#### Transcript Physics and the Quantum Mechanical Model

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5.3
Physics and the Quantum Mechanical
Model
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
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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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5.3
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
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Light
The wavelength and frequency of light are
inversely proportional to each other.
As wavelength (λ) increases, frequency decreases.
As wavelength (λ) decreases, frequency increases.
increases.
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5.3
Physics and the Quantum
Mechanical Model
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Light
The product of the frequency and wavelength
always equals a constant (c), the speed of light.
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5.3
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Light
According to the wave model, light consists of
electromagnetic waves.
visible light (ROY G BIV), ultraviolet waves, Xrays, and gamma rays. (add sketch slide 10)
• All electromagnetic waves travel in a vacuum
at a speed of 2.998  108 m/s.
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5.3
Physics and the Quantum
Mechanical Model
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Light
Sunlight consists of light with a continuous range
of wavelengths and frequencies.
• When sunlight passes through a prism, the
different frequencies separate into a
spectrum of colors.
• In the visible spectrum, red light has the
longest wavelength and the lowest frequency.
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5.3
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Light
The electromagnetic spectrum consists of radiation over
a broad band of wavelengths. P 139.
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Physics and the Quantum
Mechanical Model
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Light
Simulation 3
Explore the properties of electromagnetic
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SAMPLE PROBLEM 5.1
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SAMPLE PROBLEM 5.1
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SAMPLE PROBLEM 5.1
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SAMPLE PROBLEM 5.1
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Practice Problems for Sample Problem 5.1
Problem-Solving 5.15 Solve
Problem 15 with the help of an
interactive guided tutorial.
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5.3
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Mechanical Model
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Atomic Spectra
Atomic Spectra
What causes atomic emission spectra?
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Atomic Spectra
When atoms absorb energy, electrons
move into higher energy levels. These
electrons then lose energy by emitting
levels.
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Atomic Spectra
A prism separates light into the colors it contains.
When white light passes through a prism, it
produces a rainbow of colors.
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5.3
Physics and the Quantum
Mechanical Model
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Atomic Spectra
When light from a helium lamp passes through a
prism, discrete lines are produced.
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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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5.3
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An Explanation of Atomic Spectra
An Explanation of Atomic Spectra
How are the frequencies of light an atom
emits related to changes of electron
energies?
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An Explanation of Atomic Spectra
In the Bohr model, the lone electron in the hydrogen
atom can have only certain specific energies.
• When the electron has its lowest possible
energy, the atom is in its ground state.
• Excitation of the electron by absorbing energy
raises the atom from the ground state to an
excited state.
• A quantum of energy in the form of light is
emitted when the electron drops back to a lower
energy level. See p. 143, figure 5.14
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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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An Explanation of Atomic Spectra
The three groups of lines in the hydrogen
spectrum correspond to the transition of
electrons from higher energy levels to lower
energy levels. See p. 143.
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Physics and the Quantum
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An Explanation of Atomic Spectra
Animation 6
Learn about atomic emission spectra and how
neon lights work.
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5.3
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Quantum Mechanics
Quantum Mechanics
How does quantum mechanics differ
from classical mechanics?
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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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Physics and the Quantum
Mechanical Model
What is light?
>
Light is a particle - it comes in chunks.
Light is a wave - we can measure its
wavelength and it behaves as a wave
If we combine E=mc2 , c=f, E = 1/2 mv2 and E
= hf, then we can get:
 = h/mv
(from Louis de Broglie)
called de Broglie’s equation
Calculates the wavelength of a particle.
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Physics and the Quantum
Wave-Particle
Duality Model
Mechanical
>
J.J. Thomson won the Nobel prize for describing the
electron as a particle.
His son, George Thomson won the Nobel prize for
describing the wave-like nature of the electron.
The
electron is
a particle!
The electron
is an energy
wave!
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Physics and the Quantum
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Confused? You’ve Got Company!
“No familiar conceptions can be
woven around the electron;
something unknown is doing we
don’t know what.”
Physicist Sir Arthur Eddington
The Nature of the Physical World
1934
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Physics and the Quantum
Mechanical Model
The physics of the very small
>
Quantum mechanics explains how very
small particles behave
• Quantum mechanics is an explanation
for subatomic particles and atoms as
waves
Classical mechanics describes the
motions of bodies much larger than
atoms
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5.3
Physics and the Quantum
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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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Physics and the Quantum
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Quantum Mechanics
Simulation 4
Simulate the photoelectric effect. Observe the
results as a function of radiation frequency
and intensity.
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5.3
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Quantum Mechanics
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
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Heisenberg Uncertainty
Principle
“One cannot simultaneously
determine both the position
and momentum of an
electron.”
Werner Heisenberg
You can find out where the
electron is, but not where it is
going.
OR…
You can find out where the
electron is going, but not where
it is!
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5.3
Physics and the Quantum
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Quantum Mechanics
The Heisenberg Uncertainty Principle
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5.3
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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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Physics and the Quantum
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Physics and the Quantum >
Mechanical
It is more obvious
withModel
the very small objects
To measure where a electron is, we use
light.
But the light energy moves the electron
And hitting the electron changes the
frequency of the light.
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5.3 Section Quiz.
Assess students’ understanding
of the concepts in Section 5.3.
Continue to:
-or-
Launch:
Section Quiz
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5.3 Section Quiz.
1. Calculate the frequency of a radar wave with
a wavelength of 125 mm.
a. 2.40 109 Hz
b. 2.40 1024 Hz
c. 2.40 106 Hz
d. 2.40 102 Hz
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5.3 Section Quiz.
2. The lines in the emission spectrum for an
element are caused by
a. the movement of electrons from lower to
higher energy levels.
b. the movement of electrons from higher to
lower energy levels.
c. the electron configuration in the ground
state.
d. the electron configuration of an atom.
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5.3 Section Quiz.
3. Spectral lines in a series become closer
together as n increases because the
a. energy levels have similar values.
b. energy levels become farther apart.
c. atom is approaching ground state.
d. electrons are being emitted at a slower
rate.
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www.chembored.com
Chem 12
Quantum mechanics: the sequel
Overlapping shells slide: slide 9 (this is the 2nd
day of the quantum mechanics lesson).
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