Atomic structure

• Atom


  The smallest unit of an element that still retains its properties
• The Greeks who named the atom thought it was the smallest thing, but it isn't the smallest thing we know
• Atom size


  Not 0.1 to 0.5 nanometers, which is 1 x 10^-10 to 5 x 10^-10 meters
• Parts of an atom

  • Protons
  • Neutrons
  • Electrons
• Nucleus


  The central part of an atom, where protons and neutrons are located
• Proton


  Has a mass of 1 and a charge of +1
• Neutron


  Has a mass of 1 and no overall charge
• Electron


  Has a mass of 1/1836 that of a proton or neutron, and a charge of -1
• Mass number


  The total number of protons and neutrons in an atom
• Atomic number


  The number of protons in an atom, which is also equal to the number of electrons
• Boron


  • Mass number 11, atomic number 5, 6 neutrons
• An atom has the same number of positive and negative charges, so it has no overall charge
• Isotopes of carbon


  • Both have 6 protons and 6 electrons, but different numbers of neutrons (6 vs 8)
• Atom model development


  • Ancient Greece - 'atom' meaning uncuttable
  • J.J. Thomson - plum pudding model
  • Rutherford - positive centre with negative charges around
  • Bohr - nuclear model with electrons orbiting
• Rutherford's gold foil experiment

  1. Fired particles at gold foil

  2. Majority went straight through

  3. Some deflected a little

  4. Some deflected a lot

  5. Showed atom has a positive centre with empty space
• Types of radiation


  • Alpha
  • Beta
  • Gamma
• Alpha radiation


  Helium nuclei, highly ionizing, not very penetrating
• Beta radiation


  Electrons, moderately ionizing, more penetrating than alpha
• Gamma radiation


  Electromagnetic waves, not ionizing, highly penetrating
• Alpha radiation can be stopped by paper or skin, beta by aluminium foil, gamma by thick lead
• Geiger-Muller tube


  Measures radiation, clicks for each particle detected
• Becquerel


  Unit of radiation
• Half-life


  Time for half the radioactive atoms to decay
• Uranium-238 decay


  • Alpha decay to thorium-234
  • Beta decay to neptunium-234
• Sources of background radiation

  • Radon gas (50%)
  • Medical (14%)
  • Ground (14%)
  • Food/drink (11.5%)
  • Cosmic (10%)
  • Nuclear weapons testing (0.2%)
  • Air travel (varies)
  • Nuclear power (tiny)
• Gamma radiation


  Used for cancer treatment and sterilizing materials due to high penetration
• Beta radiation


  Used for testing thickness of materials due to short range
• Alpha radiation


  Used in smoke alarms due to long half-life
• Nuclear fission


  1. Neutron hits heavy radioactive element

  2. Splits nucleus

  3. Releases more neutrons

  4. Chain reaction
• Nuclear fusion


  Light nuclei combine to form heavier nuclei, releasing energy