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Title: Know:


1
  • Know
  • Definitions of photon and Plancks Constant.
  • Energy/mass relationship equation.
  • Only certain energy levels are permitted in
    atoms.
  • Definitions of hadron baryon meson lepton
    and quark.
  • Understand
  • The manner in which the Photoelectric Effect
    demonstrates the particle nature of light.
  • The connection between energy and mass and the
    fact that energy and mass can be converted into
    one another.
  • An atom may be ionized (lose an electron) if it
    absorbs a photon with great enough energy.
  • An electron may jump to a higher energy level if
    it is hit with a photon with the correct energy
    to make the transition this causes atoms to
    ABSORB photons with very specific energies.
  • An electron in an excited state will naturally
    decay to a lower energy state, releasing a photon
    with energy equal to the difference in energy
  • between the levels this causes atoms to EMIT
    photons with very specific energies.
  • All particles have corresponding anti-particles
    with equal mass and opposite charge.
  • A baryon is a collection of three quarks.
  • A meson is a pairing of a quark and an
    anti-quark.
  • Leptons are indivisible and have a charge of -1
    or 0.
  • Strong nuclear force holds the nuclei of atoms
    together and is carried by gluons.
  • Weak nuclear force is involved in beta decay and
    is carried by bosons.
  • Electromagnetic force governs interactions
    between atoms forms molecules gives matter its
    shape and is carried by photons.

2
Light as a wave
  • Light is an electromagnetic wave produced by an
    oscillating _______________________. The
    vibrating charges produce alternating
    _________________________________which are
    perpendicular to the direction of the waves
    motion. This waves can travel through vacuum in
    vast space.
  • Light is a wave because
  • Light have wave characteristics such as
    _________________________________________________
  • Light exhibit wave behavior such as
    _________________________________________________
  • However, the wave model of light can not explain
    interactions of light with matter

electric charges
electric and magnetic fields
amplitude, wavelength, frequency, and velocity.
diffraction, interference, and the Doppler effect.
3
An unusual phenomenon was discovered in the early
1900's. If a beam of light is pointed at the
negative end of a pair of charged plates, a
current flow is measured. A current is simply a
flow of electrons in a metal, such as a wire.
Thus, the beam of light must be liberating
electrons from one metal plate, which are
attracted to the other plate by electrostatic
forces. This results in a current flow.
Waves have a particle nature
An unusual phenomenon was discovered in the early
1900's. Photoelectric_Effect If a beam of light
is pointed at the negative end of a pair of
charged plates, a current flow is measured which
means the beam of light must be liberating
electrons from one metal plate, which are
attracted to the other plate by electrostatic
forces. However, the observed phenomenon was
that the current flow varied strongly with the
frequency of light such that there was a sharp
cutoff and no current flow for smaller
frequencies. Only when the frequency is above a
certain point (threshold frequency), the current
flow increases with light strength.
Photoelectric Effect
4
example
Which graph best represents the relationship
between the intensity of light that falls on a
photo-emissive surface and the number of
photoelectrons that the surface emits? 
1 2 3 4
5
example
  • When the source of a dim orange light shines on a
    photosensitive metal, no photoelectrons are
    ejected from its surface.  What could be done to
    increase the likelihood of producing
    photoelectrons?
  • Replace the orange light source with a red light
    source.
  • Replace the orange light source with a higher
    frequency light source.
  • Increase the brightness of the orange light
    source.
  • Increase the angle at which the photons of orange
    light strike the metal.

6
example
A beam of monochromatic light incident on a metal
surface causes the emission of photoelectrons. 
The length of time that the surface is
illuminated by this beam is varied, but the
intensity of the beam is kept constant.  Which
graph below best represents the relationship
between the total number of photoelectrons
emitted and the length of time of illumination?
1
3
2
4
7
Einstein explains photoelectric effect
  • ..\..\RealPlayer Downloads\Photoelectric Effect
    and Photoelectric Cell.flv
  • Einstein successful explained the photoelectric
    effect within the context of the new physics of
    the time, quantum physics developed by Max
    Planck.
  • Quantum theory assumes that electromagnetic
    energy is emitted from and absorbed by matter in
    discrete amounts of packets. Each packet carries
    a quantum of energy.
  • The quantum, or basic unit, of electromagnetic
    energy is called a photon. A photon is a
    mass-less particle of light, it carries a quantum
    of energy.

Energy E hf
8
Energy E hf
  • since f c/? E hf hc/?
  • The amount of energy E of each photon is directly
    proportional to the frequency f of the
    electromagnetic radiation, and inversely
    proportional to the wavelength ?.
  • E is energy of a photon, in Joules, or eV,
  • 1 eV 1.60x10-19 J
  • h is Plancks constant, 6.63 x 10-34 Js
  • f is frequency of the photon, in hertz
  • c is the speed of light in vacuum, c 3.00x108
    m/s
  • ? is wavelength, in meters

9
example
  • Which characteristic of electromagnetic radiation
    is directly proportional to the energy of a
    photon?
  • wavelength
  • period
  • frequency
  • path

10
Example
  • The energy of a photon is 2.11 electronvolts
  • Determine the energy of the photon in Joules
  • Determine the frequency of the photon
  • Determine the color of light associated with the
    photon.

11
example
  • The slope of a graph of photon energy versus
    photon frequency represents
  • Plancks constant
  • the mass of a photon
  • the speed of light
  • the speed of light squared

12
The Compton effect photon-particle collision
  • In 1922 Arthur Compton was able to bounce an
    X-ray photon off an electron.  The result was an
    electron with more kinetic energy than it started
    with, and an X-ray with less energy than it
    started with.  A photon can actually interact
    with a particle!  A photon has momentum!!  -
    another proof that photon is a particle.
  • During the collision, both energy and momentum
    are conserved.

13
The momentum of a photon
  • A photon, although mass-less, it has momentum as
    well as energy. All photons travel at the speed
    of light, c. The momentum of photon is
  • p h/? hf/c
  • Where p is momentum,
  • h is planks constant,
  • ? is the wavelength
  • Momentum p is directly proportional to the
    frequency light, and inversely proportional to
    the wavelength.

p h/? hf/c
E hc/? hf
14
example
  • A photon of light carries
  • energy, but not momentum
  • momentum, but not energy
  • both energy and momentum
  • neither energy nor momentum

15
example
  • All photons in a vacuum have the same
  • speed
  • wavelength
  • energy
  • frequency

16
example
  • The threshold frequency of a photo emissive
    surface is 7.1 x 1014 hertz.  Which
    electromagnetic radiation, incident upon the
    surface, will produce the greatest amount of
    current?
  • low-intensity infrared radiation
  • high-intensity infrared radiation
  • low-intensity ultraviolet radiation
  • high-intensity ultraviolet radiation

17
  • In conclusion, light has both wave and particle
    nature.
  • Wave nature
  • Exhibit wave characteristics
  • __________________________________________________
    _____
  • Exhibit wave behavior
  • _______________________________________________
  • Particle nature
  • ________________________________________
  • _________________________________
  • _________________________________

18
Particles have wave nature
  • Just as radiation has both wave and particle
    characteristics, matter in motion has wave as
    well as particle characteristics.
  • The wavelengths of the waves associated with the
    motion of ordinary object is too small to be
    detected.
  • The waves associated with the motion of particles
    of atomic or subatomic size, such as electrons,
    can produce diffraction and interference patterns
    that can be observed.

19
All Matters have wave nature
  • All matters have wave nature.
  • Louis de Broglie (French physicist and a Nobel
    laureate) assumed that any particle--an electron,
    an atom, a bowling ball, whatever--had a
    "wavelength" that was equal to Planck's constant
    divided by its momentum...

? h / p
20
In summary
  • Waves has particle nature, it has momentum just
    like a particle
  • Particle has wave nature, it has a wavelength
    just like a wave

p h / ?
? h / p
21
models of an atom
  1. Describe Thompsons model
  2. Explain the strengths and weaknesses of
    Rutherfords model of the atom
  3. Describe Bohr model of an atom
  4. Describe cloud model

22
  • About 440BC, a Greek scientist named Democritus
    came up with the idea that eventually, all
    objects could be reduces to a single particle
    that could not be reduced any further.He called
    this particle an atom, from the Greek word atomos
    which meant not able to be divided.From this,
    the idea of the atom the basic building block
    of all matter was born.
  • Around 1700, scientists understanding of
    molecular composition of matter had grown
    considerably. They had figured out that elements
    combine together in specific ratios to form
    compounds. In 1803, British chemist John Dalton
    came up with a theory about atoms
  • All substances are made of small particles that
    cant be created, divided, or destroyed called
    atoms.
  • Atoms of the same element are exactly alike, and
    atoms of different elements are different from
    each other. (So, atoms of gold are exactly like
    gold atoms, but different than aluminum atoms).
  • Atoms join with other atoms to make new
    substances.

23
  • In 1897, a British scientist named JJ Thomson
    discovered that electrons are relatively
    low-mass, negatively charged particles present in
    atoms.
  • Because atoms are neutral, he proposed a model -
    the "atom" was made of negatively-charged
    particles (electrons) dispersed among
    positively-charged particles (protons) like
    raisins in "plums in a pudding".
  • In 1909, British scientist Ernest Rutherford
    decided to test the Thomson theory, and designed
    an experiment to examine the parts of an atom.

24
Rutherfords model
  • In his experiment, He fired alpha particles (2
    positive charges) beam at extremely thin gold
    foil.
  • He expected alpha particles travel in straight
    line unaffected because the net electric force on
    the alpha particle would be relatively small.
  • However, he found a small number of particles
    were scattered at large angles.
  • Rutherford explained this phenomenon by assuming
    the following
  • Most particles were not affected due to the vast
    empty space inside the atom
  • Only a few particles were scattered due to the
    repulsive force between the concentrated positive
    charge inside the atom and the particle.
  • Rutherfords model of the atom
  • most of the mass was concentrated into a compact
    nucleus (holding all of the positive charge),
    with electrons occupying the bulk of the atom's
    space and orbiting the nucleus at a distance.

25
  • In Rutherfords model of the atom, electrons
    orbit the nucleus in a manner similar to planets
    orbiting the sun.

26
example
  • The diagram represents alpha particle A
    approaching a gold nucleus.  D is the distance
    between the path of the alpha particle and the
    path for a head-on collision. If D is decreased,
    the angle of deflection ? of the alpha particle
    would
  • decrease
  • increase
  • remain the same

27
example
  • Which diagram shows a possible path of an alpha
    particle as it passes very near the nucleus of a
    gold atom?
  • 1
  • 2
  • 3
  • 4

28
example
  • In Rutherford's model of the atom, the positive
    charge
  • is distributed throughout the atom's volume
  • revolves about the nucleus in specific orbits
  • is concentrated at the center of the atom
  • occupies most of the space of the atom

29
Limitation of Rutherford model
  • According to Rutherford, electrons accelerate due
    to centripetal force, and the accelerating
    charges radiate electromagnetic waves, losing
    energy. So the radius of electrons orbit would
    steadily decrease.
  • This model would lead a rapid collapse of the
    atom as the electron plunged into the nucleus.

30
The Bohr Model of the hydrogen atom
  • Danish physicist Niels Bohr attempted to explain
    the problems in Rutherfords model. He proposed
    in 1913 that electrons move around the nucleus of
    an atom in specific paths, on different levels of
    energy.
  1. All forms of energy are quantized.
  2. The electron in an atom can occupy only certain
    specific orbits and no other.
  3. Electrons can jump from one orbit to another by
    emitting or absorbing a quantum of energy in the
    form of photon.
  4. Each allowed orbit in the atom corresponds to a
    specific energy level. The orbit nearest the
    nucleus represents the smallest amount of energy
    that the electron can have. The electron can
    remain in this orbit with out losing energy even
    though it is being accelerated.

31
  • When electron is in any particular orbit, it is
    said to be in a stationary state. Each stationary
    state represents an energy level. The successive
    energy levels of an atom are assigned integral
    numbers, denoted by n1, 2, 3
  • When the electron is in the lowest level (n1),
    it is said to be in the ground state.
  • For a hydrogen atom, an electron in any level
    above the ground state is said to be in an
    excited state.

32
  • When electron goes up from lower to higher level,
    the atom absorbs a quantum of energy in the form
    of a photon.
  • When electron goes down from higher to lower
    level, the atom emits a quantum of energy in the
    form of a photon.

33
  • If the energy of the photon of light is just
    right, it will cause the electron to jump to a
    higher level. 
  • When the electron jumps back down, a photon is
    emitted for each jump down. 
  • A photon without the right amount of energy (the
    pink one) passes through the atom with no effect.
  • Photons with too much energy will cause the
    electron to be ejected which ionizes the atom

34
  • Energy levels
  • excitation any process that raises the energy
    level of electrons in an atom.
  • Excitation can be the result of absorbing the
    energy of colliding particles of matter, such as
    electrons, or of photons of electromagnetic
    radiation.
  • A photons energy is absorbed by an electron in
    an atom only if the photons energy corresponds
    exactly to an energy-level difference possible
    for the electron.
  • Excitation energies are different for different
    atoms.

35
  • Atoms rapidly lose the energy of their various
    excited states as their electrons return to the
    ground state. This lost energy is in the form of
    photons of specific frequencies, which appear as
    the spectrum lines in the characteristic spectrum
    of each element.
  • A spectrum line is a particular frequency of
    absorbed or emitted energy characteristic of an
    atom.

Absorption Spectrum
Emission Spectrum
36
example
  • White light is passed through a cloud of cool
    hydrogen gas and then examined with a
    spectroscope. What is the cause of dark lines
    observed on a bright background?

37
  • Ionization potential
  • An atom can absorb sufficient energy to raise an
    electron to an energy level such that the
    electron is removed from the atoms bound and an
    ion is formed.
  • The energy required to remove an electron from an
    atom to form an ion is called the atoms
    ionization potential.
  • An atom in an excited state requires a smaller
    amount of energy to become an ion than does an
    atom in the ground state.

38
Energy level diagram
  • The energy level of an electron that has been
    completely removed from the atom is defined to be
    0.00 eV. All other energy levels have negative
    values.
  • The electron in the ground state has the lowest
    energy, with largest negative value.

ionization
Ground state
39
Ephoton Einitial - Efinal This formula can be used to determine the energy of the photon emitted () or absorbed(-).
Ephoton hf where h 6.63 x 10-34 Js This formula can be used to determine the energy of a photon if you know the frequency of it.  Planck's constant, h, can be used in terms of Joule(s) or eV(s). (note the Regents reference table only gives it in terms of  Js)
40
Energy level is explained by Louis de Broglies
particle-wave theory
  • According to de Broglie, particles have wave
    nature
  • ? h / p
  • If we begin to think of electrons as waves, we'll
    have to change our whole concept of what an
    "orbit" is. Instead of having a little particle
    whizzing around the nucleus in a circular path,
    we'd have a wave sort of strung out around the
    whole circle. Now, the only way such a wave could
    exist is if a whole number of its wavelengths fit
    exactly around the circle.
  • If the circumference is exactly as long as two
    wavelengths, say, or three or four or five,
    that's great, but two and a half won't cut it.


41
..\..\RealPlayer Downloads\Quantum Mechanics- The
Structure Of Atoms.flv
42
Limitations of Bohrs model
  • It can not predict or explain the electron orbits
    of elements having many electrons

43
The cloud model (Schrödinger model)
  • In this model, electrons are not confined to
    specific orbits, instead, they are spread out in
    space in a form called an electron cloud.
  • The electron cloud is densest in regions where
    the probability of finding the electron is
    highest.

The cloud model represents a sort of history of
where the electron has probably been and where it
is likely to be going. 
44
example
  • The term "electron cloud" refers to the
  • electron plasma surrounding a hot wire
  • cathode rays in a gas discharge tube
  • high-probability region for an electron in an
    atom
  • negatively charged cloud that can produce a
    lightning strike

45
Atomic spectra
  • Explain atomic spectra using Bohrs model of the
    atom.
  • Recognize that each element has a unique emission
    and absorption spectrum.

46
Atomic spectra
  • According to Bohrs model, electrons in atoms can
    be found in only certain discrete energy states.

47
Atomic spectra
  • When electrons jump from the lower to the higher
    number orbits, they absorb a particular amount of
    energy and we can observe the absorption
    spectrum.
  • When they fall back again they release the same
    amount of energy and we can observe the emission
    (bright-line) spectrum. The amount of energy
    absorbed or released in this way can be directly
    related to the wavelength at which we see the
    absorption and emission lines on the spectrum.

48
(No Transcript)
49
  • Each element has a characteristic spectrum that
    differs from that of every other element.
  • The emission spectrum can be used to identify the
    element, even when the element is mixed with
    other elements.

Hydrogen spectrum
Helium spectrum
50
Emission (bright-line, atomic) spectra
  • When an electron in an atom in an excited state
    falls to a lower energy level, the energy of the
    emitted photon is equal to the difference between
    the energies of the initial and final states.
  • Ephoton Ei Ef hf
  • Ei is the initial energy of the electron in its
    excited state and Ef is the final energy of the
    electron in the lower energy level.

51
  • Each energy difference between two energy levels
    corresponds to a photon having a specific
    frequency.
  • For example An electron in a hydrogen atom drops
    from the n 3 energy level to the n 2 energy
    level. The energy of the emitted photon is

52
A specific series of frequencies, characteristic
of the element, is produced when the electrons of
its atoms in excited states fall back to lower
states or to the ground state. When these
emitted frequencies appear as a series of bright
lines against a dark background, they are called
a bright-line spectrum or an emission spectrum.
53
example
  • An electron in a hydrogen atom drops from the n
    4 energy level to the n 2 energy level. The
    energy of the emitted photon is

54
example
  • Excited hydrogen atoms are all in the n 3
    state. How many different photon energies could
    possibly be emitted as these atoms return to the
    ground state?
  • 1
  • 2
  • 3
  • 4

55
example
  • What is the minimum amount of energy needed to
    ionize a mercury electron in the c energy level?

56
question
  • Which electron transition in the hydrogen atom
    results in the emission of a photon of greatest
    energy?
  •   n 2 to n 1
  •   n 3 to n 2
  •   n 4 to n 2
  •   n 5 to n 3

57
Absorption spectra
  • An atom can absorb only photons having energies
    equal to specific differences in its energy
    levels.
  • The frequencies and wavelengths of these absorbed
    photons are exactly the same as those of the
    photons emitted when electrons lose energy and
    fall between the same energy levels.

58
  • If the atoms of an element are subjected to white
    light, which consists of all the visible
    frequencies, the atoms will selectively absorb
    the same frequencies that they emit when excited.
    The absorbed frequencies appear as dark lines in
    the otherwise continuous white-light spectrum.
    The series of dark lines is called an absorption
    spectrum.

absorption Spectrum
59
example
A
The four-line Balmer series spectrum shown in the
diagram is emitted by a hydrogen gas sample in a
laboratory.  A star moving away from Earth also
emits a hydrogen spectrum.  Which spectrum might
be observed on Earth for this star?               
                                             
B
C
D
60
example
  • An electron in a mercury atom that is changing
    from the a to the g level absorbs a photon with
    an energy of
  • 12.86 eV
  • 10.38 eV
  • 7.90 eV
  • 2.48 eV

61
example
  • When an electron changes from a higher energy
    level to a lower energy level within an atom, a
    quantum of energy is
  • fission
  • fused
  • emitted
  • absorbed

62
nucleus
  1. Define nuclear force
  2. Describe universal mass unit
  3. Use mass-energy relationship in calculations

63
Nuclear force
  • ..\..\RealPlayer Downloads\Physical Science 7.4c
    - The Atomic Nucleus.flv
  • The nucleus is the core of an atom made up of one
    or more protons (except for one of the isotopes
    of hydrogen) and one or more neutron. The
    positively charged protons in any nucleus
    containing more than one proton are separated by
    a distance of 10-15 m.
  • In the nucleus, there are two major forces
  • A large repulsive electric (Coulomb) force
    between protons
  • A very strong attractive nuclear force to keep
    the protons together.
  • It is this nuclear force inside a nucleus that
    overcomes the repulsive electric force between
    protons and hold the nucleus together.

64
  • Nuclear force has rather unusual properties.
  • It is charge independent. This means that in all
    pairs neutron neutron, proton proton, and
    neutron proton, nuclear forces are the same.
  • at distances 10-13 cm, the nuclear force is
    attractive and very strong, 100 times stronger
    than the electromagnetic repulsion. Strongest
    forces known to exist, nuclear force is also
    called strong force.
  • the nuclear force very short range force. At
    distances greater than a few nucleon diameters,
    the nuclear attraction practically disappears. As
    the nucleus gets bigger, the attractive nuclear
    force between the nucleons gets smaller, the
    nucleus becomes very unstable and starts to break
    apart, causing radioactive decay.

65
example
  • Which type of force overcomes the repulsive
    electrostatic force between protons in the
    nucleus of an atom?
  • magnetic
  • nuclear
  • gravitational
  • centrifugal

66
example
  • The force that holds protons and neutrons
    together is known as the
  • gravitational force
  • strong force
  • magnetic force
  • electrostatic force

67
example
  • Compared to the gravitational force between two
    nucleons in an atom of helium, the nuclear force
    between the nucleons is
  • weaker and has a shorter range
  • weaker and has a longer range
  • stronger and has a shorter range
  • stronger and has a longer range

68
Universal mass unit
  • The universal mass unit, or atomic mass unit, is
    defined as 1/12 the mass of an atom of carbon-12,
    which is a carbon atom having 6 protons, 6
    neutrons, and 6 electrons.
  • In universal mass unit,
  • the mass of the proton is 1.0073 u,
  • the mass of the neutron is 1.0087 u,
  • the mass of an electron is 0.0005 u.
  • In SI units, a mass of one universal mass unit,
  • 1 u 1.66 x 10-27 kg.

69
example
  • An atomic mass unit is defined as 1/12 the mass
    of an atom of

70
Mass-energy relationship
  • Einstein showed that mass and energy are
    different forms of the same thing and are
    equivalent.
  • E mc2
  • E is energy in joules,
  • m is mass in kg,
  • c is the speed of light in vacuum 3.00x108 m/s

71
example
  • What is the amount of energy in one kilogram of
    mass?
  • Kilogram is very big unit of mass in the
    reference of mass-energy conversion.
  • Universal mass unit (u) is used
  • 1 u 9.31 x 102 MeV

72
example
  • According to the chart, the energy equivalent of
    the rest mass of a proton is approximately
  • 9.4 x 102 MeV
  • 1.9 x 103 MeV
  • 9.0 x 1016 MeV
  • 6.4 x 1018 MeV

73
example
  • Approximately how much energy would be generated
    if the mass in a nucleus of an atom of were
    converted to energy? 
  • The mass of is 2.0 atomic mass units.
  •   3.2 x 10-10 J
  •   1.5 x 10-10 J
  •   9.3 x 102 MeV
  •   1.9 x 103 MeV

74
question
  • Which particle would generate the greatest amount
    of energy if its entire mass were converted into
    energy?
  • electron
  • proton
  • alpha particle
  • neutron

75
example
  • How much energy would be generated if a 1.0
    x10-3-kilogram mass were completely converted to
    energy?
  •   9.3 x 10-1  MeV
  •   9.3 x 102  MeV
  •   9.0 x 1013  J
  •   9.0 x 1016  J

76
  • The graph represents the relationship between
    mass and its energy equivalent.  The slope of the
    graph represents
  • the electrostatic constant
  • gravitational field strength
  • the speed of light squared
  • Planck's constant

77
example
  • If a deuterium nucleus has a mass of 1.53 10-3
    universal mass units less than its components,
    this mass represents an energy of
  • 1.38 MeV
  • 1.42 MeV
  • 1.53 MeV
  • 3.16 MeV

78
example
  • The light of the "alpha line" in the Balmer
    series of the hydrogen spectrum has a wavelength
    of 6.58 10-7 meter. The energy of an "alpha
    line" photon is approximately
  • 6.63 10-34 J
  • 3.0 108 J
  • 3.02 10-19 J
  • 4.54 1013 J

79
example
  • The alpha line in the Balmer series of the
    hydrogen spectrum consists of light having a
    wavelength of 6.56 x 10-7 meter.
  • Calculate the frequency of this light.
  • Determine the energy in joules of a photon of
    this light.
  • Determine the energy in electronvolts of a photon
    of this light.

80
example
  • The energy equivalent of the rest mass of an
    electron is approximately
  • 5.1 105 J
  • 8.2 10-14 J
  • 2.7 10-22 J
  • 8.5 10-28 J

81
Nuclear mass and energy
  • According to Einsteins mass-energy equation, any
    change in energy results in an equivalent change
    in mass. Mass-energy is conserved at all levels
    from cosmic to subatomic.
  • In chemical reactions, if energy is released,
    then the total mass must be decreased. If energy
    is absorbed, then the total mass must be
    increased. However, the change of mass is too
    small to be measured.

82
  • In nuclear reaction, the changes in energy
    relative to the masses involved are much larger,
    the corresponding change in mass can be measured.
  • Example
  • total mass of two protons and two neutrons is
    2(1.0073 u 1.0087 u) 4.0320 u
  • The mass of a helium-4 is 4.0016 u
  • The mass of the nucleus is less than its
    components. This is true for every nucleus, with
    the exception for hydrogen-1, which has only one
    nucleon.

83
Nuclear fission and fusion
  • Nuclear fission is a nuclear reaction in which
    the nucleus of an atom splits into smaller parts
    (lighter nuclei). Fission of heavy elements is an
    exothermic reaction which can release large
    amounts of energy both as electromagnetic
    radiation and as kinetic energy of the fragments
    (heating the bulk material where fission takes
    place).
  • Nuclear fusion is the process by which two or
    more atomic nuclei join together, or "fuse", to
    form a single heavier nucleus. This is usually
    accompanied by the release or absorption of large
    quantities of energy. The fusion of two nuclei
    with lower masses than iron (which, along with
    nickel, has the largest binding energy per
    nucleon) generally releases energy while the
    fusion of nuclei heavier than iron absorbs energy
  • ..\..\RealPlayer Downloads\Fission And Fusion.flv

84
example
  • If a deuterium nucleus has a mass of 1.53 10-3
    universal mass units less than its components,
    this mass represents an energy of _______________
    MeV.

85
  • A tritium nucleus consists of one proton and two
    neutrons and has a total mass of 3.0170 atomic
    mass units.  What is the mass defect of the
    tritium nucleus?
  • 0.0014 u
  • 0.0077 u
  • 1.0010 u
  • 2.0160 u

86
Studying atomic nuclei
  • The structure of the atomic nucleus and the
    nature of matter have been investigated using
    particle accelerators.
  • Particle accelerators use electric and magnetic
    fields to increase the kinetic energies of
    charged particles, such as electrons and protons,
    and project them at speeds near the speed of
    light.
  • Collisions between the high speed particles and
    atomic nuclei may disrupt the nuclei and release
    new particles.

87
The standard model of particle physics -
objectives
  1. State the standard model of particle physics
  2. Describe the fundamental forces in nature
  3. Classify subatomic particles

88
Standard model of particle physics
..\..\RealPlayer Downloads\CERN- The Standard
Model Of Particle Physics.flv
  • The Standard Model of particle physics
    (formulated in the 1970s) describes the universe
    in terms of Matter (fermions - 24) and
    Force (bosons - 4).
  • Unlike the force-carrying particles, the matter
    particles have associated antimatter particles,
    such as the antielectron (also called positron)
    and antiquarks. So there are together 24 fermions.

89
The fundamental forces in nature
  • There are four known forces. Two of these forces
    are only seen in atomic nuclei or other subatomic
    particles. Aside from gravity, all the
    macroscopically observable forces such as
    friction pressure as well as electrical
    magnetic interaction are due to electromagnetic
    force.
  • Gravitational
  • Electromagnetic
  • strong nuclear
  • Weak nuclear
  • ..\..\RealPlayer Downloads\The Weak and Strong
    Nuclear Forces (9 of 15).flv
  • The weak nuclear force is another very
    short-range nuclear force that causes
    transformation of protons to neutrons and
    vice-versa, along with other radioactive (gives
    off photons and other particles) phenomena.

90
  • The Standard Model describe the force between two
    particles in terms of the exchange of virtual
    force carrier particles between them.

force Relative strength range Force carrier mass charge
Strong nuclear 1038 10-15 m gluon 0 0
Electro- Magnetic 1036 1/r2 photon 0 0
Weak nuclear 1025 10-18 m W boson W boson Z boson 80.6 GeV 80.6 GeV 91.2 GeV e -e 0
gravitational 1 1/r2 graviton 0 0
91
GRAVITY
Gravitation is a force of attraction that acts
between each and every particle in the Universe.
It is the weakest of the four fundamental forces.
It is always attractive, never repulsive. It
pulls matter together, causes you to have a
weight, apples to fall from trees, keeps the Moon
in its orbit around the Earth, the planets
confined in their orbits around the Sun, and
binds together galaxies in clusters.

92
THE ELECTROMAGNETIC FORCE
  • The electromagnetic force determines the ways in
    which electrically charged particles interact
    with each other and also with magnetic fields.
    This force can be attractive or repulsive.
  • This force holds the atoms together.
  • This force also governs the emission and
    absorption of light and other forms of
    electromagnetic radiation.

93
THE STRONG NUCLEAR FORCE
  • The strong nuclear force binds together the
    protons and neutrons that comprise an atomic
    nucleus and prevents the mutual repulsion between
    positively charged protons from causing them to
    fly apart.
  • The strong nuclear force interaction is the
    underlying source of the vast quantities of
    energy that are liberated by the nuclear
    reactions that power the stars.

94
THE WEAK NUCLEAR FORCE
  • The weak nuclear force causes the radioactive
    decay of certain particular atomic nuclei. In
    particular, this force governs the process called
    beta decay whereby a neutron breaks up
    spontaneously into a proton, and electron and an
    antineutrino.

95
LONG-RANGE and SHORT-RANGE FORCES
  • The strong and weak nuclear interactions are
    effective only over extremely short distances.
    The range of strong force is about 10-15 meters
    and that of the weak force is 10-18 meters.
  • In contrast, the electromagnetic and
    gravitational interactions are long-range forces,
    their strengths being inversely proportional to
    the square of distance.

96
Force carriers
  • According to modern quantum theories, the various
    fundamental forces are conveyed between real
    particles by means of virtual particles. The
    force-carrying particles (which are known as
    gauge bosons) for each of the forces are as
    follows
  • electromagnetic force - photons
  • weak nuclear interaction - very massive 'W' and
    'Z' bosons
  • strong nuclear interaction - gluons.
  • gravitation - graviton.

97
The fundamental forces
force Relative strength Range of force Force carrier mass charge
Strong (nuclear) 1 10-15m gluon 0 0
electromagnetic 10-2 1/r2 photon 0 0
weak 10-13 lt 10-18m W boson W boson Z boson 80.6 GeV 80.6 GeV 91.2 GeV e -e 0
gravitational 10-38 1/r2 graviton 0 0
98
example
  1. Which force is responsible for a neutron decaying
    into a proton?
  2. Which force bonds quarks together into particles
    like protons and neutrons?
  3. Which force governs the motion of an apple
    falling from a tree?

99
  • What are you made of? What forces hold you
    together?

100
Sub-Atomic Particles
  • Although the Proton, Neutron and Electron have
    been considered the fundamental particles of an
    atom, recent discoveries from experiments in
    atomic accelerators have shown that there are
    actually 12 fundamental particles (with 12
    antiparticles). Protons and neutrons are no
    longer considered fundamental particles in this
    sub-atomic classification.

101
The fundamental particles are classified into two
classes quarks and leptons
102
Hadrons and lepton
  • Particles can be classified according to the
    types of interactions they have with other
    particles.
  • A particle that interacts through the strong
    nuclear force, as well as the electromagnetic,
    weak and gravitational forces is called a hadron.
  • A particle that interacts through the
    electromagnetic, weak and gravitational forces,
    but not the strong nuclear force, is called a
    lepton.

103
Hadrons baryons mesons
  • Hadrons group can be subdivided into baryons and
    mesons.
  • Baryons are made of three quarks, the charges on
    a baryon can be 0, 1, or -1
  • examples of baryons are neutrons, protons.
  • The term "baryon" is derived from the Greek ßa???
    (barys), meaning "heavy.
  • Mesons are made a quark-antiquark pair, mesons is
    a particle of intermediate mass.

104
  • All hadrons are constructed of quarks.

A baryon is made up of 3 quarks, for example A
proton consists of up, up, down quarks A neutron
consists of up, down, down quarks When quarks
combine to form baryons, their charges add
algebraically to a total of 0, 1, -1.
105
example
  • Baryons may have charges of
  • 1e and 4/3 e
  • 2e and 3e
  • -1e and 1e
  • -2e and - e

106
question
  • Protons and neutrons are examples of
  • positrons
  • baryons
  • mesons
  • quarks

107
What are the Leptons?
  • A lepton has a mass much less than that of a
    proton, the lepton classification of sub-atomic
    particles consists of 6 fundamental particles
  • Electron
  • Muon
  • Tau
  • Electron Neutrino
  • Muon Neutrino
  • Tau Neutrino
  • The reference tables give the names, symbols and
    charges of the six members of the lepton family.

108
Electron, Muon and Tau Leptons
  • The Electron remains a fundamental particle, as
    if was in the Atomic Theory. It has an electrical
    charge of (-1) and plays an active role in
    chemical reactions.
  • The Muon is primarily a result of a high-energy
    collision in an atomic accelerator. The Muon is
    similar to an Electron, only heavier.
  • The Tau particle is similar to a Muon, only
    heavier yet.
  • Muon and Tau particles are unstable and exist in
    nature for a very short time.

109
Neutrinos
  • Neutrinos are small and have no electrical
    charge. This makes them extremely difficult to
    detect. They can possess a large amount of energy
    and the very rare times they do collide with
    another particle, that energy can be released.
  • There are 3 types of neutrinos
  • Electron Neutrino, which has no charge and is
    extremely difficult to detect
  • Muon Neutrino, which is created when some atomic
    particles decay
  • Tau Neutrino, which is heavier than the Muon
    Neutrino.

110
Quarks
  • Another group of sub-atomic particles are the
    Quarks. Just like their name, they exhibit
    unusual characteristics. There are 6 fundamental
    particles among the Quarks are
  • Up and Down Quarks
  • Charm, Strange, Top and Bottom Quarks
  • Other particles are made up of combination of
    Quarks.
  • The reference table gives the names, symbols, and
    charges of the six quarks.

111
Up and Down Quarks
  • The Up Quark has an electrical charge of (2/3).
    The Down Quark has an electrical charge of
    (-1/3).
  • The Proton is made up of  two Up Quarks and one
    Down Quark. The electrical charge of the proton
    is then (2/3) (2/3) (-1/3) (1).
  • The Neutron is made up of one Up Quark and two
    Down Quarks. The resulting electrical charge of
    the Neutron is (2/3) (-1/3) (-1/3) (0).

112
Charm, Strange, Top and Bottom Quarks
  • The Charm Quark has the same electrical charge as
    the Up Quark but is heavier. The Top Quark is
    then heavier than the Charm.
  • The Strange Quark has the same electrical charge
    as the Down Quark but is heavier. The Bottom
    Quark is heavier than the Strange.

113
baryons
mesons
6 types
3 quarks
quark and antiquark
6 types of quarks
114
antiparticle
  • An antiparticle is associated with each particle.
  • An antiparticle is a particle having mass,
    lifetime, and spin identical to the associated
    particle, but with charge of opposite sign (if
    charged) and magnetic moment reversed in sign. An
    antiparticle is denoted by a bar over the symbol
    of the particle.
  • Example p, stands for antiproton, which can be
    described as a stable baryon carrying a unit
    negative charge, but having the same mass as a
    proton.

115
  • A positron (e) is a particle whose mass is equal
    to the mass of the electron and whose positive
    electric charge is equal in magnitude to the
    negative charge of the electron.
  • Positron is the antiparticle of electron (e).
  • The antineutron (n) has the same mass as the
    neutron and is also electrically neutral. However
    the magnetic moment and spin of the antineutron
    are in the same direction, whereas, the magnetic
    moment and spin of the neutron are in opposite
    directions.
  • Antiparticle for a neutrino is identical to the
    neutrino except for their direction of spin.

116
quarks
antiquarks
leptons
antileptons
6
6
6
6
There are total of 24 basic particles
117
antimatter
  • Antimatter is material consisting of atoms that
    are composed of antiprotons, antineutrons, and
    positrons.

118
example
  • The subatomic particles that make up both protons
    and neutrons are known as
  • electrons
  • nuclides
  • positrons
  • quarks

119
example
  • According to the Standard Model, a proton is
    constructed of two up quarks and one down quark
    (uud), and a neutron is constructed of one up
    quark and two down quarks (udd). During beta
    decay, a neutron decays into a proton, an
    electron, and an electron antineutrino. During
    this process there is a conversion of a
  • u quark to a d quark
  • d quark to a meson
  • baryon to another baryon
  • lepton to another lepton

120
example
  • A lithium atom consists of 3 protons, 4 neutrons,
    and 3 electrons. This atom contains a total of
  • 9 quarks and 7 leptons
  • 12 quarks and 6 leptons
  • 14 quarks and 3 leptons
  • 21 quarks and 3 leptons

121
example
  • A top quark has an approximate charge of
  • -1.07 10-19 C
  • -2.40 10-19 C
  • 1.07 10-19 C
  • 2.40 10-19 C

122
example
  • Compared to a proton, an alpha particle has
  • Hint An alpha particle is a helium nucleus.
  • the same mass and twice the charge
  • twice the mass and the same charge
  • twice the mass and four times the charge
  • four times the mass and twice the charge

123
example
  • What is the charge-to-mass ratio of an electron?

124
example
  • During the process of beta (ß-) emission, a
    neutron in the nucleus of an atom is converted
    into a proton, an electron, an electron
    antineutrino, and energy. 
  • neutron  proton electron electron
    antineutrino energy 
  • Based on conservation laws, how does the mass of
    the neutron compare to the mass of the proton?
  • The mass of the neutron is greater than the mass
    of the proton.
  • The mass of the proton is greater than the mass
    of the neutron.
  • The masses of the proton and the neutron are the
    same.
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