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


  0.1 to 0.5 nanometers (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
• The number of protons equals the atomic number, the number of neutrons equals the mass number minus the atomic number
• 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' means uncuttable
  • J.J. Thomson - plum pudding model
  • Rutherford - positive center with negative charges
  • Bohr - nuclear model with electrons orbiting
• Rutherford's gold foil experiment

  Most particles went straight through, some were deflected a little, and a few were deflected a lot, indicating a positive center 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
• Geiger-Muller tube


  Measures radiation, clicks for each particle detected
• Becquerel (Bq)


  Unit of radioactivity, measures the number of radioactive decays per second
• Half-life


  The time it takes for half of the radioactive atoms to decay
• Radioactive decay calculations


  Use atomic number to determine new element after alpha or beta decay
• Sources of background radiation

  • Radon gas
  • Medical procedures
  • Ground/soil
  • Food and drink
  • Cosmic radiation
  • Nuclear weapons testing
  • Air travel
  • Nuclear power
• Uses of radioactivity


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


  Splitting of heavy nuclei, releases neutrons that can split other nuclei in a chain reaction
• Nuclear fusion


  Combining of light nuclei to form heavier nuclei, releases energy
• Radiotherapy


  Used to treat cancer
• Medical tracers

  Can help detect problems inside the body
• Ionizing radiation can damage cells

  By ionizing the atoms and molecules within them
• Large doses of radiation across the body

  Can lead to radiation sickness with symptoms like vomiting, tiredness and hair loss
• Radiotherapy


  Uses radiation to destroy cancer cells
• External radiotherapy


  1. Emits gamma rays targeted at the cancer site from multiple angles

  2. Only the cancer site gets the highest dose
• Internal radiotherapy

  1. Places a radioactive source inside the body, either in the cancer itself or next to it

  2. Usually uses more damaging beta radiation
• Both external and internal radiotherapy have side effects as healthy cells also get damaged or killed
• Medical tracers


  Radioactive isotopes injected or swallowed to track their movement around the body and check organ function
• Gamma rays are used for medical tracers as they are less harmful than alpha or beta radiation</b>
• Isotopes with short half-lives are used for medical tracers so they only emit radiation for a short period
• Radiation use in medicine involves weighing up the risks against the benefits