P4 - Atomic Structure

P4 - Atomic Structure

1. Structure of the Atom

   • Electron
     • Mass = close to 0 (1/2,000)
     • Charge = -1
   • Nucleus
     • Proton
       • Mass = 1
       • Charge = +1
     • Neutron
       • Mass = 1
       • Charge = 0

2. History of the Atom

   • Democritus
     • 400 BC - Atomos indivisible
   • John Dalton
     • 1803 - atom is the building block of all things, different types
   • JJ Thomson
     • 1898 - Plum pudding model (ball of +ve charge dotted with -ve charge)
   • Ernest Rutherford
     • 1909 - tiny nucleus all the mass and +ve charge
   • Niels Bohr
     • 1922 - electrons are in shells
   • James Chadwick
     • 1932 - discovered neutrons

3. Radioactivity

   • Types
     • Alpha
       • Charge = 2+
       • Mass = 4
       • Penetration = Only few cm in air, stopped by skin and paper
       • Ionisation = Very Ionising
     • Beta
       • Charge = 1-
       • Mass = 1/1832
       • Penetration = Few metres in air, stopped by aluminium foil
       • Ionisation = Fairly Ionising
     • Gamma
       • Charge = 0
       • Mass = 0
       • Penetration = Stopped by few metres of concrete, and thick lead
       • Ionisation = Weakly Ionising
   • Background Radiation
     • Measured using a Geiger-Muller Tube
     • Radiation that can be detected at all times
   • Tracers
     • A small amount of radiation used to detect things, eg pipe leaks
     • Medical tracers = use beta or gamma sources because they are less ionising than alpha cells, and wouldn't stay in your body causing damage

4. Decay equations

   • Alpha
     • -4 from the mass
     • -2 from the atomic number
   • Beta
     • -0 from the mass
     • -1 from the atomic number

5. Test Questions

   • Neutrons are the mass number-atomic number, e.g.
   • Use Beta to detect cracks in welds, etc, because Alpha won't penetrate at all, and Gamma will always penetrate.
   • Radioactive decay is described as random and spontaneous
   • Nuclear equation:
   • Hospital equipment becomes irradiated when it's exposed to radiation.
   • Irradiated equipment is not hazardous, because it does not have any radioactive isotopes.
   • Over time, contaminated hospital equipment is a medium hazard, and will become less of a hazard, due to it having fewer radioactive particles
   • The difference between nuclear fission and nuclear fusion, is that fission is when the nucleus splits into 2 smaller nuclei, and fusion is when 2 small nuclei join together to make one large nuclei.
   • The process of nuclear fission (using a specific equation)
   • When Uranium-235 and a neutron combine, it splits into 2 to get Ba and Kr. 3 neutrons get released, and they go on to carry on the chain reaction.

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