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Electromagnetic%20Radiation

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Each element has a unique pattern. Bohr (1913). The hydrogen e-: Orbits the nucleus. ... Electromagnetic Radiation Author: Vining Last modified by: odagomo – PowerPoint PPT presentation

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Title: Electromagnetic%20Radiation


1
  • BUSINESS
  • EXAM 2 THURSDAY NOVEMBER 4, 2010
  • MATERIAL COVERED CHAPTERS 4, 5 6
  • TIME 700PM-800PM
  • WHERE (TO BE ANNOUNCED LATER)
  • WHAT TO BRING CALCULATOR, ONE PAGE OWN
    NOTES
  • CONFLICT IN SCHEDULE? CONTACT ME TO MAKE SEPARATE
    TIME

2
Chapter 6 Electromagnetic Radiation
3
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4
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5
Short wavelength --gt high frequency high
energy
  • Long wavelength --gt
  • small frequency
  • low energy

6
The electromagnetic spectrum.
7
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8
Which has the longest wavelength?
  1. Infrared
  2. Ultraviolet
  3. X-rays
  4. Radio waves

9
  • Rank the following in order of increasing
    frequency
  •  
  • microwaves
  • radiowaves
  • X-rays
  • blue light
  • red light
  • UV light
  • IR light

10
  • Waves have a frequency
  • Use the Greek letter nu, ?, for frequency, and
    units are cycles per sec
  • All radiation ? ? c
  • c velocity of light 3.00 x 108 m/sec
  • Long wavelength ?small frequency
  • Short wavelength ?high frequency

11
The Wave Nature of Light
  • The product of the frequency, n (waves/sec) and
    the wavelength, l (m/wave) would give the speed
    of the wave in m/s.
  • So, given the frequency of light, its wavelength
    can be calculated, or vice versa.

12
The Wave Nature of Light
  • What is the wavelength of yellow light with a
    frequency of 5.09 x 1014 s-1? (Note s-1,
    commonly referred to as Hertz (Hz) is defined as
    cycles or waves per second.)

13
The Wave Nature of Light
  • What is the frequency of violet light with a
    wavelength of 408 nm?

14
  • What is the wavelength of WONY?
  • What is the wavelength of cell phone radiation?
    Frequency 850 MHz
  • What is the wavelength of a microwave oven?
    Frequency 2.45 GHz

15
The Photoelectric Effect
Light can cause ejection of e- from a metal
surface.
An anode () attracts e- Current is measured
16
The Photoelectric Effect
  • Einstein proposed that light
  • is quantized.
  • behaves like a stream of massless particles.
  • G. N. Lewis later named them photons.
  • Imagine photons (balls) hitting e- embedded in
    glue.
  • If the E of the ball
  • is low, it cant eject an e-.
  • exceeds the strength of the glue, an e- is
    released

Higher intensity more photons (balls). If E gt
threshold, more balls eject more e-.
17
Quantization of Energy
Light acts as if it consists of particles called
PHOTONS, with discrete energy.
  • Energy of radiation is proportional to frequency

E h ?
h Plancks constant 6.6262 x 10-34 Js
18
E h ?
Relationships
19
Short wavelength light has
  1. High frequency and low energy
  2. High frequency and high energy
  3. Low frequency and low energy
  4. Low frequency and high energy

20
  • Rank the following in order of increasing photon
    energy
  •  
  • microwaves
  • radiowaves
  • X-rays
  • blue light
  • red light
  • UV light
  • IR light

21
Energy of Radiation
  • What is the frequency of UV light with a
    wavelength of 230 nm?
  • What is the energy of 1 photon of UV light with
    wavelength 230 nm?

22
What is the energy of a photon of 525 nm light?
  1. 3.79 x 10-19 J
  2. 4.83 x 10-22 J
  3. 3.67 x 1020 J
  4. 8.43 x 1023 J

23
Radio Wave Energy
  • What is the energy of a photon corresponding to
    radio waves of frequency 1.255 x 10 6 s-1?

24
  • What is the energy of a mole of 230 nm photons?
  • Can this light break C-C bonds with an energy of
    346 kJ/mol?

25
  • Does 1200 nm light have enough energy to break
    C-C bonds?

26
Where does light come from?
  • Excited solids emit a continuous spectrum of
    light
  • Excited gas-phase atoms emit only specific
    wavelengths of light (lines)

27
Light emitted by solids
28
Light emitted by hydrogen gas
29
The Bohr Model of Hydrogen Atom
  • Light absorbed or emitted is from electrons
    moving between energy levels
  • Only certain energies are observed
  • Therefore, only certain energy levels exist
  • This is the Quanitization of energy levels

30
Emission spectra of gaseous atoms
  • Excited atoms emit light of only certain
    wavelengths
  • The wavelengths of emitted light depend on the
    element.

31
Line spectra of atoms
32
Energy Adsorption/Emission
33
  • For H, the energy levels correspond to

Constant 2.18 x 10-18 J
Energy level diagram
34
Each line corresponds to a transition
  • Example n3 ? n 2

35
Explanation of line spectra
Balmer series
36
Bohr Model of the Hydrogen Atom
  • Heated solid objects emit continuous spectra.
  • Excited atomic gases emit line spectra.
  • Each element has a unique pattern.

37
Bohr Model of the Hydrogen Atom
  • Bohr (1913). The hydrogen e-

Niels Bohr
  • Orbits the nucleus.
  • Different orbits are possible with different
    quantized E values

Rydberg constant 2.179 x 10-18 J
If the e- has n 1 (lowest, most negative E),
the atom is in its ground state. If ionized (e-
removed), n ? (E 0).
38
Bohr Model of the Hydrogen Atom
absorption ?E gt 0, n ?
emission ?E lt 0, n ?
Bohrs model exactly predicts the H-atom spectrum.
39
Bohr Model of the Hydrogen Atom
Example Calculate the energy and wavelength (in
nm) for an H-atom n 4 ? n 2 transition.
40
Bohr Model of the Hydrogen Atom
Calculate E and wavelength (nm) for an H-atom n
4 ? n 2 transition.
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