green Crimson Yellow Color
  • Flame Test (demo)
    • The colors seen in the flame from each substance are a demonstration of the excitement of electrons from each element from their energy levels in order to emit photons.
    Why does this relate?
  • Works Cited
    • http://www.answers.com
    • http:// www.hi.is/~hj/QuantumMechanics/quantum.html
    • http://www.800mainstreet.com/spect/emission-flame-exp.html
    • http://xmm.sonoma.edu/edu/lessons/activity-flame.html
    • http://www.kent.k12.wa.us/staff/carriewattles/chemistry/flametestlab_inst.htm
    • http://www.creative-chemistry.org.uk/activities/documents/flametests.pdf
    • http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
    • How mathematical models, computer simulations, and exploration can be used to study the universe : an anthology of current thought / edited by Fannie Huang. 1st ed. New York : Rosen Pub. Group, 2006.
    • Bynum, Wf, Ej Browne, and Roy Porter, eds. "Quantum." Dictionary of the History of Science . 1st ed. 1 vols. Princeton: Princeton UP, 1981.
    • Willett, Edward. The Basics of Quantum Physics: Understanding the Photoelectric Effect and Line Spectra . 1st ed. Vol. 1. New York: The Rosen Group, Inc., 2005. 6-19, 30-43.