Year 8 Science · Unit 2 · Lesson 10

Comparing Atomic Models

Challenge Worksheet

Name

Date

Class

Learning Goals

Evaluate how experimental evidence shapes the atomic model proposed
Rank and justify the usefulness of models for a specific scientific purpose
Construct extended arguments using scientific reasoning about models and evidence

Go Deeper

What if…?

Scenario

In 1909, Hans Geiger and Ernest Marsden conducted the famous gold-foil experiment under Rutherford's direction at the University of Manchester. They fired positively charged alpha particles at an ultra-thin sheet of gold. What they actually observed: most particles passed straight through, a small number deflected slightly, and, most importantly, a tiny fraction bounced almost directly back.

What if the result had been completely different? Imagine that instead of what really happened, every single alpha particle deflected by a small amount, say 5° to 15°, with none passing straight through and none bouncing straight back. Every particle was deflected slightly, equally, in all directions.

Using what you know about how experimental evidence shapes atomic models, predict what atomic structure Rutherford would have proposed based on this alternative result. Explain how this would have changed our understanding of atomic structure, including what scientists would have concluded about empty space inside the atom, and whether a central nucleus would have been proposed. Use scientific terms in your answer.

Challenge 4 marks

Show What You Know

1. Rank the four models, Dalton, Thomson, Rutherford, Bohr, from least useful to most useful for a Year 8 student doing Stage 4 chemistry (e.g. drawing electron configurations, explaining why elements in the same group behave similarly, predicting reactivity). Write your ranking from 1 (least useful) to 4 (most useful), then justify each position in one or two sentences by stating what that model explains, or fails to explain, for these chemistry tasks.

Challenge 4 marks

2. A student argues: "The Bohr model must be wrong because it doesn't describe electrons the way quantum mechanics does, so we should not teach it." Evaluate this argument. In your response, explain what it means for a model to be useful rather than true, and give one specific example from this lesson to support your evaluation.

Challenge 3 marks

Wrap Up

In one sentence, what was the main idea of this lesson?