Year 8 Science · Unit 2 · Lesson 04
Challenge Worksheet
Learning Goals
Find the errors
This paragraph has exactly four errors. Underline each one and correct it below.
A student’s history of the atom
In about 1803, Dalton proposed that every atom has a tiny nucleus. Thomson later discovered the neutron. In 1911, Rutherford’s gold-foil results showed that the atom is a solid ball with no empty space. Because these older models were replaced, they were useless, and the scientists should have known better.
1. Write the four corrections.
Put the neutron story in order
These four stages show how the nuclear model was revised. Number them 1 to 4.
| Stage (1–4) | What happened |
|---|---|
| In 1932, Chadwick’s experiments detect a neutral particle with about the same mass as a proton. | |
| The model is updated: protons and neutrons in the nucleus, electrons outside. | |
| Scientists notice that most atoms have more mass than their protons alone can account for. | |
| Scientists suggest the nucleus also holds a particle with mass but no charge. |
| Model | Atoms rearrange in chemical reactions | Atoms contain electrons | A few alpha particles bounce back from gold foil | Electrons have separate energy levels |
|---|---|---|---|---|
| Dalton: solid sphere | ✓ | ✗ | ✗ | ✗ |
| Thomson: plum pudding | ✓ | ✓ | ✗ | ✗ |
| Rutherford: nuclear | ✓ | ✓ | ✓ | ✗ |
| Bohr: shells | ✓ | ✓ | ✓ | ✓ |
Source: summary of the models in this lesson.
2. Was Thomson’s model a failure? Use Table 1 to name the evidence it could explain and the evidence that forced it to be replaced, then give your judgement.
Model something you cannot see
The hidden-shape board
Your teacher tapes a cardboard shape under a large tray so you cannot see it. You roll marbles under the tray from different starting points and watch where each one comes out. Like Rutherford, you must build a model of something you cannot see.
3. Describe how you would use the marbles to build a model of the hidden shape: what you would change, what you would record, and how you would turn the results into a sketch. Then give one way the model could still be wrong, and one way to test it.
Someone claims
“The Bohr model should no longer be taught in schools, because scientists now know electrons do not move in neat circles. Students should only learn the quantum model. Teaching an incorrect model gives students the wrong idea about atoms.”
4. Evaluate the claim. Say which part is correct, what is misleading about it, and what should decide which atomic model is taught in Year 8.
Find the errors
1. (i) Dalton’s atom was a solid, indivisible sphere with no nucleus. (ii) Thomson discovered the electron (1897), not the neutron. (iii) Rutherford showed the atom has a tiny, dense nucleus and is mostly empty space. (iv) Replaced models were not useless: each was the best explanation of the evidence at the time, and later models built on them. [4 marks: 1 per correction]
Put the neutron story in order
Reading down the table as printed: 3, 4, 1, 2.
Your Turn
2. Could explain: atoms rearranging in reactions, and atoms containing electrons (it was the first model to include electrons, which every later model kept). Forced out by: a few alpha particles bouncing back from gold foil. Judgement: not a failure; it was the best model for the evidence of its time and a step towards the nuclear model. [4 marks: 1 evidence explained, 1 evidence not explained, 2 reasoned judgement]
Model something you cannot see
3. Change the starting point of the marble (evenly spaced points along each side), keeping the same marble and push; record where each marble comes out, repeating each point. Model: where marbles pass straight through there is no shape; where they turn or bounce back, the shape’s edge is there, so join those points to sketch the outline. Could be wrong: small details (narrow gaps, sharp corners) between the paths are missed. Test: roll more marbles at closer spacing, or from another side, and check that they come out where the model predicts. [4 marks: 1 variable changed and result recorded, 1 how results become a model, 1 limitation, 1 test]
Show What You Know
4. Marking guide: 1 correct part: electrons do not move in neat circles, so the Bohr model is not an exact picture; 2 what it gets right: a central nucleus with electrons outside, and electrons in separate energy levels, which is enough to explain bonding and the periodic table; 1 misleading: every model is wrong somewhere, so “incorrect” is not a reason to drop a model that is useful; 1 comparison: the quantum model is more accurate but mathematically complex, so it adds little for a Year 8 purpose; 1 judgement: keep teaching the Bohr model, and teach its limits too. [6 marks]
Common error to watch for: in the error hunt, changing Thomson’s discovery to the proton. Thomson discovered the electron; Chadwick discovered the neutron in 1932.