Outline Chapter 8 The Atom

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Outline Chapter 8 The Atom
8-1. Photoelectric Effect 8-2. Photons 8-3.
What Is Light? 8-4. X-rays 8-5. De Broglie
Waves 8-6. Waves of What? 8-7. Uncertainty
Principle 8-8. Atomic Spectra
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8-2. Photons
Max Planck (1858-1947)
Max Planck in 1900 stated that the light emitted
by a hot object (black body radiation) is given
off in discrete units or quanta. The higher the
frequency of the light,the greater the energy per
quantum.
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8-2. Photons
The system shown here detects people with fevers
on the basis of their infrared emissions, with
red indicating skin temperatures above normal.
In this way people with illnesses that may be
infectious can be easily identified in public
places.
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8-2. Photons
All the quanta associated with a particular
frequency of light have the same energy. The
equation is E hf where E energy, h
Planck's constant (6.63 x 10-34 J s), and f
frequency.
Electrons can have only certain discrete
energies, not energies in between.
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8-1. The Photoelectron Effect
The photoelectric effect is the emission of
electrons from a metal surface when light shines
on it. The discovery of the photoelectric effect
could not be explained by the electromagnetic
theory of light. Albert Einstein developed the
quantum theory of light in 1905.
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8-2. Photons
Albert Einstein (1879-1955)
Einstein expanded Planck's hypothesis by
proposing that light could travel through space
as quanta of energy called photons. Einstein's
equation for the photoelectric effect is hf KE
w. Although photons have no mass and travel
with the speed of light, they have most of the
other properties of particles. The higher the
frequency (or shorter the wavelength) the higher
the energy.
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8-3. What is light?
Light exhibits either wave characteristics or
particle (photon) characteristics, but never both
at the same time. The wave theory of light and
the quantum theory of light are both needed to
explain the nature of light and therefore
complement each other.
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8-4. X-rays
Wilhelm Roentgen accidentally discovered x-rays
in 1895. In 1912, Max von Laue showed that x-rays
are extremely high frequency em waves. X-rays are
produced by high energy electrons that are
stopped suddenly the electron KE is transformed
into photon energy.
Wilhelm Roentgen (1845-1923)
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8-5. De Broglie Waves
Louis de Broglie(1892-1987)
In 1924, the French physicist Louis de Broglie
proposed that moving objects behave like waves
these are called matter waves. The de Broglie
wavelength of a particle of mass m and speed v is
l h/mv.
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8-5. De Broglie Waves
An electron Microscope and a micrograph of
bacteriophage viruses approximately 1 µm across.
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8-6. Waves of What?
The quantity that varies in a matter wave is
called the wave function (y). The square of the
wave function (y2) is called the probability
density. For a given object, the greater the
probability density at a certain time and place,
the greater the likelihood of finding the object
there at that time. The de Broglie waves of a
moving object are in the form of a group, or
packet, of waves that travel with the same speed
as the object.
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8-7. The Uncertainty Principle
The uncertainty principle states that it is
impossible to know both the exact position and
momentum of a particle at the same time. The
discoverer of the uncertainty principle was
Werner Heisenberg. The position and motion of any
object at a given time can only be expressed as
probabilities.
Werner Heisenberg (1901-1976)
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8-8. Atomic Spectra
A spectroscope is an instrument that disperses
the light emitted by an excited gas into the
different frequencies the light contains.
refraction
Light with multiple wavelengths
Wavelengths separated
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8-8. Atomic Spectra
An emission spectrum consists of the various
frequencies of light given off by an excited
substance. Below is the part of the emission
spectra of sodium.
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Emission Line Spectra of Some Common Elements
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8-8. Atomic Spectra
An absorption spectrum consists of the various
frequencies absorbed by a substance when white
light is passed through it. The frequencies in
the spectrum of an element fall into sets called
spectral series. Seen here is the spectral series
of hydrogen.
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Outline Chapter 8 The Atom
8-9. The Bohr Model 8-10. Electron Waves and
Orbits 8-11. The Laser 8-12. Quantum Mechanics
8-13. Quantum Numbers 8-14. Exclusion Principle
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8-9. The Bohr Model
The Niels Bohr model of the atom, proposed in
1913, suggested that an electron in an atom
possesses a specific energy level that is
dependent on the orbit it is in. An electron in
the innermost orbit has the least energy. He
predicted that the distance from the proton to
the electron in a hydrogen atom was about 0.89Å.
Niels Bohr (1884-1962)
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8-9. The Bohr Model
Electron orbits are identified by a quantum
number n, and each orbit corresponds to a
specific energy level of the atom. An atom having
the lowest possible energy is in its ground
state an atom that has absorbed energy is in an
excited state.
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8-10. Electron Waves and Orbits
When an electron "jumps" from one orbit (energy
level) to another, the difference in energy
between the two orbits is hf, where h is Plancks
constant and f is the frequency of the emitted or
absorbed light.
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Origin of Absorption Spectra
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8-10. Electron Waves and Orbits
An electron can circle a nucleus only in orbits
that contain a whole number of de Broglie
Wavelengths. The quantum number n of an orbit is
the number of electron waves that fit into the
orbit.
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8-10. Electron Waves and Orbits
Electrons seemed to be locked into these wave
patterns around the nucleus.
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8-11. The Laser
The word laser comes fromlight amplification by
stimulated emission of radiation.
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8-11. The Laser
Excitation Methods include electrical charge,
light (below), and chemical reaction.
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8-11. The Laser
Lasers are used in light shows.and eye surgery.
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8-11. The Laser
Holograms are made from laser light without using
an image forming device. The image formed
becomes 3D.
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8-11. The Laser
Holograms are made from laser light without using
an image forming device. The image formed
becomes 3D. Meet Mika..(Artoolkit)
http//www.youtube.com/watch?v7Ot4xFhvYNwfeature
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fvw
http//www.youtube.com/watch?voiqIPXnKkKofeature
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http//www.youtube.com/watch?vsPDUMRLcfdgfeature
related
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8-12. Quantum Mechanics
Erwin Schrödinger (1887-1961)
The theory of quantum mechanics was developed by
Erwin Schrödinger, Werner. According to quantum
mechanics, the position and momentum of a
particle cannot both be accurately known at the
same time. Only its most probable position or
momentum can be determined.
The most probable distance between the proton and
electron for a hydrogen atom turns out to be
about 0.89Å, the same as Niels Bohr.
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8-13. Quantum Numbers
1. The principal quantum number n governs the
electron's energy and average distance from the
nucleus. 2. The orbital quantum number l
determines the magnitude of an atomic electron's
angular momentum. 3. The magnetic quantum number
ml specifies the direction of an atomic
electron's angular momentum. 4. The spin magnetic
quantum number ms of an atomic electron has two
possible values, 1/2 or -1/2, depending on
whether the electron aligns itself along a
magnetic field (1/2) or opposite to the field
(-1/2).
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8-13. Quantum Numbers
principal quantum number n
1,2,3,.. orbital quantum number l
0,1,2,.n-1 magnetic quantum number m -l to l
for n2 -2,-1,0,1,2spin magnetic quantum
number ½ or ½ spin Its like your address. To
find where you are you need to know 4 things
state, city, street, house . To know where or
what state the electron is in you need to know
the four quantum numbers.
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Quantum s are like an Address.
What do you need to know to find out where you
live?
State
City
Street
House
Magnetic Quantum (ml)
Spin Quantum (ms)
Principle Quantum (n)
Angular Quantum (l)
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8-13. Quantum Numbers
3py
3d
2py
1s
3s
2s
2px
3px
3pz
2pz
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8-13. Quantum Numbers
The outside of the2s orbital can be seen below.
The 2p orbital is in the middle. A combination
of the 3 2p orbitals is shown in the movie on the
right.
Movie
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Scanning Tunneling Microscope
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Scanning Tunneling MicroscopeElectron Clouds
Image Movie
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8-14. The Exclusion Principle
The exclusion principle, first proposed by
Wolfgang Pauli in 1925, states that only one
electron in an atom can exist in a given quantum
state. Each atomic electron must have a different
set of quantum numbers n, l, ml, and ms.
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Fig. 8.37
Magnetic resonance imaging (MRI) is a method of
mapping tissue density based on proton spin that
shows the nature of soft tissue better than
x-rays.