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Quantum Chemistry

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Title: Quantum Chemistry


1
Quantum Chemistry
  • AP Chemistry Unit 7

2
Electromagnetic Radiation
  • Electromagnetic radiation Energy that travels at
    the speed of light and has wavelike behavior
  • Waves
  • Wavelength, ? in meters
  • Frequency, ? in cycles per sec, 1/s, s-1 or
    Hertz (Hz)
  • Speed, c 2.9979 x 108 m/s

3
Waves
  • The distance between corresponding points on
    adjacent waves is the wavelength (?).
  • The height of the wave is amplitude.

4
Waves
  • The number of waves passing a given point per
    unit of time is the frequency (?).
  • For waves traveling at the same velocity, the
    longer the wavelength, the smaller the frequency.

5
Electromagnetic Radiation
  • All electromagnetic radiation travels at the same
    velocity the speed of light (c), 3.00 ? 108
    m/s.
  • Therefore,
  • c ??

6
The Nature of Energy
  • The wave nature of light does not explain how an
    object can glow when its temperature increases.
  • Max Planck explained it by assuming that energy
    comes in packets called quanta.

7
The Nature of Energy
  • Einstein used this assumption to explain the
    photoelectric effect.
  • He concluded that energy is proportional to
    frequency
  • E h?
  • where h is Plancks constant, 6.63 ? 10-34 J-s.
  • Suggested EM radiation is stream of particles
    photonsenergy has mass!
  • E mc2

8
The Nature of Energy
  • Therefore, if one knows the wavelength of light,
    one can calculate the energy in one photon, or
    packet, of that light
  • c ??
  • E h?

9
The Nature of Energy
  • Another mystery involved the emission spectra
    observed from energy emitted by atoms and
    molecules.

10
The Nature of Energy
  • One does not observe a continuous spectrum, as
    one gets from a white light source.
  • Only a line spectrum of discrete wavelengths is
    observed.

11
The Nature of Energy
  • Niels Bohr adopted Plancks assumption and
    explained these phenomena in this way
  • Electrons in an atom can only occupy certain
    orbits (corresponding to certain energies).

12
The Nature of Energy
  • Niels Bohr adopted Plancks assumption and
    explained these phenomena in this way
  • Electrons in permitted orbits have specific,
    allowed energies these energies will not be
    radiated from the atom.

13
The Nature of Energy
  • Niels Bohr adopted Plancks assumption and
    explained these phenomena in this way
  • Energy is only absorbed or emitted in such a way
    as to move an electron from one allowed energy
    state to another the energy is defined by
  • E h?

14
The Nature of Energy
  • The energy absorbed or emitted from the process
    of electron promotion or demotion can be
    calculated by the equation

where RH is the Rydberg constant, 2.18 ? 10-18 J,
and ni and nf are the initial and final energy
levels of the electron.
15
The Wave Nature of Matter
  • Louis de Broglie posited that if light can have
    material properties, matter should exhibit wave
    properties.
  • He demonstrated that the relationship between
    mass and wavelength was

16
Dual Nature of Light
  • Wave properties
  • Particulate properties
  • Small bits of matter like photons exhibit mostly
    wave properties because mass is negligible.
  • Medium bits of matter like electrons exhibit
    particulate and wave properties
  • Large pieces of matter like you exhibit
    particulate behavior, waves are so small, not
    observed.

17
Nature of Energy
  • Bohr atom model only worked with hydrogen its 1
    electron
  • Physics says a charged particle accelerating
    (orbit) emits energy
  • Would lose energy crash into nucleus?

18
Energy Levels of Atoms
  • An excited e- that returns to the ground state
    releases energy in the form of light.
  • Review H2 Lab from regular chem!

19
Light Series
20
Rydberg Equation
  • Calculating the energy released as an electron
    moves energy levels
  • E -2.178 x 10-18J (Z2)
  • ( n2)

Nuclear charge
Energy level 1,2,3
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