The Quantum Model of the Atom Part 1

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The Quantum Model of the Atom Part 1

• Electrons as Waves

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The Word for the day is

• Quantized-
• Only certain specific values are allowed.
• The electrons energy is quantized. This means
  that it can only have certain specific amounts of
  energy at a given time

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Quantized

• What if the accelerator on your car was
  quantized?
• Is it?

What do you think?
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• Your fingerprint looks like this
• An Elements fingerprint looks like this

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Atomic Emission Spectrum
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• We need someone who could make a connection
  between the atomic emission spectrum of an
  element and the model of an atom
• And his name was
• Bohr
• Neils Bohr

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How did Bohrs model explain the bright line
spectrum produced by hydrogen?

• When the atom absorbs energy the electron jumps
  to a higher energy level (orbit).
• When the electron falls to a lower orbit the
  energy is released as a photon of light.
• Remember a photon is a particle of light
• The color of light produced corresponds to the
  size of the energy change.
• Remember this equation
• E hf

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What type of spectrum is produced when hydrogen
emits light and why?

• A bright line or atomic emission spectrum is
  produced NOT a continuous spectrum
• The electrons energy levels are quantized, the
  energy levels increase by specific certain
  amounts of energy.
• Electrons can only absorb or release certain
  specific amounts of energy. Thus
• only certain specific colors, frequencies or
  photons (energies) of light can be produced!

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• So how did Bohr change the Planetary model
  (Rutherfords model) to make it better?
• Lets take a look!!

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Bohr Model of the Atom
Notice that the electron is changing energy
levels!!
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• How does the photon that is emitted (the released
  energy) correspond to the colored lines we see in
  the atomic emission spectrum?
• Lets look again at Hydrogen

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Remember
Atomic Emission Spectrum Of Hydrogen
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Excited hydrogen atoms emit a pinkish glow.
When the Visible portion of the emitted light is
passed through a prism, it is separated into
specific wavelengths that are part of hydrogens
line-emission spectrum.
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Why are only certain specific colors produced?

• Because the electron can only have certain
  specific amounts of potential energy. In other
  words, it is quantized!
• Thus, the electron can only absorb or release
  certain specific amounts of energycorresponding
  to the specific colors in its atomic emission
  spectrum.

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HOMEWORK

• Pg 118 8,9
• What is the relationship between ROYGBIV and the
  ENERGY CHANGE???

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Quiz class after next
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What did Bohrs Model Give Us

• Three important ideas
• 1 Electrons exist in stable orbits about the
  nucleus
• 2 Only certain orbits are allowed
• 3 An electron must absorb and emit an quantity
  of energy that is equal to the energy change
  between the two levels.

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What were the shortcomings of Bohrs model of the
atom?

• Scientists did not understand why the electron
  could only exist in certain specific orbits or
  energy levels? (quantized)
• It worked perfectly for hydrogen (1 electron) but
  not for the other elements.

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Section 4-2

• The ?????? Model of the Atom

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Matter Waves-The wave-like behavior of
particles (electrons)
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Louis de Broglie

• de Broglie Hypothesis states that any moving
  particle or object has an associated wave.
• For this he won the Nobel Prize in Physics in
  1929
• Tiny electrons behave similar to waves
• When confined to a space, waves can only have
  certain frequencies (energies). Thus, they are
  quantized like electrons in Bohrs model.
• Light has a dual (particle/wave) nature. The
  electron has a dual (particle/wave) nature as
  well.

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Every object has wave properties

• De Broglie wavelength equation
• An electron that has a mass of 9.11 x 10-28 g is
  traveling at 90 mi/hr
• It has a wavelength of 2 x 10-5 m measured in the
  IR section
• A baseball that has a mass of 0.15 kg that is
  pitched at 90 mi/hr
• It has a wavelength of 1.1 x 10-34 m, not
  measurable by any instrument

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Lets take a look at the Double Slit Experiment
http//www.youtube.com/watch?vDfPeprQ7oGc
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Heisenbergs Uncertainty Principle

• It is impossible to determine simultaneously the
  position and velocity of an electron or any other
  particle.
• This is due to the fact that by observing an
  electron, the measurement itself will cause the
  electron to change position. Light will interact
  with an electron and cause it to move.
• The way around this problem is to describe
  electron location in terms of probability of
  finding the electron in certain regions in the
  atom.

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• Werner Heisenberg is speeding down a highway,
  when he's pulled over by the police. The cop
  walks up to him and says, "Excuse me, sir, do you
  know how fast you were driving?"
• Heisenberg looks up to the
• officer and says,
• "Nope, but I know
• exactly where
• I was!"

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SchrÖdingers Wave Equation
Memorize this equation
Just Kidding
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SchrÖdingers Wave Equation

• Equation describes the wave properties of
  electrons and other small particles.
• Proved quantization
• Only waves of specific energies and therefore
  frequencies provide solutions to the equation
• Describes the arrangement of electrons in atoms.

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Together, the ideas that electrons are quantized,
the de Broglie wave properties, the Heisenberg
uncertainty principle and the addition of the
Schrödinger wave equation laid the foundation for
the development of the quantum-mechanical model
of an atom.
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• The modern electron cloud model (a.k.a.
  quantum-mechanical model) shows electrons
  orbiting around the nucleus in specific regions
  (or clouds) based on the probability of finding
  them within that region.

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Yet again another modification to the atomic model

• Lets take a look back

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Homework

• Read pg 98 100
• Answer question 10 on page 118
• Answer question What is the Heisenberg
  Uncertainty Principle??

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Orbitals

• ORBITAL ? ORBIT
• A three dimensional region around the nucleus
  that indicates the most probable location of an
  electron with a given energy.
• Higher probability higher electron density
• Lower probability lower electron density
• There are several different types of orbitals
  each having a different fundamental shape.

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The 5 d orbitals
http//www.winter.group.shef.ac.uk/orbitron/AOs/3d
/index.html
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Homework

• Read pg. 101-104
• Questions 1-3 on pg 104