The Nucleus of the Atom

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The Nucleus of the Atom

• Chapter 12

Great Idea Nuclear energy depends on the
conversion of mass into energy
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Empty Space, Explosive Energy

• Empty space
• If a nucleus is the size of a baseball, the
  electrons are about 15 miles away.
• Relation of atom to nucleus
• What goes on in the nucleus has almost nothing to
  do with the atoms chemistry, and vice versa
• The energies available in the nucleus are much
  greater than those available among electrons
• Mass and energy Emc2
• In the US, each person uses about 10,000 kwh
  energy each year. How much mass is it
  corresponding to?

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The Organization of the Nucleus

• Atomic nuclei sometimes break into small
  fragments.
• Nucleus is made up of smaller pieces
• Protons and Neutrons
• Particles Mass Charge
• Proton 1 1
• Neutron 1 0
• Electron 1/1860 -1
• (mass 1 1.67x10-27kg charge 1 1.6x10-19C)
• Electrons give an atom its size, and nucleus
  gives atom its mass

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Atomic Numbers, Isotopes, and the Mass Number

• Atomic number
• Number of protons in nucleus.
• Defines chemical behavior
• Isotopes
• Elements with same number of protons but
  different numbers of neutrons.
• Example C-12, C-13, C-14
• About 2000 isotopes have been documented
• Mass number
• Total protons and neutrons

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(Continue)

• Example 12-1
• Inside the atom
• 1. We find an atom with 9 protons and 8 neutrons
  in its nucleus and 10 electrons in orbit.
• a. What element is it? (Fluorine)
• b. What is its mass?
• c. What is the electric charge?
• d. How is it possible that the number of protons
  and electrons are different?
• Example 12-2
• A heavy element
• 2. How many protons, neutrons, and electrons are
  contained in the atoms when it has a
  charge of 2?

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Periodic Table
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(Continue)

• Problems Page 259
• 1. Use the periodic table to identify the
  element, atomic number, mass number, and
  electrical charge of the following combinations
• a. 7 protons, 7 neutrons, 10 electrons
• b. 8 protons, 8 neutrons, 8 electrons
• 2. Us the periodic table to determine how many
  protons and neutrons are in each of the following
  atoms
• a. C-13
• b. Zn-66

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The Strong Force

• Strong force
• Force that holds nucleus together
• Operates only over very short distances
  characteristic of the size of nucleus
• Binding energy
• The mass of the nucleus is always slightly less
  than the sum of the masses of the protons and
  neutrons some of their mass is converted into
  the energy that binds them together

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What is Radioactive?

• Radioactivity or radioactive decay
• spontaneous release of energetic particles of the
  nuclei
• 99.999 of atoms in everyday surroundings are
  stable nuclei will never change
• Some kinds of nuclei are not stable U-238
• Radiation
• the emitted particles measured by Geiger counter

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The Kinds of Radioactive Decay

• Alpha Decay
• Release of Alpha particle
• Composed of 2 protons and 2 neutrons (same as the
  nucleus of a He-4)
• Reduces the mass and changes the chemical
  identity of decaying nucleus
• Alpha particles travels at very high speed when
  leaving parent nucleus, collisions, convert
  energy to heat. About half of Earths interior
  heat comes from this.
• Beta Decay
• Emission of electron
• Gamma Radiation
• Electromagnetic radiation

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Moving Down the Chart of the Isotopes
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Radiation and Health

• Why is nuclear radiation so dangerous?
• Alpha, beta, and Gamma radiations all carry a
  great deal of energy
• Ionization Stripping away an atoms electrons
• Great deal of radiation causes sickness or death
  Hiroshima and Nagasakis atomic bombs
• Long-term effects
• Cancer
• Birth defects

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Half-Life

• Half-life
• Average time for decay of ½ batch of radioactive
  isotopes
• Example 100 nuclei at beginning, half-life 20
  minutes.
• Wide range of half-lives
• U-222, half life a tiny fraction of a second
• U-238, half life in billions of years
• Half-life cannot be predicted but can be easily
  measured.

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Radiometric Dating

• Radiometric dating
• Determine the age of materials
• Depends on Measurement of half-life of
  radioactive materials
• Carbon-12 99
• Carbon-13 1
• Carbon-14 radioactive isotope
• no more than 1 in every trillion
• Half-life 5700 years
• Is about the same in all living things
• Stop taking in Carbon in any form from the time
  of death
• Geology
• when object is more than 50,000 years old
• Need longer half-lives
• Potassium-40 1.25 billion years
• Uranium-238 49 billion years

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Decay Chains

• Decay chains
• Series of decays
• Continues until stable isotope appears

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Indoor Radon

• Decay of Uranium-238
• Radon-222
• Can build up in well-insulated, tightly scaled
  buildings
• Expose to high radon levels is dangerous because
  each radon atom will undergo at least five more
  radioactive decay events in a few days.
• Test radon
• Increase ventilation
• www.epa.org/radon/pubs/citguide.html A Citizen's
  Guide to Radon The Guide to Protecting Yourself
  and Your Family From Radon 

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Nuclear Fission

• Fission
• Splitting of nucleus
• Chain reaction
• Critical mass minimum mass for a self-
  sustaining chain reaction

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(Continue)

• Nuclear Reactor
• Extracts energy from nuclear reaction
• Confine dangerous radioactive materials
• Meltdown
• Flow of water to fuel rod is interrupted,
  overheat cause the fuel rod to melt

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Fusion

• Fusion
• two hydrogen nuclei combine together
• Some mass converted into energy
• The nuclear reaction powers the sun and other
  stars

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Nuclear Weapons
The gun concept used in the Little Boy uranium
bomb design
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Nuclear Waste Management

• There are 131 temporary repositories located in
  39 different states
• Should we confine all nuclear waste in a single,
  remote, long-term site (Yucca Mountains in
  Nevada)?
• Supporters
• Opponents

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Homework

• Self-quiz of Chapter 12
• More Exercises
• Chapter 12 3-9, 11,12, 19-27, 29, 35,36,38-40