Nuclear chemistry

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Nuclear chemistry
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Radioactivity

• Atoms tend to attain stable electron
  configurations
• All atoms like to be happy ? (balanced or
  neutral)
• A nuclear reaction deals with reactions in which
  the nuclei of unstable isotopes gain stability by
  undergoing changes-radioisotopes
• These reactions are not effected by temperature,
  pressure, or a catalyst (speeds up or slows down
  reactions)
• These atoms cannot be slowed down, sped up or
  turned off

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Radioactivity continued

• The presence of too many or too few neutrons
  relative to the number of protons
• Leads to an unstable nucleus
• An unstable nucleus loses energy by emitting
  radiation- called radioactive decay
• Eventually, unstable radioisotopes of one element
  are transformed into stable isotopes of a
  different element
• Its spontaneous- does not require energy
• Creates different types of radiation

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Types of RadiationAlpha Radiation

• Alpha particle- consists of helium nuclei that
  have been emitted (released) from a radioactive
  source.
• Atomic number decrease by 2 and mass by 4
• Carry a positive charge
• Tend to not travel far (large mass and charge)
• Can be stopped by paper or skin
• In nuclear equations- written as 4 2He or a
• 238 92U ? 234 90Th 4 2He

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Types of radiationBata Radiation

• Beta particle- fast moving electrons formed by
  the decomposition of a neutron in an atom
• In decomp. The new proton stays in nucleus, but
  releases an electron
• Carry a negative charge
• Have MUCH less charge and mass than alpha
  particle
• More penetrating- can be stopped by aluminum foil
  or thin pieces of wood
• In nuclear equations- 1 0n?1 1H 0 -1e

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Types of radiation Gamma radiation

• high energy electromagnetic radiation given off
  by a radio isotope
• Often omitted along with alpha or beta particles
• No mass or electric charge
• Do NOT alter atomic number or mass number
• Nuclear equationsame as alpha or beta gamma ray

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Types of radiationX-rays

• Behave essentially the same as gamma rays but
  origin is different
• They ARE NOT emitted during radioactive decay
• Are produced as excited electrons in certain
  metals when they lose energy
• Can pass easily through paper and wood
• Cant be stopped completely
• Several centimeters of lead or several meters of
  concrete

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Types of Radiation
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Nuclear stability and decay

• A nucleus may be unstable for several reasons
• Some nuclei have too MANY neutrons relative to
  the number of protons
• These nuclei decay by turning a neutron into a
  proton and by emitting a beta particle
• 1 0n ? 1 1H 0 -1e
• Other nuclei are unstable because of too FEW
  neutrons relative to the number of protons

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Nuclear stability and decay continued

• These become stable by converting a proton into a
  neutron
• In this case an electron is captured!
• 59 28Ni 0 -1e ? 59 27Co How many protons?
  neutrons
• 37 18Ar 0 -1e ? 37 17Cl How many protons?
  Neutrons
• Positrons
• A particle with a mass of an electron but it has
  a POSITIVE charge
• May be emitted as a proton changes into a neutron

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Positrons continued

• Examples
• 8 5B ? 8 4Be 0 1e
• 15 8O ? 15 7N 0 1e
• All nuclei with an atomic number greater than 83
  are radioactive- too many neutrons or too many
  protons to be stable- they all undergo decay.
• Most of them emit alpha particles- this helps
  increase the proton/neutron ratio

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Particle comparison

• particle

• symbol

• Alpha
• Beta
• Gamma
• Positron
• proton

• 4 2He
• 0 -1e
• 0 0 ?
• 0 1e
• 1 1H

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Half Life

• Time required for one-half of the nuclei of a
  radioisotope to decay into products
• After one half life, half of the original sample
  will remain
• Every radioisotope has a unique half life
• Half life may be short- fraction of a second or
  long- billions of years
• Ex Uranium-238 has an approximate half life of
  billions of years

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Half life problem

• Imagine winning a 1000 prize but the conditions
  of the award require that half of the remainder
  of the prize is spent each month. After how many
  months would you be left with less then a 1?
  What is the half life of this prize?

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Practice problems

• If the half life of a radioactive material is 8
  yrs, how many years will it take for one half of
  the original amount of material to decay?
• Manganese-56 has a half life of 2.6hrs. What is
  the mass of manganese-56 in a 1.0mg sample of the
  isotope at the end of 10.4hrs?
• Start by figuring out how many half life's there
  will be.

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Transmutation Reactions

• Transmutation- the conversion of an atom of one
  element to an atom of another element
• Occurs during radioactive decay
• Occurs when high energy particles bombard the
  nucleus
• Transuranium elements- elements on the periodic
  table with atomic numbers 92 and above.
• They all undergo transmutation
• All are man made
• All are radioactive

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Nuclear fission

• When nuclei are split apart because they have
  been bombarded with neutrons.
• When fission occurs it creates smaller elements
• It also send more neutrons out that creates a
  chain reaction.
• Unleashes and ENOURMOUS amount of energy
• This is how nuclear power plants work
• Occurs in nuclear reactors
• Can be controlled

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Nuclear fusion

• When nuclei of smaller elements combine to
  produce nuclei of greater mass
• Hydrogen join to create helium
• Fusion only takes place in stars (our Sun)- it
  requires a HUGE amount of heat and pressure
• Fusion releases more energy then fission