P4

• What is the topic of AQA P4?

  Atomic Structure and Nuclear Radiation
• Are there any required practicals in this topic?

  No required practicals
• What are the key models of the atom's development?

  • Simple atom: tiny solid spheres
  • Plum pudding model: positive charge with embedded electrons
  • Nuclear model: nucleus with protons and neutrons
  • Electrons in shells: fixed orbits proposed by Niels Bohr
• What did the simple atom model believe about atoms?

  They were tiny solid spheres
• What was the plum pudding model?

  A ball of positive charge with electrons embedded
• What was discovered about the electron?

  It is smaller than an atom
• What characterizes the nuclear model of the atom?

  Positively charged nucleus surrounded by electrons
• Who discovered the nuclear model?

  Rutherford
• What experiment led to the discovery of the nucleus?

  Rutherford's alpha particle scattering experiment
• What do electrons do in the nuclear model with shells?

  Orbit the nucleus at specific distances
• Who proposed that electrons orbit in fixed shells?

  Niels Bohr
• What did Chadwick discover about the nucleus?

  It contains neutrons as well as protons
• What are the types of nuclear radiation and their properties?

  • Alpha (α): 2 protons and 2 neutrons, blocked by skin/paper, range ~5cm, highly ionising
  • Beta (β): high-speed electron, blocked by thin aluminium, range ~1m, medium ionising
  • Gamma (γ): electromagnetic wave, blocked by thick lead, infinite range, weakly ionising
• What is the radius of an atom?

  $1 \times 10^{-10} \text{ metres}$
• What is the charge of the nucleus?

  Positive charge
• What happens when an electron absorbs electromagnetic radiation?

  It moves further from the nucleus
• What is the atomic number?

  Number of protons (and electrons)
• What does atomic mass indicate?

  Number of protons plus neutrons
• What is an isotope?

  Same number of protons, different neutrons
• What is nuclear radiation?

  A random process from unstable nuclei
• What is nuclear decay?

  When radiation is released
• What is activity measured in?

  Bequerels (Bq)
• What is count rate?

  Number of decays per second measured
• What is half-life?

  Time for half of unstable nuclei to stabilize
• What is irradiation?

  Exposure to radiation without becoming radioactive
• What is contamination?

  Radioactive particles get on or into an object
• What precautions can be taken to reduce radiation exposure?

  • Reduce exposure time
  • Increase distance from source
  • Wear protective equipment
• What is the net decline ratio after 1 half-life?

  1/2
• What is the net decline ratio after 2 half-lives?

  1/4
• What is the net decline ratio after 3 half-lives?

  1/8
• What are the uses of radioactive isotopes?

  • Alpha: smoke alarms, easily blocked, highly ionising
  • Beta: check paper thickness, partially blocked by paper
  • Gamma: medical tracers, weakly ionising, passes through materials
• What is the difference between short and long half-lives?

  • Short half-life: highly radioactive initially, decays quickly
  • Long half-life: less radioactive, remains radioactive longer