Nuclear Chemistry

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Nuclear Chemistry
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Chemical vs. Nuclear

• Occurs when nuclei emit particles and/or rays
• Atoms of one element are converted into another
  element
• May involve protons, neutrons, or electrons
• Have large energy changes
• Reaction rates are not affected

• Occurs when bonds are broken and formed
• Atoms remain unchanged, but the may be rearranged
• Involve only valence electrons
• Have small energy changes
• Reaction rates are influenced by temperature,
  pressure, concentration, and catalysts

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Nuclear Forces

• Nucleons- the protons and neutrons of the nucleus
• Strong Force- the force that holds protons and
  neutrons together in the nucleus.

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Nucleus

• Protons and Neutrons can be broken down further
  into quarks.
• When protons and neutrons come together to form
  the nucleus, energy is released called the
  nuclear binding energy.

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Nucleus, cont

• When parts of the atom combine, the total mass is
  less than the beginning mass. This is the Mass
  Defect.
• The mass defect is the result of mass being
  converted to energy during the process.

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Nucleus, cont

• Einsteins equation E mc2 can be used to
  determine the binding energy for an atom.

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Stability

• Proton Neutron ratio
• 1 or 1.5 ratio is stable
• If atoms have atomic numbers larger than 83 or
  mass numbers greater than 209 they are unstable.
• Remember proton the strong force has to do with
  the proton - neutron relationship.

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Types of Radiation

• Unstable nuclei emit radiation to attain more
  stable atomic configurations in a process called
  radioactive decay.
• During radioactive decay, unstable atoms lose
  energy by emitting one of several types of
  radiation.

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Types of Radiation

• The three most common types of radiation are
  alpha (a), beta (ß), and gamma (?).

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Alpha

• An alpha particle (a) has the same composition as
  a helium nucleustwo protons and two neutronsand
  is therefore given the symbol 42 He .
• The charge of an alpha particle is 2 due to the
  presence of the two protons.

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Alpha

• alpha particles are relatively slow-moving
  compared with other types of radiation.
• Thus, alpha particles are not very penetratinga
  single sheet of paper stops alpha particles.

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Beta

• A beta particle (?) is a very-fast moving
  electron that has been emitted from a neutron of
  an unstable nucleus.
• Beta particles are represented by the symbol
  0-1?.
• The 1 subscript denotes the negative charge of
  the particle.

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Beta

• Because beta particles are both lightweight and
  fast moving, they have greater penetrating power
  than alpha particles.
• A thin metal foil is required to stop beta
  particles.

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Gamma

• Gamma rays (?) are high-energy (short wavelength)
  electromagnetic radiation. They are denoted by
  the symbol 00?
• The emission of gamma rays does not change the
  atomic number or mass number of a nucleus.
• Gamma rays almost always accompany alpha and beta
  radiation.

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Gamma

• Gamma rays are high energy radiation
• They can only be blocked by lead

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Writing Nuclear Reactions

• When writing nuclear reactions, you must remember
  the Law of Conservation of Matter
• What you start with has to equal what you end
  with
• You also have to remember how to write formulas
  for isotopes

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Nuclear Reactions

• Write the reaction for radium 226 converting into
  radon 222
• Radium 226 is 22688Ra
• Radon 222 is 22286Rn
• Write the equation
• 22688Ra ? 22286Rn
• Now you must find what is missing
• 22688Ra ? 22286Rn 42He

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Nuclear Reactions

• Write the reaction of carbon-14 decaying into
  nitrogen 14
• 146C ? 147N
• Now see whats missing
• Only add to the product side
• 146C ? 147N 0-1?

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Nuclear Reactions

• Write the reaction of uranim-238 undergoing alpha
  and gamma decay
• 23892U ? 42He 00?
• Now put whats left
• 23892U ? 42He 00? 23490Th

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Half Life

• Half life - time required for ½ of a radioisotope
  to decay
• For example
• You have 100 g of an isotope. How much is left
  after 1 half life?
• 50g
• How much will be left after 2 half lifes?
• 25g

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Carbon -14 Dating

• A process of using radioactive decay of C-14 to
  measure the age of artifacts/remains of once
  living organisms.
• C-14 undergoes beta decay to form N-14

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Fission and Fusion

• Fission splitting the nucleus into fragments
• Releases large amounts of energy
• Nuclear power plants use fission to generate power

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Fission and Fusion

• Fusion combining of atomic nuclei
• Release large amounts of energy
• Require extremely high temperatures
• The lowest temperature possible is 40,000,000 K
• Known to occur on the sun

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Nuclear Waste

• Nuclear waste is spent fuel that can no longer
  be used to create energy.
• This material is still radioactive and must be
  disposed of with care.

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Units for Radioactivity

• Curie (C) radioactive decay
• Rad (rad) energy absorbed by ionizing radiation
• Rem (rem) biological effect of the absorbed
  dose in humans.