Transcript Chapter 5 PPT

Light
Light Is a Wave
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Amplitude is the height of the wave from
zero to the crest or from zero to the trough
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Wavelength is the length between waves
(how’s that for a definition)
Measure crest to crest or trough to trough
Symbolized with the Greek letter lambda
(λ)
Greek Lamb
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Frequency is the number of waves that
pass a given point over a period of time
Commonly measured in the unit Hertz (Hz)
or sometimes in s-1
Symbolized with the letter f
The speed of light is 3 x 108 m/s
 Symbolized with the letter “c” (latin celeritas =
swift)
 We can draw a relationship between wavelength
and frequency with the following equation:
c = λf
Q: What type of relationship does this represent?
A: Inverse
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Try this one!
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X-rays emitted by Cu have a wavelength of
1.54 x 10-8cm. What is the frequency of this
radiation?
DO
WORK!
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Answer…
1.95 x 1018 sec–1 (Hz)
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Calculate the wavelength of yellow light
emitted by a sodium lamp. The frequency is
5.0 x 1014 Hz.
Answer…
6.0 x 10-7m
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What is the wavelength of radiation with a
frequency of 1.50 x 1013 Hz?
Answer…
2.00 x 10-5m
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What frequency is radiation with a
wavelength of 5.00 x 10-8m?
Answer…
6.00x1015 Hz
The Electromagnetic Spectrum
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See Page 139 in your book!
Made up of radio, micro, infrared, visible
light, ultraviolet, X-rays, and gamma rays
Visible light makes up only a small portion
Can be separated into its constituent colors
by using a prism.
Atomic Spectra
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Emission Spectra (also
referred to as bright line
spectra) are the frequencies
of light emitted by an element
separated into discrete lines
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Continuous Spectrum is all
wavelengths within a given range
(usually applied to ROYGBIV)
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Absorption Spectra are
discreet energies absorbed
from the continuous spectrum
by electrons of a specific
element
Recap…
When atoms absorb energy, electrons move into
higher energy levels
Atoms emit energy when they return to lower
energy levels, sometimes in the form of light
Atomic emission spectrum – the frequencies of light
emitted by an element separated into discrete
lines
Emission spectrums are the “fingerprint” of an atom
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Louis de Brolglie predicted that light can
behave as a wave as well as a particle.
Known as the Wave-Particle Duality Theory
The Photoelectric Effect occurs when
electrons are released from a metal when
light is shone on it.
This only occurs with certain frequencies of
light.
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Max Planck and Albert Einstein (19001905) demonstrated that light behaves as
if it were composed of tiny “packets” of
energy called QUANTA or PHOTONS
Energy of a photon (absorbed or emitted)
is proportional to the frequency of light
We can represent this relationship with an
equation!
 E = hf
 h is known as Planck’s constant.
 h = 6.63x10-34J s
Q: What type of relationship exists between
energy and frequency?
A: Direct
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Try these…
Calculate the frequency of a photon with energy
4.55x10-23 J.
E = hf
f = E/h
f = 4.55x10-23 J
6.63x10-34 J s
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f = 6.86x1010 Hz
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Calculate the energy of a photon whose
frequency is 3.20x1011s-1
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Answer…
2.12x10-22J
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Inadequacies of Bohr’s Model
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Much like the other models of the atom
Bohr’s model had many weaknesses
Could only explain the spectra of single
atoms with one electron
Could not explain why some emission lines
are brighter than others
As we mentioned before…
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The quantum mechanical model
Electron clouds house electrons 90% of the
time
Based on Schrödinger's equations
Werner Heisenberg also contributed to the
Quantum mechanical model
Heisenberg was the head of the German
Nuclear Energy Project under the Nazi
regime.
 Heisenberg Uncertainty Principle states
that its impossible determine velocity and
position of an electron.
 Epitaph reads,
“He lies somewhere here”
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