Year 9 Science Exam Prep — Episode 9: Atomic Structure and Radioactivity

Episode Overview

• Subatomic particles: protons, neutrons, and electrons (charges, masses, locations)
• Atomic number and mass number — how to calculate the number of neutrons
• Isotopes — what they are, why they have the same chemical properties, and the carbon-14 dating example
• The development of the nuclear model: Dalton → Thomson's plum pudding model → Rutherford's gold foil experiment → Bohr's electron shells → Chadwick's neutron
• The gold foil experiment: what was expected, what was observed, and what it proved
• The three types of radioactive decay: alpha, beta, and gamma — properties, penetration, ionising power, and dangers
• Writing and balancing nuclear equations for alpha and beta decay
• Half-life: what it means, worked calculation examples, and how to work backwards
• Uses of radioactivity: medical tracers, radiotherapy, carbon dating, smoke detectors, nuclear power
• Dangers of radiation and safety measures

Exam Tips Covered

1. Always check mass numbers and atomic numbers balance on both sides of a nuclear equation.
2. For half-life calculations, count half-lives first — never divide the amount directly by time.
3. For the gold foil experiment, describe what was observed and then explain what it tells us.
4. Always state whether a radiation hazard question is about internal or external exposure.
5. Learn key half-lives: Carbon-14 (~5,730 years), Americium-241 (~432 years), Iodine-131 (~8 days).

Revision Suggestion

• The subatomic particles table (particle, location, charge, mass)
• The alpha / beta / gamma comparison table
• One worked half-life calculation