Nuclear Chemistry

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Nuclear Chemistry
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10.1 Radioactivity

• Radioactivity process in which an atomic nucleus
  emits charged particles and energy

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• Radioisotope any atom containing an unstable
  nucleus

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During nuclear decay, atoms of one element can
change into atoms of a different element
altogether Uranium 238 decays into Thorium
234 (also a radioisotope)

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• Nuclear Radiation charged particles and energy
  that are emitted from the nuclei of radioisotopes
• Common nuclear radiation types
• alpha particle
• beta particle
• gamma rays

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Alpha Decay

• Alpha Particle (?) a positively charged particle
  made up of 2 protons and 2 neutrons (the SAME as
  a HELIUM NUCLEUS)
• Common symbol ?

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• Example of alpha decay of uranium 238

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Dangers of Nuclear Radiation

• Least penetrating type of nuclear radiation, can
  be stopped by sheet of paper or clothing

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Beta Decay

• Beta Particle (?) an electron emitted by an
  unstable nucleus
• Written as ?
• Assigned atomic of -1 mass of 0 (zero)
• How can a nucleus (which is positive), emit a
  negatively charged particle?

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• During beta decay, a neutron
• decomposes into a proton and an e-

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• Proton stays trapped in the nucleus, e- released

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• Example of beta decay of thorium 234

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• Product isotope has 1 proton more and 1 neutron
  fewer than the reactant isotope
• Mass number of the isotopes are equal because the
  emitted beta particle has essentially NO MASS
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• Beta particles pass through paper, but stopped by
  thin sheet of metal

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Gamma Decay

• Gamma Ray (?) a penetrating ray of energy
  emitted by an unstable nucleus

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Gamma Decay

• NO mass and NO charge
•  During Gamma Decay
• Atomic number and mass number of the atom remains
  the same
• Energy of nucleus decreases

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• Gamma decay often accompanied by alpha or beta
  decay
• Example of thorium 234 emitting both beta
  particles and gamma rays as it decays
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•  

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• Gamma rays much more penetrating takes several
  centimeters of lead or several meters of concrete
  to stop gamma radiation

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Effects of Nuclear Radiation

• Background Radiation nuclear radiation that
  occurs naturally in the environment

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• When nuclear radiation exceeds background levels,
  it can damage the cells and tissues of your body

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Effects of Nuclear Radiation

• Nuclear radiation can ionize atoms (when cells
  are exposed to nuclear radiation, the bonds
  holding together proteins and DNA molecules may
  break ?cells may no longer function properly)

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Effects of Nuclear Radiation

• ?, ?, and ? are all forms of ionizing radiation
• The extent of the damage of external nuclear
  radiation is dependent on the penetrating power
  of the radiation

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• Beta particles cause more damage than alpha
  particles, but less than gamma rays
• Gamma rays can penetrate deeply into the human
  body, potentially exposing all organs to
  ionization damage

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Detecting Nuclear Radiation

• Although you cant see, hear, or feel the
  radioactivity around you, scientific instruments
  can measure nuclear radiation
• Geiger Counters
• Film Badges
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10.2 ? Rates of Nuclear Decay
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Nuclear Decay

• By studying the radioactive nuclei of an object
  we can determine how old the object is.
• Because most materials contain at least trace
  amounts of radioisotopes, scientists can estimate
  how old they are based on rates of nuclear decay.

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Half-Life

• Half-life the time required for one half of a
  sample of a radioisotope to decay
• After one half-life, half of the atoms in a
  radioactive sample have decayed, while the other
  half remain unchanged
• After two half-lives, half of the remaining have
  decays, leaving one quarter of the original
  sample unchanged

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Half-Life Example

• Iodine Half-life 8.07 days
• After one half-life (8.07 days) half of the
  original sample remains
• After 2 half-lives (16.14 days) one quarter of
  the original remains
• After 3 half-lives (24.21 days) one half of one
  quarter remains, or 1/8 (one eighth)
• and so on

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Half-Lives Vary

• Half-lives can vary from fractions of a second to
  billions of years
• Unlike chemical reaction rates, which vary with
  the conditions of a reaction, nuclear decay rates
  are constant!!!

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Radioactive Dating

• Method used for determining the age of objects
  using the half-lives of Carbon 14
• Radiocarbon dating determining the age of an
  object by comparing its carbon-14 levels with
  carbon-14 levels in the atmosphere. 

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Radioactive Dating

• Carbon-14 has a half-life of 5,730 years.
• Carbon-14 is formed in the upper atmosphere when
  neutrons produced by cosmic rays collide with
  nitrogen-14 atoms.
• The radioactive carbon-14 undergoes beta decay to
  form nitrogen-14.

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Using Carbon-14 to Date

• Living organisms absorb the carbon (CO2) from the
  atmosphere, but when they die they stop absorbing
  it and the levels do not change.
• From this point levels start to decrease as the
  radioactive carbon decays.
• The levels in the object are then compared with
  levels in the atmosphere. 

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Example if an object has half the amount of
carbon-14 in it as in the atmosphere, then we
know the object is about 5, 730 years old (which
is one half-life for carbon-14)  
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Carbon-14 Dating

• Carbon-14 or radiocarbon dating can be used to
  date any carbon-containing object less than
  50,000 years old.  
• After this point, there is too little carbon-14
  left to be measurable  
• Objects older than this use radioisotopes with
  longer half-lives  
• The older the object the lower the levels of
  radioisotopes present  

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10.3 ?Artificial Transmutation
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Transmutation

• Transmutation the conversion of atoms of one
  element to atoms of another.  
• It involves a nuclear change, not a chemical
  change.  
• Transmutations can either occur naturally
  (nuclear decay) or artificially.  
• Scientists can perform artificial transmutations
  by bombarding atomic nuclei with high-energy
  particles such as protons, neutrons, or alpha
  particles.  

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Transuranium Elements

• Transuranium Elements Elements with atomic
  numbers greater than 92 (uranium)  
• All transuranium elements are radioactive and
  generally not found in nature  
• Scientists can create a transuranium element by
  the artificial transmutation of a lighter element
   
• Useful transuranium elements  
• Americium-241 used in smoke detectors  
• Plutonium-238 energy source for space probes

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Particle Accelerators

• Sometimes transmutations will not occur unless
  the bombarding particles are moving at extremely
  high speeds.  
• To achieve these high speeds scientists use
  particle accelerators.  

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Particle Accelerator

• These accelerators move charged particles at
  speeds very close to the speed of light
• The particles are then guided toward a target,
  where they collide with atomic nuclei and
  transmutations are allowed to occur
• These collisions have also lead to the discovery
  of more subatomic particles
• Quarks protons and neutrons are made up of these
  even smaller particles

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Large Hadron Collider (LHC)
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10.4 ? Fission Fusion
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Question

• What holds the nucleus together?
• Its full of positive particles, so why dont
  they push each other away?
• What keeps the protons and neutrons together?
• Clearly, there must be an attractive force that
  binds the particles

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Answer

• Strong Nuclear Force the attractive force that
  binds protons and neutrons together in the
  nucleus
• Over very short distances, the strong nuclear
  force is much greater than the electric forces
  among protons

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Forces in the Atom
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Electric Force

• Question What determines the strength of the
  electric force?
• Answer The number of protons

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Electric Force

• The greater the number of protons, the greater is
  the electric force that repels the protons
• Larger nuclei have a stronger repulsive force
  than a smaller nuclei
• As a result, the nucleus will become unstable (or
  radioactive) when the strong nuclear forces cant
  overcome the repulsive electric forces among
  protons.

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Nucleus Size Radioactivity

• Because of the size issue, there is a point
  beyond which all elements are radioactive.
• Once they become large enough, the repulsive
  forces overcome. This occurs with all nuclei
  with 83 or more protons.
• Therefore, all elements with an atomic number
  greater than 83 are radioactive!

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Fission

• FISSION the splitting of an atomic nucleus into
  two smaller parts
• In nuclear fission, tremendous amounts of energy
  can be produced from very small amounts of mass

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Converting Mass into Energy

• During a fission reaction, some of the mass of
  the reactants is lost!
• The Law of Conservation of Mass says this is
  illegal, highly illegal!
• This lost mass is converted into energy!

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Converting Mass into Energy

• Since we bent the law a littlewe use a revised
  version of the law Law of Conservation of Mass
  and Energy
• It basically says The total amount of mass and
  energy remains constant!!!

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E mc2

• 30 years before the discovery of fission, Albert
  Einstein introduced the mass-energy equation.  
• Emc2describes the relationship between mass and
  energy
• E energy
• m mass
• c the speed of light (3.0 x 108m/s) 
• It shows that the conversion of a small amount of
  mass releases an ENORMOUSamount of energy. 

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Lots of Energy!!!

• Example the explosion of the first atomic bomb
  contained 5kg of plutonium, but created an
  explosion equivalent to18, 600 tons of TNT!!!  
• So, since we bent the law a little, just a
  little, we use a revised version of the law
• This law is referred to as the Law of
  Conservation of mass and energy.
• It basically says
• THE TOTAL AMOUNT OF MASS AND ENERGY REMAINS
  CONSTANT!

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Chain Reaction

• Nuclear fission reactions act like rumors being
  spread throughout school
• One person tells a few friends, they tell a few
  friends, and on and on
• During a fission reaction each reactant nucleus
  splits into 2 smaller nuclei and releases 2-3
  neutrons.
• If one of these neutrons is absorbed by another
  nucleus, fission can result again, releasing more
  neutrons.

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Triggering a Chain Reaction

• CHAIN REACTION neutrons released during the
  splitting of an initial nucleus trigger a series
  of nuclear fissions.
• Uncontrolled chain reactions occur when each
  released neutron is free to cause other fissions

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Chain Reaction
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Chain Reaction

• Nuclear weapons are designed to produce
  uncontrolled chain reactions
• In order for a chain reaction to keep going, the
  nucleus that splits needs to produce one neutron
  that causes the fission of another nucleus
• The material reacting uncontrolled needs to have
  a critical mass.
• CRITICAL MASS the smallest possible mass of a
  fissionable material that can sustain a chain
  reaction.

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Fusion

• Another type of nuclear reaction can release huge
  amounts of energy is fusion
• FUSION a process in which the nuclei of two
  atoms combine to form a larger nucleus.
• Just like fission, a small fraction of the mass
  is converted into energy

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Example of Fusion

• The sun and stars are powered by the fusion of
  hydrogen into helium
• Fusion requires extremely high temperatures where
  matter exists as plasma.
• This is a problem for scientists wanting to use
  fusion for an energy source
• They cannot get high enough temperatures and have
  trouble containing plasma here on Earth

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Fusion in the Core