Atomic Structure

• Atom


  The smallest unit of an element that still retains its properties
• The word 'atom' means 'uncuttable' and was thought to be the smallest thing, but it is not the smallest thing we know
• Atom structure


  • Protons and neutrons in the nucleus
  • Electrons in outer shells
• Proton


  Mass of 1, charge of +1
• Neutron


  Mass of 1, no overall charge
• Electron

  Mass is 1/1800 of proton/neutron, charge of -1
• Mass number


  Number of protons plus number of neutrons
• Atomic number


  Number of protons, also equal to number of electrons
• Boron

  • Mass number 11, atomic number 5
• Number of neutrons = mass number - atomic number
• Atoms have the same number of positive and negative charges, so no overall charge
• Isotopes

  • Atoms with the same atomic number but different mass numbers
• Models of the atom

  • Ancient Greek 'uncuttable'
  • J.J. Thomson 'plum pudding'
  • Rutherford 'positive centre'
  • Bohr 'nuclear model'
• 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 positive centre with negative charges around
• Types of radiation

  • Alpha (helium nuclei)
  • Beta (electrons)
  • Gamma (electromagnetic waves)
• Alpha radiation


  • Highly ionizing, not very penetrating
• Beta radiation


  • Moderately ionizing, more penetrating than alpha
• Gamma radiation


  • Not ionizing, highly penetrating
• Radiation detection

  Geiger-Muller tube, clicks for each radiation detection
• Radiation unit

  Becquerel (Bq)
• Half-life


  Time for half the radioactive atoms to decay
• Alpha decay

  Uranium-238 to thorium-234
• Beta decay


  Uranium-238 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)
• Uses of radioactivity

  • Gamma - cancer treatment, sterilization
  • Beta - thickness testing
  • Alpha - smoke alarms
• Nuclear fission

  1. Splitting of heavy nuclei, releasing neutrons and radiation

  2. Chain reaction as released neutrons hit other nuclei
• Nuclear fusion


  Combining light nuclei to form heavier nuclei, releasing energy