Chemistry • Year 11 • Module 1 • Lesson 20
Nuclear Chemistry
Secure the core vocabulary for radiation types, nuclear equation notation, and half-life before moving to applied questions.
1. Term–definition match
The definitions below are shuffled. In the right-hand column write the matching term from this list: radioisotope, alpha particle, beta particle, gamma ray, transmutation, half-life, mass number, atomic number. 8 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | An isotope with an unstable nucleus that spontaneously decays, releasing radiation. | |
| 1.2 | A helium nucleus (2 protons + 2 neutrons) emitted during a certain type of nuclear decay. | |
| 1.3 | A high-speed electron emitted when a neutron inside the nucleus converts to a proton. | |
| 1.4 | A high-energy electromagnetic photon released as a nucleus loses excess energy, with no mass or charge. | |
| 1.5 | The change of one element into another as a result of a nuclear reaction. | |
| 1.6 | The time taken for half of the radioactive nuclei in a sample to decay. | |
| 1.7 | The total number of protons plus neutrons in a nucleus, written as the top number in nuclide notation. | |
| 1.8 | The number of protons in a nucleus, written as the bottom number in nuclide notation. |
2. True or false, with correction
Circle T or F for each statement. If the statement is false, write the corrected version on the line below it. 10 marks (1 T/F + 1 correction each)
2.1 Gamma radiation has the highest penetrating power of the three types of ionising radiation. T / F
2.2 An alpha particle has a charge of +2 and is stopped easily by a sheet of paper. T / F
2.3 In beta decay, the mass number of the nucleus decreases by 4 and the atomic number decreases by 2. T / F
2.4 Half-life is the fixed amount of time it takes for an entire radioactive sample to completely disappear. T / F
2.5 Carbon-14 is a natural radioisotope formed in the upper atmosphere and used for radiocarbon dating. T / F
3. Fill-in-the-blank paragraph
Use the word bank to complete the passage. Each word is used once. 7 marks (1 per blank)
Word bank:
alpha · beta · gamma · mass number · atomic number · probability · half-life
A balanced nuclear equation must conserve both the total ___________ (top number) and the total ___________ (bottom number) across both sides. In ___________ decay, a helium nucleus is emitted, and both the mass number and atomic number decrease. In ___________ decay, a fast electron is emitted, the mass number stays the same but the atomic number increases by 1. ___________ radiation is a photon with no mass or charge. The ___________ of a radioisotope is the time for half of its nuclei to decay, this is a statement of ___________, not a fixed countdown for any single atom.
4. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 Why does alpha radiation have a much lower penetrating power than gamma radiation?
4.2 What two numbers must be conserved in a balanced nuclear equation?
4.3 Give one natural radioisotope and one human-made radioisotope, and state one use for each.
4.4 Why is technetium-99m's short half-life (about 6 hours) an advantage for medical imaging?
5. Complete the radiation properties table
For each type of radiation, write its notation, charge and relative mass. The first row is completed as an example. 9 marks (1 per blank cell)
| Radiation | Notation | Charge | Relative mass |
|---|---|---|---|
| Alpha | ⁴₂He | +2 | 4 |
| Beta | |||
| Gamma |
Q1, Term–definition match
1.1 radioisotope • 1.2 alpha particle • 1.3 beta particle • 1.4 gamma ray • 1.5 transmutation • 1.6 half-life • 1.7 mass number • 1.8 atomic number.
Q2, True / false with correction
2.1 True.
2.2 True.
2.3 False. Beta decay leaves the mass number unchanged and increases the atomic number by 1 (a neutron converts to a proton). It is alpha decay that decreases the mass number by 4 and the atomic number by 2.
2.4 False. Half-life is the time for half of the nuclei in a sample to decay, not for the whole sample to disappear. Each half-life only halves whatever amount remains, the sample never mathematically reaches exactly zero.
2.5 True.
Q3, Cloze paragraph
In order: mass number / atomic number / alpha / beta / Gamma / half-life / probability.
Q4.1, Alpha vs gamma penetrating power
Alpha particles are large (a full helium nucleus) and heavily charged (+2), so they interact strongly with matter and lose their energy over a very short distance, stopped by paper or skin. Gamma rays have no mass or charge, so they interact weakly with matter and can travel much further before losing their energy, requiring thick lead or concrete to stop them.
Q4.2, Conserved quantities
Total mass number (A) and total atomic number (Z) must both be conserved (equal on both sides) in every balanced nuclear equation.
Q4.3, Natural and human-made radioisotopes
Natural: carbon-14 (C-14), used for radiocarbon dating of once-living material. Human-made: technetium-99m (Tc-99m), used as a medical imaging tracer (or cobalt-60, used in cancer radiotherapy).
Q4.4, Why Tc-99m's short half-life helps
A short half-life means the radioisotope decays away quickly after the scan is complete, minimising the total radiation dose absorbed by the patient, while still being active long enough to complete the diagnostic imaging procedure.
Q5, Radiation properties table
Beta: notation ⁰₋₁e | charge −1 | relative mass ≈0 (1/1836). Gamma: notation γ | charge 0 | relative mass 0.