GCSE Physics: Atomic Structure & Radioactivity — Revision Workbook

Inside GCSE Physics: Atomic Structure & Radioactivity — Revision Workbook

label the atom and compare the size of the atom and the nucleus, order the atomic model from plum pudding to Rutherford and Bohr, sort the types of nuclear radiation by penetration and ionising power, work out the mass and atomic number changes in alpha and beta decay, then calculate half-lives and tell contamination from irradiation. About 30 minutes.

Learning objectives

• the structure of the atom — a central nucleus of protons and neutrons with electrons in shells, and the huge difference in size between the atom (about 1×10⁻¹⁰ m) and its nucleus (about 1×10⁻¹⁴ m);
• the development of the atomic model — from the plum-pudding model to Rutherford’s nuclear model (from alpha-particle scattering) and Bohr’s energy levels;
• isotopes and the types of nuclear radiation — alpha (a helium nucleus), beta (a fast electron) and gamma, their penetration through paper, aluminium and lead, and their ionising power;
• radioactive decay, activity and nuclear equations — activity in becquerel, and the mass-number and atomic-number changes in alpha and beta decay;
• half-life, contamination and irradiation — calculating the activity left after a number of half-lives, finding a half-life from data, and the difference between contamination and irradiation, with the uses and dangers of radiation.

Activities in this book

1. Task 1 — Structure of the Atom & the Nuclear Model

   an atom has a tiny central nucleus of protons and neutrons, with electrons in shells (energy levels) around it. The atom is about 1×10⁻¹⁰ m across, but the nucleus is only about 1×10⁻¹⁴ m — around ten thousand times smaller. The model changed over time: plum pudding → Rutherford (nuclear model, from alpha scattering) → Bohr (electrons in fixed energy levels).

2. Task 2 — Isotopes & Types of Nuclear Radiation

   isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Unstable isotopes decay and give out radiation. An alpha particle is a helium nucleus (2 protons + 2 neutrons); a beta particle is a fast electron; gamma is a high-energy electromagnetic wave. Alpha is stopped by paper, beta by a few mm of aluminium, gamma only by thick lead — and alpha is the most strongly ionising, gamma the least.

3. Task 3 — Decay, Activity & Nuclear Equations

   the activity of a source is the number of nuclei that decay each second, measured in becquerel (Bq) with a Geiger-Muller tube. In alpha decay the nucleus loses 2 protons and 2 neutrons, so the mass number falls by 4 and the atomic number falls by 2. In beta decay a neutron turns into a proton and emits an electron, so the mass number is unchanged and the atomic number rises by 1.

4. Task 4 — Half-life, Contamination & Irradiation

   the half-life is the time it takes for the activity (or the number of undecayed nuclei) to halve. After each half-life the activity halves again: after n half-lives it is (½)ⁿ of the start. Contamination means getting radioactive atoms onto or into an object, so it keeps emitting radiation; irradiation means being exposed to radiation from an outside source, which does not make the object radioactive.

5. Task 5 — Explain Half-life & Radiation Safety (6 marks)

   this is an exam-style writing task, so it is not auto-marked. Aim for six clear points, using the correct keywords (activity, half-life, alpha, beta, gamma, ionising, contamination, irradiation).

Suggestions for teaching

• Label the atom first. Secure the nucleus, protons, neutrons and electrons in shells, then use the sizes to show the nucleus is about ten thousand times smaller than the atom.
• Order the models. Rehearse plum pudding → Rutherford (nuclear) → Bohr, and link the nuclear model to the alpha-particle scattering evidence.
• Sort the radiations. Drill alpha = helium nucleus, beta = fast electron, gamma = wave, and the paper / aluminium / lead penetration order alongside their ionising power.
• Balance the numbers. Model alpha decay (mass number −4, atomic number −2) and beta decay (mass number unchanged, atomic number +1) on a nuclear equation.
• Halve, then halve again. Build half-life confidence by repeatedly halving the activity, and by reading how many halvings fit a given time to find the half-life.