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Nuclear Chemistry• Nucleus is held together by “strong” or “nuclear”
forces. – Strongest forces in the universe
– Between like charges
– The closer the charged particles, the stronger the force
• Too many neutrons can get in the way of this force and make the nucleus unstable.
• “Neutron-Heavy” isotopes stabilize in two ways:– Emitting small amounts of radioactivity
– Flying apart with great amounts of energy
Spontaneous Radioactive Decay
• Nucleus spontaneously changes structure to reduce the number of neutrons and become more stable.– Alpha particle emission
– Beta particle emission
– Gamma ray emission
Alpha Decay
• Atomic number decreases by 2
• Element changes - transmutation
Beta Decay
-
• Atomic number INCREASES by 1
• Element changes - transmutation
Gamma Radiation
• Emission of gamma rays (γ)
• Very high energy light waves with high frequency
• Non-particulate in nature
• Mass is lost!!!
Half-Life• Time required for half an amount of isotope
to decay• Varies from fractions of a second to billions
of years
• Formula:
• Practice: If you have 10 Kg of radioactive Barium and the half-life is 13 days, how much barium will be left after 100 days?
Applications of Radioactivity• Smoke detectors
– Use americium
• Medicine– Imaging and analysis– Cancer treatment
• Determining the age of the earth– U-238 present in rocks slowly
decays to Pb-206– The age of the earth is:
4.5 billion years!!!
NUCLEAR FISSION• Nucleus of a radioactive element splits by
bombardment from an external source
• Simultaneous release of large amounts of energy, in the form of heat, light and sound – Exothermic Process!!
Nuclear FissionNeutron induced to U235
The sum of the masses of the resulting nuclei is about 0.1% less than the original mass
The “missing mass” is converted to energy according to E=mc2
Chain ReactionsThree neutrons are released and may:
• Cause another fission by colliding with a U235 nucleus. If enough neutrons are present a chain reaction will occur.
• Called the Critical Mass
• Each split released a large amount of ENERGY!
• Be absorbed in other material
• Get lost in the system
Destructive Fission Reactions• Chernobyl
• Atomic Bombs dropped on Japan
Nuclear Fission Power• Similar to Coal power
• Heat is generated by a fission reaction rather than from the burning of coal
• Benefits: cheaper after setup, uses very little fuel
• Drawbacks: can be dangerous if reaction is not controlled, creates radioactive waste
Nuclear Reactors• Control rods absorb
neutrons to control the rate of reaction.
• Nuclear subs use this technology so they do not have to transport gasoline or coal.
Nuclear Fusion• Multiple nuclei join together to form a heavier nucleus. • Releases of large amounts of energy.• The sun converts hydrogen to helium in a fusion reaction.
This is the source of most of our ENERGY
Fusion Power• Benefits: uses plentiful
hydrogen, creates very large amounts of energy
• Drawbacks: – requires massive amounts of
heat to start the reaction– Too little mass to create a
sustained reaction• Uses of fusion already:
– Sun– Hydrogen bomb
• never used in wartime• 10X power of atomic bomb• Initial heat produced by a small
atomic bomb inside• Hydrogen Bomb Video
Innovations in Nuclear Chemistry
• Particle accelerators – “atom smashers”
• Large Hadron Colider – CERN– Opened Sept. 09, 2008