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chemistry
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5.3
Physics and the Quantum Mechanical
Model
Neon advertising signs are
formed from glass tubes bent in
various shapes. An electric
current passing through the gas
in each glass tube makes the
gas glow with its own
characteristic color. You will
learn why each gas glows with a
specific color of light.
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5.3
Physics and the Quantum
Mechanical Model
>
Light
Light
How are the wavelength and frequency
of light related?
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5.3
Physics and the Quantum
Mechanical Model
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Light
• The amplitude of a wave is the wave’s height
from zero to the crest.
• The wavelength, represented by  (the Greek
letter lambda), is the distance between the
crests.
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Physics and the Quantum
Mechanical Model
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Light
• The frequency, represented by  (the Greek
letter nu), is the number of wave cycles to
pass a given point per unit of time.
• The SI unit of cycles per second is called a
hertz (Hz).
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5.3
Physics and the Quantum
Mechanical Model
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Light
The wavelength and frequency of light
are inversely proportional to each other.
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5.3
Physics and the Quantum
Mechanical Model
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Atomic Spectra
Atomic Spectra
What causes atomic emission spectra?
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5.3
Physics and the Quantum
Mechanical Model
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Atomic Spectra
When atoms absorb energy, electrons
move into higher energy levels. These
electrons then lose energy by emitting
light when they return to lower energy
levels.
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Mechanical Model
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Atomic Spectra
The frequencies of light emitted by an
element separate into discrete lines to give
the atomic emission spectrum of the
element.
Mercury
Nitrogen
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Physics and the Quantum
Mechanical Model
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An Explanation of Atomic Spectra
The light emitted by an electron moving
from a higher to a lower energy level has
a frequency directly proportional to the
energy change of the electron.
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Physics and the Quantum
Mechanical Model
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Quantum Mechanics
Quantum Mechanics
How does quantum mechanics differ
from classical mechanics?
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5.3
Physics and the Quantum
Mechanical Model
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Quantum Mechanics
In 1905, Albert Einstein successfully explained
experimental data by proposing that light could
be described as quanta of energy.
• The quanta behave as if they were particles.
• Light quanta are called photons.
In 1924, De Broglie developed an equation that
predicts that all moving objects have wavelike
behavior.
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5.3
Physics and the Quantum
Mechanical Model
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Quantum Mechanics
Today, the wavelike properties of beams of
electrons are useful in magnifying objects. The
electrons in an electron microscope have much
smaller wavelengths than visible light. This
allows a much clearer enlarged image of a very
small object, such as this mite.
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5.3
Physics and the Quantum
Mechanical Model
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Quantum Mechanics
Classical mechanics adequately
describes the motions of bodies much
larger than atoms, while quantum
mechanics describes the motions of
subatomic particles and atoms as waves.
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Physics and the Quantum
Mechanical Model
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Quantum Mechanics
The Heisenberg uncertainty principle states
that it is impossible to know exactly both the
velocity and the position of a particle at the same
time.
• This limitation is critical in dealing with small
particles such as electrons.
• This limitation does not matter for ordinarysized object such as cars or airplanes.
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5.3
Physics and the Quantum
Mechanical Model
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Quantum Mechanics
The Heisenberg Uncertainty Principle
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