The shape of the lesson
By the end of the lesson, learners can
- Aim at the nucleus: Fire alpha particles past a nucleus and vary the aim.
- Three kinds of radiation: Each differs in composition, charge and penetration.
- Conservation in decay: Two quantities must balance on both sides of every nuclear equation.
- Notation: A nucleons, Z protons.
- Conserved: A and Z balance.
- Alpha: A−4, Z−2.
One picture every idea returns to
Alpha-particle scattering showed the atom has a tiny, dense, positively charged nucleus surrounded by mostly empty space. A nuclide is written as nucleon number A over proton number Z. Isotopes share the same Z but differ in A. In every nuclear change, nucleon number and charge are conserved. Alpha radiation is a helium nucleus (charge +2e), beta-minus is a fast electron (charge −e), and gamma is a high-energy photon (no charge or mass).
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, A tiny, dense nucleus.. Fire alpha particles at a thin gold foil and almost all sail through, but a rare few bounce straight back. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Aim at the nucleus | Fire alpha particles past a nucleus and vary the aim. Project tab 1 of the lab (The nuclear atom) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Three kinds of radiation | Each differs in composition, charge and penetration. | Pairs |
| 21 to 30 min | Teach and check: Conservation in decay | Two quantities must balance on both sides of every nuclear equation. | Cooperative Concept Mapping |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 14 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Conservation in decay, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Cooperative Concept Mapping
Teams receive the key terms on cards and arrange them on a large sheet, drawing and labelling the links. Compare maps between teams before showing the model map.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Most alpha particles pass straight through the foil because the atom is mostly empty space; only a near head-on approach to the tiny nucleus gives a large deflection. | In a decay equation, balance both the nucleon number A and the charge Z. In beta-minus decay the nucleon number stays the same (a neutron turns into a proton), so only Z changes, rising by one. |
The atom and radiation: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
State the main conclusion drawn from the alpha-particle scattering experiment.
For the nuclide carbon-14 (A = 14, Z = 6), state the number of protons and neutrons.
Radium-226 (Z = 88) decays by alpha emission. Write the nucleon and proton numbers of the daughter nucleus and of the alpha particle, and show that they balance.
Carbon-14 (Z = 6) decays by beta-minus emission to nitrogen. State the nucleon and proton numbers of the daughter nucleus and explain the change in Z.
Compare the penetrating power of alpha and gamma radiation.
Define the term isotope.
Answer key and marking notes
- Almost all the mass and all the positive charge of an atom are concentrated in a tiny nucleus ✓
- and the atom is mostly empty space ✓
- Protons = Z = 6 ✓
- Neutrons = A − Z = 14 − 6 = 8 ✓
- Daughter: A = 226 − 4 = 222, Z = 88 − 2 = 86 (radon) ✓
- Alpha particle: A = 4, Z = 2 ✓
- Check: 222 + 4 = 226 and 86 + 2 = 88, so both balance ✓
- Daughter: A = 14 (unchanged), Z = 6 + 1 = 7 (nitrogen) ✓
- A neutron changes into a proton, so the proton number rises by one while the nucleon number stays the same ✓
- Alpha is the least penetrating, stopped by paper or a few centimetres of air ✓
- Gamma is the most penetrating, needing thick lead or concrete to reduce it significantly ✓
- Isotopes are atoms of the same element (same proton number) ✓
- but with different numbers of neutrons, and hence different nucleon numbers ✓
14 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Alpha-particle scattering showed that the atom has a:
- Atiny, dense, positive nucleus
- Blarge negative core
- Cuniform positive charge
- Dsolid structure
The nucleon number A of a nuclide is the number of:
- Aprotons only
- Bneutrons only
- Cprotons plus neutrons
- Delectrons
The proton number Z of a nuclide is the number of:
- Aneutrons
- Bprotons
- Cnucleons
- Delectrons plus protons
Isotopes of an element differ in their number of:
- Aprotons
- Belectrons in the neutral atom
- Cnucleons equal to Z
- Dneutrons
An alpha particle is:
- Aa helium nucleus (2 protons, 2 neutrons)
- Ban electron
- Ca photon
- Da proton
A beta-minus particle is:
- Aa helium nucleus
- Ba photon
- Ca fast-moving electron
- Da positron
Gamma radiation is:
- Aa helium nucleus
- Ba high-energy photon with no charge
- Can electron
- Da neutron
In alpha decay, the nucleon number and proton number change by:
- A−2 and −4
- B0 and +1
- C−1 and 0
- D−4 and −2
In beta-minus decay, the proton number Z:
- Aincreases by 1
- Bdecreases by 1
- Cincreases by 2
- Dstays the same
Most alpha particles pass straight through a thin gold foil because:
- Athe nucleus is negative
- Balphas are uncharged
- Cthe atom is mostly empty space
- Dthe foil is very thick
Carbon-14 has A = 14 and Z = 6. Its number of neutrons is:
- A6
- B8
- C14
- D20
In every nuclear decay equation, the quantities that must balance are:
- Amass and speed
- Benergy and momentum only
- Cthe number of electrons
- Dnucleon number and charge
The charge on an alpha particle is:
- A+2e
- B−e
- C0
- D+e
Of alpha, beta and gamma, the most penetrating is:
- Aalpha
- Bbeta
- Cgamma
- Dthey are equal
Quiz key
Most alphas pass through; a few deflect sharply, revealing a small dense positive nucleus.
A = protons + neutrons.
Z = number of protons.
Isotopes share Z but differ in neutron number.
Alpha = 2 protons + 2 neutrons.
Beta-minus is an electron emitted from the nucleus.
Gamma is an uncharged, massless electromagnetic photon.
Alpha decay reduces A by 4 and Z by 2.
A neutron becomes a proton, so Z rises by 1.
The nucleus is tiny, so most alphas miss it and continue almost undeflected.
Neutrons = A − Z = 14 − 6 = 8.
A and Z (charge) are conserved.
Two protons give a charge of +2e.
Gamma is the most penetrating, needing thick lead or concrete.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.