Download Chapter 9 The Atom - Bakersfield College

Outline Chapter 9 The Atom
9-1. Photoelectric Effect
9-2. Photons
9-3. What Is Light?
9-4. X-rays
9-5. De Broglie Waves
9-6. Waves of What?
9-7. Uncertainty Principle
9-8. Atomic Spectra
9-9. The Bohr Model
9-10. Electron Waves/Orbits
9-11. The Laser
9-12. Quantum Mechanics
9-13. Quantum Numbers
9-14. Exclusion Principle
9-2. 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.
9-2. 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.
9-2. 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.
9-1. 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.
9-2. 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.
9-3. 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.
9-4. 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)
9-5. De Broglie Waves
1924 – Nobel Prize in 1929
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.
• An 18-wheeler moving down Hwy 99 at 60mph has a
wavelength smaller than an atom.
• However, an electron (very light) moves much faster and
its wavelength is much larger than its size.
9-5. De Broglie Waves
An electron Microscope and a micrograph of
bacteriophage viruses approximately 1 μm across.
9-6. 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.
9-7. 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)
9-8. Atomic Spectra
A spectroscope is an instrument that disperses the
light emitted by an excited gas into the different
frequencies the light contains.
refraction
Wavelengths
separated
9-8. 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.
Emission Line Spectra of Some Common
Elements
9-8. 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.
9-9. 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)
9-9. 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.
9-10. 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
Planck’s constant
and f is the
frequency of the
emitted or
absorbed light.
Origin of Absorption Spectra
9-10. 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.
9-10. Electron Waves and Orbits
Electrons seemed
to be locked into
these wave patterns
around the nucleus.
9-11. The Laser
The word laser
comes from
light
amplification by
stimulated
emission of
radiation.
9-11. The Laser
Excitation Methods include electrical charge, light
(below), and chemical reaction.
9-11. The Laser
Lasers are used in
light shows and eye
surgery.
9-11. The Laser
Holograms are made from laser light without
using an image forming device. The image
formed becomes 3D.
Holograms
3D pictures made by Lasers using the interference pattern
between reflected laser light from the surface of an object and
the undisturbed laser light reflected from a mirror. The
Interference pattern is recorded on film. The developed film can
then be used by a laser to recreate the image in 3D.
http://www.youtube.com/watch?v=3d7sQfIBAwk
http://www.youtube.com/watch?v=E4A_u67EKnU&feature=fvw
http://www.youtube.com/watch?v=cAX8uSc8Fnk&NR=1
http://www.youtube.com/watch?v=jIcsYBZSQ48
Holograms
Holograms are made from laser light without
using an image forming device. Tupac
holographic concert and a holographic
fashion display.
http://www.youtube.com/watch?v=mcSYpZchFpI
http://www.youtube.com/watch?v=Zf_eXDPElh0
30
9-11. 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?v=7Ot4xFhvYNw&feature=related
http://www.youtube.com/watch?v=JvufPRbQsXA&feature=fvw
http://www.youtube.com/watch?v=oiqIPXnKkKo&feature=related
http://www.youtube.com/watch?v=sPDUMRLcfdg&feature=related
9-12. 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.
9-13. 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).
9-13. 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 n=2 -2,-1,0,1,2
spin 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.
Quantum #’s are like an
Address.
What do you need to know to find out where you live?
State
Principle
Quantum # (n)
City
Angular
Quantum # (l)
Street
Magnetic
Quantum # (ml)
House
Spin Quantum #
(ms)
9-13. Quantum Numbers
3py
3d
2py
1s 2s
2px
2pz3pz
3s
3px
9-13. 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
Scanning Tunneling Microscope
Scanning Tunneling Microscope
Electron Clouds
Image Movie
9-14. 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.
Fig. 9.37
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.