Year 8 Science · Unit 2 · Lesson 11
Challenge Worksheet
Learning Goals
Find the errors
This comparison contains exactly four errors. Underline each one and correct it below.
A student’s model comparison
Dalton’s model is useful for showing that atoms contain electrons. Thomson’s model shows that atoms contain electrons, but it has no nucleus. Rutherford’s model shows a tiny, dense nucleus and explains exactly how the electrons are arranged in shells. Bohr’s model shows electrons in energy levels, but it cannot explain the colours of light given off by complex atoms. The quantum model is the most accurate, so it is the best model for every question. In the end, a diagram is useful if it is detailed and colourful.
1. Write the four corrections.
Score the models
Scenario: a scoring table
A student scored five atomic models (0 = no, 1 = partly, 2 = yes) and concluded: “Bohr and quantum have the same total, so they are equally useful. Dalton has the lowest total, so it is the least useful model for any question.”
| Model | Simple to draw | Shows electrons | Shows a nucleus | Shows energy levels | Explains neon sign colours | Total |
|---|---|---|---|---|---|---|
| Dalton | 2 | 0 | 0 | 0 | 0 | |
| Thomson | 2 | 2 | 0 | 0 | 0 | |
| Rutherford | 2 | 2 | 2 | 0 | 0 | |
| Bohr | 2 | 2 | 2 | 2 | 0 | |
| Quantum | 0 | 2 | 2 | 2 | 2 |
Source: sample scores from one student.
2. Complete the Total column. Then a teacher asks which model best explains to Year 8 why elements in one column of the periodic table react alike. She says only three criteria matter (simple to draw, shows a nucleus, shows energy levels) and that “simple to draw” counts double. Calculate the new totals for Rutherford, Bohr and quantum.
Rutherford Bohr Quantum
Evaluate the conclusion
3. Use your results to evaluate both parts of the student’s conclusion.
4. Evaluate: “All atom diagrams are interchangeable; it does not matter which one you draw.” Give two examples of a question where one diagram works and another does not.
Find the errors
1. (i) Dalton’s model is a solid, indivisible sphere with no electrons (Thomson first included them). (ii) Rutherford’s model does not explain how electrons are arranged; electron shells come from the Bohr model. (iii) The quantum model is the most accurate but mathematically complex; the best model is the simplest one that answers the question. (iv) A diagram is useful if it clearly shows what the question needs, not because it is detailed or colourful. [4 marks: 1 per correction]
Score the models
2. Totals: Dalton 2, Thomson 4, Rutherford 6, Bohr 8, quantum 8. New totals: Rutherford 4 + 2 + 0 = 6; Bohr 4 + 2 + 2 = 8; quantum 0 + 2 + 2 = 4. [4 marks: 1 Total column, 1 each new total]
3. “Equally useful” is weak: they tie only because every criterion counts the same; with criteria that match the Year 8 purpose, Bohr scores 8 and quantum 4, while for neon colours only quantum scores. “Dalton is least useful for any question” is weak: to show atoms rearranging in reactions, Dalton’s simple model is enough. Usefulness depends on the question, so one total cannot rank models for every purpose. [4 marks: 2 per part, each using data or an example]
Show What You Know
4. Marking guide (points expected): 1 each diagram shows some features and leaves others out (Dalton: no parts; Bohr: nucleus and shells, not exact electron behaviour); 2 two examples, such as: Dalton cannot explain why sodium and potassium react alike, Bohr can (one outer electron each); Thomson cannot explain alpha particles bouncing back from gold foil, Rutherford can; Bohr cannot explain the exact colours of a neon sign, the quantum model can; 1 so the diagrams are not interchangeable; 1 some overlap (Rutherford and Bohr both show a nucleus); 1 judgement: choose the simplest diagram that shows what the question needs. [6 marks]
Common error to watch for: in Q2, doubling every score instead of only “simple to draw”.