Chemistry

• Isotopes


  Atoms of the same element that have the same number of protons but different number of neutrons
• Radioisotopes


  Unstable isotopes that emit radiation
• The atomic number = number of protons
• The atomic mass = number of protons + number of neutrons
• Mass Number


  The total number of protons and neutrons in the nucleus of an atom
• Isotopes of Cobalt


  • Cobalt-59
  • Cobalt-60
• Isotopes


  • Have the same number of protons but different number of neutrons
  • Always have the same atomic number but different atomic masses
• Isotopes of Hydrogen


  • Hydrogen 1
  • Hydrogen 2 (Deuterium)
  • Hydrogen 3 (Tritium)
• Most atoms that make the world around us are stable
• Some naturally occurring isotopes have unstable nuclei
• Elements with atomic numbers of 1-82 have isotopes (stable nucleus) and most have at least one radioisotope (unstable nucleus)
• Isotopes of elements with atomic numbers higher than 83 are all radioisotopes
• Stable Isotope


  Isotope with a stable nucleus
• Radioactive Isotope (Radioisotope)


  Isotope with an unstable nucleus that decays and emits radiation
• Radioactivity


  The release of energy from radioisotopes when they decay
• Atomic particles


  • Protons have a positive charge, electrons have a negative charge, and neutrons are neutral
  • ++ and - - charges repel each other and + - charges attract each other
• Strong Nuclear Force


  The force that holds the nucleus of an atom together and opposes the repulsion between protons
• Binding energy


  • The amount of energy released when forming a nucleus
  • The mass of the nucleus is always slightly less than the mass of the sum of protons and neutrons that make up the nucleus (mass defect)
  • This mass defect is transformed into energy
• Alpha Decay


  1. Removal of the equivalent of a helium atom (atomic number 2, atomic mass 4) to get to stable state

  2. Can be stopped by paper or 2cm of air
• Alpha Decay


  • Decay of Radon (atomic number 86, atomic mass 222)
  • Decay of Polonium (atomic number 84, atomic mass 218)
• Negative Beta Decay


  1. A neutron becomes a proton and a beta particle (an electron) is emitted together with an antineutrino

  2. Can be stopped by a hand, aluminium or wood
• Positive Beta Decay


  1. A proton becomes a neutron and a beta particle (a positron) is emitted together with a neutrino

  2. Can be stopped by a hand, aluminium or wood
• Gamma Radiation


  • The release of excess energy from a nucleus after it undergoes alpha or beta decay
  • Can be stopped by thick lead
• Half-life


  The time it takes for half of a radioactive sample to decay
• Formula to work out half-life


  1. (starting amount) x (1/2)^(number of half-lives) = remaining amount

  2. Number of half-lives = log (remaining amount/starting amount) / log (0.5)
• Working out the half-life


  • Example 1: Zinc-71 (half-life 2.4 minutes)

  Example 2: Osmium-182 (half-life 21.5 hours)

  Example 3: Francium-223 (half-life 25 years)

  Example 4: Uranium-242 (half-life 4 years)

  Example 5: Unknown sample (half-life 4 days)
• Nuclear Fusion


  The joining of small atomic nuclei, e.g. isotopes of hydrogen, to produce energy
• Nuclear Fission


  The splitting of large atomic nuclei, e.g. Uranium 235 and Plutonium 239, into smaller atomic nuclei to produce energy
• Neutrons


  Neutral particles in the nucleus of an atom
• Protons


  Positively charged particles in the nucleus of an atom
• Radioactive emissions


  1. Alpha (α)

  2. Beta (β)

  3. Gamma (γ)
• Alpha (α) radiation


  • Positively Charged
  • Stopped by thin paper or a few centimetres of air
• Beta radiation


  • Can have a positive or negative charge
  • Can travel through paper, but is stopped by aluminum
• Gamma (γ) radiation


  • Uncharged
  • Can travel through fairly thick lead
• Beta particle


  Electron emitted during beta decay
• Beta decay


  Neutron → Proton + Electron + Antineutrino
• Alpha decay


  Unstable nucleus → Stable nucleus + Alpha particle
• To find the number of protons, look at the atomic number
• To find the number of neutrons, subtract the atomic number from the mass number
• If an atom has 35 protons, it will have 35 electrons orbiting the nucleus