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Electromagnetic Radiation and Light

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Title: Quantum Theory of the Atom Author: whs Last modified by: Ponce, Keri Created Date: 10/16/2008 4:33:45 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Electromagnetic Radiation and Light


1
Electromagnetic Radiationand Light
2
I. Models of the Atom
  • Many different models
  • Dalton-billiard ball model (1803)
  • Thompson plum-pudding model (1897)
  • Rutherford Nuclear model of the atom (1911)
  • Bohr uses quantized energy of the atom (1913)
  • Quantum Mechanical Model of the Atom (1926)

3
  • Each new model contributed to the model we use
    today.
  • Even our current model, does not give us an exact
    model of how electrons behave.

4
A. The Bohr Model
  • Bohr used the simplest element, hydrogen, for his
    model
  • Proposed electron is found in specific circular
    paths, or orbits around the nucleus
  • Each electron orbit was
  • thought to have a fixed
  • energy level.
  • Lowest level-ground state
  • Any Higher Level-
  • excited state

5
The Bohr Model cont.
  • One electron is capable of many different excited
    states (e- jumping to higher level)
  • Quantum specific amount of energy an e- can gain
    or lose when moving energy levels
  • You can excite an e- with energy like
    electricity, the sun, or magnets

Electron dropping from higher level to
lower-releases energy
energy
6
B. Problems with the Bohr Model
  • OOPS!- Model only works with hydrogen
  • Did not account for the chemical behavior of
    atoms
  • WRONG Electrons do not move around the nucleus
    in circular orbits
  • Still very helpful!!

7
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8
II. How do Neon Signs work?
  • They have excited gases in them.

9
Explanation
Step 2
  • Step 1 an electron absorbs energy and moves to a
    higher energy level
  • Step 2 e- drops back down to a lower energy
    level
  • During drop it gives off energy called a photon
  • Sometimes this energy is visible light (ROYGBIV)

Step 1
  • When a photon is emitted, energy is released. We
    can calculate the energy released using the
    equation E h ? ?

10
Application Atomic Emission Spectrum
  • Used to determine which elements are present in a
    sample
  • Used to determine which elements are present in a
    star (because stars are gases)
  • Each element has a unique spectrum
  • Only certain colors are emitted because the
    energy released relates to specific frequency

11
Spectroscope
  • A spectroscope is needed to see the atomic
    emission spectra, which acts similar to a prism,
    separating different frequencies of light

12
Electromagnetic Spectrum
  • Electromagnetic spectrum is the range of all
    energies emitted from photons acting like waves.

13
Electromagnetic Spectrum with Visible Light
Spectrum
14
Lab Atomic Emission Spectra of Several Gases
15
Light
  • Behaves like a particle
  • Behaves like a wave

16
Characteristics of a Wave
  • Wavelength ? (lambda) shortest distance between
    equivalent points on a continuous wave Unit
    meters
  • Frequency ? (nu) the number of waves that pass
    a given point per second Unit 1/second s-1
    Hertz (Hz)
  • Crest Highest point of a wave
  • Trough Lowest point of a wave
  • Amplitude (a) height from its origin to its
    crest (highest point) or trough (lowest point)
    Unit meters

17
Wavelength and Frequency
  • Wavelength (?) and frequency (?) are related
  • As wavelength goes up, frequency goes down
  • As wavelength goes down, frequency goes up
  • This relationship is inversely proportional

18
Wavelength and Frequency cont.
c
  • c ??
  • Speed of light (c) 3 x 108 m/s

Speed of light
  • c ??
  • c / ?
  • ? c / ?

?
?
wavelength
frequency
19
Question Time
  • Calculate the wavelength (?) of yellow light if
    its frequency (?) is 5.10 x 1014 Hz.

c
20
Question Time
  • What is the frequency (?) of radiation with a
    wavelength (?) of 5.00 x 10-8 m? What region of
    the electromagnetic spectrum is this radiation?

c
21
How Much Energy Does a Wave Have?
  • Energy of a wave can be calculated
  • Use the formula E h??
  • E Energy
  • ? frequency
  • h Plancks constant 6.626 x 10-34 Joule .
    Sec
  • Joule is a unit for energy (J)
  • Energy and frequency are directly proportional,
    as frequency increases, energy increases

22
Question Time
  • Remember that energy of a photon given off by an
    electron is E h?
  • How much energy does a wave have with a frequency
    of 2.0 x 108 Hz? ( h 6.626 x 10-34 J.s)

E 1.3 x 10-34 Joule
23
Visible Light, Frequency, and Energy
  • Red longest wavelength (?),
  • smallest frequency (?)
  • Red frequency smallest (?),
  • least amount of energy (E)
  • Violet smallest wavelength (?),
  • largest frequency (?)
  • Violet frequency largest (?),
  • greatest amount of energy (E)

24
Flame Test
  • The flame test is a way to determine the element
    present in a sample
  • When placed in a flame, each element gives off a
    different color
  • Operates same as neon signs electrons excited by
    heat and fall back down and give off different
    colors.
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