Year 8 Science · Unit 2 · Lesson 10

Comparing Atomic Models

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Learning Goals

Apply knowledge of atomic models to interpret a historical scientific scenario
Explain why a simplified model can still be more useful than a more accurate one
Identify which limitations of the Bohr model are irrelevant at Stage 4 level

Warm Up

Predict + reason

Scenario

A scientist working in 1905, six years after Thomson published his plum-pudding model but six years before Rutherford published his gold-foil results, is asked by a student: "What does the inside of an atom look like?" She answers honestly, using the best available model at the time. Rutherford's experiment is not yet known.

(a) Describe what the scientist's answer would look like. What would she say the atom contains, and how would she describe the arrangement of particles inside it?

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(b) Predict which specific part of her description would be proven wrong once Rutherford published his results in 1911. Explain why Rutherford's evidence overturned that part.

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Your Turn

Real-world scenario

Real-world context

Modern MRI (magnetic resonance imaging) machines used in Australian hospitals, including major centres such as Royal Prince Alfred Hospital in Sydney and the Royal Melbourne Hospital, rely on the quantum mechanical model of electron behaviour in atoms to function. The physics behind MRI depends on how electrons and nuclei behave according to quantum mechanics, not the simpler Bohr model. Yet every Year 8 student in Australia learns the Bohr model to understand how electrons are arranged in shells around the nucleus.

(a) Explain why the Bohr model, not the quantum mechanical model, is used in Year 8 science, even though the Bohr model is less accurate. Use the idea that a model's value depends on the question being asked.

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(b) Name one limitation of the Bohr model that does NOT matter when a Year 8 student is learning to draw electron configurations for simple elements like sodium or oxygen. Explain why that limitation can be ignored at this level.

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Show What You Know

1. A classmate says: "We should stop teaching the Bohr model because it isn't accurate." Do you agree or disagree? Use the idea of purpose to explain your position.

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2. For each question below, write which atomic model you would use and why.
(i) "Why do sodium and potassium react in similar ways?"
(ii) "Is the inside of an atom mostly empty space?"

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Wrap Up

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