Year 8 Science · Unit 2 · Lesson 06
Challenge Worksheet
Learning Goals
Find the errors
This paragraph contains exactly three errors. Underline each one and write the correction below.
A student’s summary
Protons carry a positive charge and are found in the nucleus. Neutrons carry a negative charge and are also found in the nucleus. Electrons are found outside the nucleus, and because they are the heaviest of the three particles, they make up most of the atom’s mass. A neutral atom has the same number of electrons as protons, so the charges cancel out. The nucleus is small, but it still fills most of the space inside the atom.
1. Write the three corrections.
2. Beryllium’s nucleus holds 4 protons and 5 neutrons, and 4 electrons move around it. What is the total charge of the nucleus, and why does the whole atom have no overall charge?
Scenario: model atoms on the school oval
A science club wants to show how empty an atom is. They use the lesson’s rule: an atom is about 100 000 times wider than its nucleus. They plan three models.
| Model | Diameter of the nucleus | Diameter of the whole atom |
|---|---|---|
| Model A: a circle painted on the oval | 100 m | |
| Model B: a marble as the nucleus | 1 cm | |
| Model C: a football stadium | 200 m |
Source: sample club plan. The ratio of about 100 000 is rounded; the real ratio varies between atoms.
3. Calculate the diameter of the nucleus in Model A. Give your answer in metres and in millimetres.
Answer m, or mm
4. Calculate the diameter of the whole atom in Model B, in kilometres. Then find the nucleus size for Model C, and say whether the lesson’s comparison of the nucleus to “a fly on the centre circle” is reasonable.
Answer: Model B km; Model C mm
5. The club wants its models to be complete, so it plans to add the electrons. Explain why it would be almost impossible to show the electrons to the same scale in Model A, and suggest what the club should do instead so the model still teaches something true.
6. A student claims: “Every atom must contain neutrons, because without neutrons the protons would push each other apart.” Evaluate this claim. Say which part is supported by the lesson, which part is not, and give an example.
7. Evaluate the statement: “Atoms are just tiny solid balls.” Use your scale results from Table 1, and what you know about the nucleus, the electrons and where the atom’s mass is. Explain why the “solid ball” idea was still useful, and finish with a clear judgement.
Find the errors
1. (i) Neutrons carry no charge, not a negative charge. (ii) Electrons are the lightest particles; almost all of the mass is in the nucleus (protons and neutrons). (iii) The nucleus is tiny: the atom is about 100 000 times wider, so the atom is almost entirely empty space. [3 marks: 1 per correction]
Your Turn
2. +4 (four protons; neutrons have no charge). The 4 electrons give −4, which cancels the +4. [2 marks]
3. 100 m ÷ 100 000 = 0.001 m = 1 mm. [2 marks: 1 in m, 1 in mm]
4. Model B: 1 cm × 100 000 = 100 000 cm = 1000 m = 1 km. Model C: 200 m ÷ 100 000 = 0.002 m = 2 mm. A fly is a few millimetres long, so the comparison is reasonable. [4 marks: 1 multiply, 1 convert to km, 1 Model C 2 mm, 1 judgement on the fly]
Go Deeper
5. The lesson pictures electrons as mere specks, far lighter than the nucleus, so at a scale where the nucleus is only 1 mm they could not be shown; they also move in the space around the nucleus rather than sitting at fixed points. Instead: use the painted circle to mark the region where electrons are found, labelled, or add markers with a sign saying they are not to scale. [3 marks: 1 too small at this scale, 1 electrons move in the space, 1 sensible labelled alternative]
6. Supported: with more than one proton, the positive protons repel, and neutrons help hold the nucleus together. Not supported: “every atom”: ordinary hydrogen has 1 proton and no neutrons, and one proton has nothing to push apart. Partly correct. [3 marks: 1 supported part, 1 hydrogen counter-example, 1 reason one proton needs no neutron]
Show What You Know
7. Marking guide (points expected): 1 scale evidence (a 1 mm nucleus in a 100 m atom), so an atom is almost entirely empty space; 1 nucleus: tiny, holds protons (+) and neutrons (no charge) and almost all the mass; 1 electrons (−) move in the space outside and set the size; 1 objects feel solid because electrons of two surfaces repel, not because atoms are solid; 1 useful: the ball idea works for simple particle diagrams and was useful historically; 1 judgement: wrong as a description of structure, acceptable as a simplified model for some jobs. [6 marks]
Common error to watch for: dividing when the question needs multiplying (Model B). Check the size of the answer: the whole atom must always be bigger than its nucleus.