Year 10 Science · Unit 2 · Lesson 21

Inside the Atom's Nucleus, Nuclear Stability

Challenge Worksheet

Name

Date

Class

Learning Goals

Identify and correct five scientific errors about nucleons, isotopes and nuclear stability.
Explain why each error is a common misconception and write the correct version.
Apply nuclide notation and the band of stability to justify your corrections precisely.

Go Deeper

Find the mistakes

A student wrote these five statements in their revision notes

"Isotopes of an element are different elements because they have different masses, so carbon-14 is a different substance from carbon-12."
"The mass number tells you the number of neutrons in the nucleus, so ²³₁₁Na has 23 neutrons."
"Gravity is the force that holds the protons and neutrons together inside the nucleus."
"The more neutrons you add to a nucleus, the more stable it always becomes."
"Some isotopes of uranium (Z = 92) are perfectly stable and never decay."

1. Identify the error in statement 1 and write the correct definition of isotopes, explaining why they are the same element.

Challenge 1 mark

2. Correct statement 2. Explain what the mass number really counts, and work out the correct number of neutrons in ²³₁₁Na.

Challenge 1 mark

3. Correct statement 3. Name the force that actually holds the nucleus together and explain why gravity plays no meaningful role at this scale.

Challenge 1 mark

Go Deeper (continued)

4. Correct statement 4. Explain why both too few and too many neutrons cause instability, using the idea of the neutron-to-proton ratio and the band of stability.

Challenge 2 marks

5. Correct statement 5. Explain why every element heavier than bismuth (Z = 83) is radioactive, referring to the two competing forces inside the nucleus.

Challenge 2 marks

Show What You Know

1. Helium-4 (⁴₂He) is stable but uranium-238 (²³⁸₉₂U) is radioactive. In two or three sentences, compare the two nuclei and explain why one is stable and the other is not, referring to the strong nuclear force, electrostatic repulsion and the number of protons.

Challenge 3 marks

Wrap Up

Why is it useful for Australian scientists at ANSTO to understand exactly which nuclei are stable and which are not?