Nuclear Chemistry Worksheet 3 featuring exercises on identifying radioactive particles, completing nuclear equations, and analyzing the decay series of uranium-238 to lead-206.

Let’s go step by step through each part of the worksheet.

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Part 1: Identify as alpha, beta, gamma, or neutron

We need to match symbols and descriptions to the correct type of nuclear decay particle.

1. ₀¹n → This is a neutron (mass number 1, charge 0).
2. ₋₁⁰e → This is an electron emitted from the nucleus — that’s beta decay.
3. ₂⁴He → Helium nucleus — this is an alpha particle.
4. ₀⁰γ → Gamma ray — no mass, no charge — gamma.

Now for the descriptive questions:

5. Nuclear decay with no mass and no charge → That’s gamma.
6. An electron → In nuclear context, this is beta.
7. Least penetrating nuclear decay → Alpha particles are stopped easily — so alpha.
8. Most damaging nuclear decay to the human body → If inside the body, alpha is most damaging because it dumps all its energy in a small area — so alpha.
9. Stopped by skin or paper → Again, alpha.
10. Stopped by aluminum → Beta particles can be stopped by thin metal like aluminum — so beta.

✔ Answers for 1–10:
1. neutron
2. beta
3. alpha
4. gamma
5. gamma
6. beta
7. alpha
8. alpha
9. alpha
10. beta

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Part 2: Complete the nuclear equations

In nuclear reactions, both mass numbers (top) and atomic numbers (bottom) must balance on both sides.

11. ₁₉⁴²K → ₋₁⁰e + ?
- Mass: 42 = 0 + ? → ? has mass 42
- Charge: 19 = -1 + ? → ? has charge 20 → element with atomic number 20 is Calcium (Ca)
→ Answer: ₂₀⁴²Ca

12. ₉₄²³⁹Pu → ₂⁴He + ?
- Mass: 239 = 4 + ? → ? = 235
- Charge: 94 = 2 + ? → ? = 92 → Uranium (U)
→ Answer: ₉₂²³⁵U

13. ₄⁹Be → ₄⁹Be + ?
- Same on both sides? Then the missing particle must have mass 0 and charge 0 → gamma ray (₀⁰γ)
→ Answer: ₀⁰γ

14. ₉₂²³⁵U → ? + ₉₀²³¹Th
- Mass: 235 = ? + 231 → ? = 4
- Charge: 92 = ? + 90 → ? = 2 → Helium nucleus → alpha particle (₂⁴He)
→ Answer: ₂⁴He

15. ₃⁶Li → ₂⁴He + ?
- Mass: 6 = 4 + ? → ? = 2
- Charge: 3 = 2 + ? → ? = 1 → Hydrogen-2? But wait — actually, this is likely producing two helium nuclei? Wait — let’s check:
Actually, lithium-6 splitting into helium-4 and... what’s left? Mass 2, charge 1 → that’s deuterium (hydrogen-2), but in nuclear notation, we write it as ₁²H. However, sometimes this reaction produces two alphas? No — 6Li → 4He + 2H? Yes.
But looking at common reactions: ₃⁶Li → ₂⁴He + ₁²H
So answer: ₁²H (deuterium)

*Wait — let me double-check:*
Left: mass 6, charge 3
Right: He-4 (mass 4, charge 2) + X → X must be mass 2, charge 1 → yes, ₁²H

→ Answer: ₁²H

16. ? → ₅¹⁴²Ba + ₃₆¹Kr + 3 ₀¹n
- Total mass on right: 142 + 91 + 3×1 = 236
- Total charge on right: 56 + 36 + 0 = 92
→ So parent nucleus must be mass 236, charge 92 → Uranium-236 → ₉₂²³⁶U

→ Answer: ₉₂²³⁶U

✔ Answers for 11–16:
11. ₂₀⁴²Ca
12. ₉₂²³⁵U
13. ₀⁰γ
14. ₂⁴He
15. ₁²H
16. ₉₂²³⁶U

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Part 3: Nuclear Decay Series (Uranium-238 to Lead-206)

Look at the diagram. We start at ₉₂²³⁸U and end at ₈₂²⁰⁶Pb.

Each alpha decay reduces mass by 4 and atomic number by 2.
Each beta decay increases atomic number by 1, mass unchanged.

Total change in mass: 238 – 206 = 32 → since each alpha removes 4 mass units → 32 ÷ 4 = 8 alpha particles

Total change in atomic number: 92 – 82 = 10 decrease.

But each alpha decreases atomic number by 2 → 8 alphas would decrease by 16.

But we only decreased by 10 → so some beta decays must have increased the atomic number.

Let x = number of beta decays.

Net change in atomic number = -2*(number of alphas) + 1*(number of betas) = -10

So:
-2(8) + x = -10
-16 + x = -10
x = 6

→ So 6 beta particles

Check:
Start: U-238 (92 protons)
After 8 alphas: lose 16 protons → 92 - 16 = 76
Then 6 betas: each adds 1 proton → 76 + 6 = 82 → which is lead → perfect.

Also, gamma doesn’t change mass or charge — so ignore for counting.

✔ Answers:
17. 8
18. 6

19. Why is lead-206 stable?

Lead-206 has a “magic number” of protons (82) and neutrons (124). Nuclei with magic numbers of protons or neutrons are especially stable. Also, after many decays, it reaches a configuration where the strong nuclear force balances the repulsive forces perfectly — no more decay needed. It’s the end of the chain because it’s energetically favorable and won’t spontaneously change.

Simple version: Lead-206 has just the right mix of protons and neutrons to hold together tightly — nothing wants to break apart or change anymore.

✔ Answer for 19:
Lead-206 is stable because it has a balanced number of protons and neutrons that make its nucleus very tight and unchanging — it doesn’t have extra energy to release, so it doesn’t decay further.

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Final Answer:

1. neutron
2. beta
3. alpha
4. gamma
5. gamma
6. beta
7. alpha
8. alpha
9. alpha
10. beta
11. ₂₀⁴²Ca
12. ₉₂²³⁵U
13. ₀⁰γ
14. ₂⁴He
15. ₁²H
16. ₉₂²³⁶U
17. 8
18. 6
19. Lead-206 is stable because its nucleus has a perfect balance of protons and neutrons, making it unable to decay further — it’s at the lowest energy state possible for that combination.