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Electromagnetic Radiation Electromagnetic Radiation and the Bohr Model of the and the Bohr Model of the
AtomAtomObjective: Students will Objective: Students will
understand the Bohr model of the understand the Bohr model of the atom by understanding light.atom by understanding light.
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Review: Rutherford’s ModelReview: Rutherford’s Model
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Rutherford’s Contributions Rutherford’s Contributions
• 1. He discovered the nucleus
• 2. Found atom to be mostly empty space.
• 3. Knew that the Electrons went around the atom
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Rutherford’s FailureRutherford’s Failure
• He couldn’t explain why the negative electrons aren’t attracted into the positive nucleus, causing the atom to collapse.
http://www.colorado.edu/physics/2000/waves_particles/wavpart2.html
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Neils Bohr
Anyone who isn’t shocked by quantum theory doesn’t understand it.
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What are the components of a What are the components of a wave?wave?
• A wave has frequency and wavelength
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FrequencyFrequency
• The # of peaks that pass by in a given amount of time
• Hz = 1/sec
• MHz = 1,000,000/sec
• KHz = 1,000/sec
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Electromagnetic RadiationElectromagnetic Radiation
Name Several Types of electromagnetic Radiation(325)
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How do waves differ? How do waves differ?
• They have different wavelengths
• They have different frequencies
• They have different energies
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How are they different?How are they different?
• They have different frequencies • They also have different energies
Click here to see how they differ
Then here to see how they are the same!
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What do they all have in common? What do they all have in common?
• They all travel at the speed of light
• 3.00 x 108 meter/sec
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Wavelength and Frequency Wavelength and Frequency
• If the λ = 2 meters and υ = 10/sec, find the speed
• λ x υ = speed
• 2 meters x 10/sec = 20.0 meters/sec
• 5 meters x ______ = 20.0 meters/sec
• So frequency and wavelength are inversely proportional
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KSL Radio’s Wavelength KSL Radio’s Wavelength
• KSL broadcasts at 1160 KHz. Find the λ of KSL’s signal.
• 1160KHz = 1160000 /sec
• Wavelength x frequency = speed
• λ x 1160000 = 3.0 x108 m/sec
(3.0 x108 m/sec)/(1160000/sec) = 258 meters
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What is a PhotonWhat is a Photon
• Photons are light particles. A bundle of energy
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Energy of PhotonsEnergy of Photons
• The energy of a photon is given by this equation E = υ h.
• The symbol “h” represents Planck’s constant. It has a value of
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KSL 1160KSL 1160
• Find the Energy of a photon of light produced by KSL (1160 KHz)
• E = υ h
• E = 1160000 s-1 x 6.626 x 10-34 Js
• E = 7.69 x 10-28 J
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Energy and FrequencyEnergy and Frequency
• How are Energy and υ related?
• The higher the frequency the greater the energy.
• How are Energy and λ related?
• The lower the energy the longer the λ
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Radio WavesRadio Waves
• Turn your book to page 325. What is the electromagnetic with the lowest energy?
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Who or what is Roy G Biv?Who or what is Roy G Biv?
• An acronym for the colors of the rainbow. It is not a person.
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Hydrogen and Roy G BivHydrogen and Roy G Biv
• The colors emitted when energy is passed through hydrogen is
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The Quantum AtomThe Quantum Atom
• Atoms are quantized because they only emit light at certain frequencies and energies.
• A Quantum is the smallest quantity of radiant energy.
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A Staircase Not a RampA Staircase Not a Ramp
• Look at pg 330 Figure 11.15. Like a staircase, the atom has specific energies. A ramp has infinitely small divisions.
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What Does “N” represent?What Does “N” represent?
• The Energy Levels inside the atom
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What values can N haveWhat values can N have
• 1, 2, 3, ….
• In the hydrogen atom, where does the electron reside?
• In the lowest energy level or n=1
• The electron can move up to higher energy levels by absorbing photons.
• We then say the electron is excited
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A relaxing electronA relaxing electron• What happens when an electron relaxes?
• It falls from a high energy level to a lower one.
• What happens to the extra energy?
• It is emitted in the form of light.
• The further an electron falls the more energy it gives off
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What Gives off the Most Energy?What Gives off the Most Energy?
Higher Energy
Lower Energy
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Finding the energy of n=3Finding the energy of n=3
• The equation to find the energy of the hydrogen energy levels is
• E = -2.178 x 10-18 J (1/N2)
• E = -2.178 x 10-18 J (1/32)
• E = -2.42 x 10-19 J
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Finding the difference Finding the difference between n=2 and n=3between n=2 and n=3
• For N=2, E = -5.45 x 10-19 J
• For N=3, E = -2.42 x 10-19 J
• What happens if an electron falls from N=3 to N=2?
• Just take n=2 and subtract n=3, that gives you ΔE
• ΔE = 3.0 x 10-19 J
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Calculate the Calculate the υυ
• E = υ h • 3.03 x 10-19 J = υ h• 3.03 x 10-19 J = υ x 6.626 x 10-34Js• υ = 4.57x 1014 Hz
• λ x υ = 3.03 x 108 meters/sec
• λ x 4.57x 1014 = 3.0 x 108 meters/sec
• λ = 6.56 x 10-7 meters
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The Lyman and Balmer seriesThe Lyman and Balmer series
• If an electron falls to n=1, the energy is to high for us to see.
• It can be detected but it falls into the UV spectrum
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Ultra Violet, Infra Red, VisibleUltra Violet, Infra Red, Visible
• Where the electron falls to determines the type of light it produces.
• If it falls to the n=3, it produces IR.
• We can only se it if it falls to the n=2
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The absorption Spectrum The absorption Spectrum
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Quiz #1 Quiz #1
• 1. What was the shortcoming of the Rutherford model of the atom?
• a. It couldn’t explain how the electron stayed in orbit.
• b. It couldn’t explain the existence of electrons.
• c. It couldn’t explain the existence of protons.
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• 2. Who improved the Rutherford model?
• a. Dalton
• b. JJ Thompsonc. Neils Bohr
• d. Max Plank
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• 3. Who is the constant “h” named after?
• a. Dalton
• b. JJ Thompsonc. Neils Bohr
• d. Max Plank
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• 4. Which has the longest wavelength?
• a. Red Light
• b. UV Lightc. IR Light
• d. Violet Light
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• 5. Which form of electromagnetic energy has the most energy?
• a. Red Light
• b. UV Lightc. IR Light
• d. Violet Light
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• 6. Which element’s spectrum did Bohr explain?
• a. Helium
• b. Hydrogenc. Carbon
• d. Oxygen
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• 7. Which has the lowest energy in the visible spectrum?
• a. Red Light
• b. UV Lightc. IR Light
• d. Violet Light
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• 8. Who found energy levels in the atom?
• a. Dalton
• b. JJ Thompsonc. Neils Bohr
• d. Max Plank
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• 9. W?
• a.
• b. c.
• d.
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• 10. Which electronic transition gives off the most energy in the hydrogen atom?
• a. N2 to N1
• b. N3 to N2c. N4 to N3
• d. N4 to N2