🎯 Success Criteria

By the end of this task, I can:

Explain how the atomic model changed with the discovery of subatomic particles

Define half-life and radioactive decay

Calculate half-life from given data

Interpret decay graphs and explain stability changes

📚 Part 1: Understanding Atomic Models

1. Before the discovery of subatomic particles, atoms were thought to be indivisible. Which scientist's discovery first challenged this idea?

Ernest Rutherford (nucleus)

J.J. Thomson (electrons)

James Chadwick (neutrons)

Niels Bohr (electron shells)

2. Radioactive decay occurs because:

Atoms want to become smaller

Unstable nuclei release energy to become more stable

Electrons are too heavy

Atoms are trying to gain more protons

3. Explain in 2-3 sentences how the discovery of electrons, protons, and neutrons changed our understanding of atomic structure.

🧮 Part 2: Half-Life Calculations

4. A radioactive sample has 800 grams initially. After 5 years, 200 grams remain. What is the half-life of this substance?

Half-life = _________ years

5. Carbon-14 has a half-life of 5,730 years. If a fossil starts with 100 grams of Carbon-14, how much will remain after 11,460 years?

Amount remaining = _________ grams

6. Look at the decay graph below (imagine a curve showing exponential decay from 1000 to 0 over 4 half-lives). If the substance shown has a half-life of 2 hours, what amount would remain after 6 hours?

125 units

250 units

500 units

750 units

✏️ Part 3: Extended Response

7. Explain why unstable atoms undergo radioactive decay and how this process helps them achieve stability. Include the role of the neutron-to-proton ratio in your answer.

8. Extension Activity: Research and explain how knowledge of half-life is used in one real-world application (e.g., carbon dating, medical imaging, nuclear power). Describe both benefits and potential risks.