Atomic Structure

• Rutherford replaced the plum pudding model with the nuclear model
• What is the order of atom discovery

  Dalton, JJ Thompson, Rutherford, Bohr
• What did the plum pudding model suggest

  Atoms were spheres of positive charge with tiny negative electrons stuck in them.
• What was Rutherford's experiment

  Alpha Scattering Experiment - Firing a beam of alpha particles at thin gold foil
• Isotopes of an Element

  Atoms with the same number of protons but a different number of neutrons.
• Alpha Particles

  • They are helium nuclei
  • 2 neutrons and 2 protons
  • Weak penetrating
  • Highly ionising
• Beta Particles

  • An electron
  • Charge of -1
  • Moderatly penetrating and ionising
  • For every beta particle emitted, a neutron in the nucleus has turned into a proton.
• Gamma Rays

  • Waves of electromagnetic radiation
  • High penetrating
  • Weak ionising
• Alpha Decay decreaes the charge and mass of the nucleus
• Beta Decay increases the charge of the nucleus
• Gamma rays dont change the charge or mass of the nucleus
• Radioactivity is a totally random process
• Radiation can be measured with a geiger miller tube and counter.
• The radioactivity of a source decreases over time
• The half-life is the time taken for the number of radioactive nuclei in an isotope to halve
• Examples of background radiation are nuclear explosions, food, space
• Exposure to Radiation is called irradiation
• Contamination is radioactive particles getting onto objects
• The severity of irradiation and contamination depends on the source
• Risks of radiation

  • Tissue damage
  • Kills cells - can lead to cancer
  • Higher doses can kill cells completley
• Gamma sources can be used in medical tracers because they have

  • Low ionisation and short half lives
• High doses of radiation can be used ti kill lots of living cells which can be used to treat cancer
• Nuclear Fission - Splitting a large, unstable nucleus
• Nuclear Fission

  • Is spontaneous
  • Used to release energy by splitting unstable atoms into smaller atoms.
  • 2-3 neutrons are released when the atom splits
  • If neutron is moving slow enough to be absorbed by other nucleas then fission can occur again
• Nuclear Fusion - Joining small nuclei
• In fusion

  • Two light nuclei collide at high speed and fuse to create larger, heavier nucleus.
  • The heavier nucleus produced does not have as much mass as the two seperate nuclei did because some of the mass is converted into energy.