Chemistry Unit 9 — Nuclear Chemistry.
This unit covers radioactive decay, half-life and fission and fusion — essential concepts for Chemistry. Use our interactive study games to test your understanding, or review questions in traditional format below.
Pick a mode. Play.
Answer questions as fast as you can. 2 minutes on the clock. Build streaks for bonus points!
Don't want to play?
Review the questions traditionally. Click to expand.
Questions loading...
Focus on understanding.
Focus on understanding core concepts before memorizing details. Use the game modes to test yourself repeatedly — spaced repetition is proven to boost long-term retention.
This unit covers radioactive decay, half-life and fission and fusion — essential concepts for Chemistry. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Radioactive Decay
Radioactive decay is the spontaneous breakdown of an unstable nucleus, releasing particles or energy. Students must know the three main types: alpha (α), beta (β), and gamma (γ) decay, including what is emitted and how the atomic number and mass number change. Balancing nuclear equations by conserving both mass number and atomic number is a core exam skill.
Key Points
- Alpha decay: emits ²⁴He; mass number decreases by 4, atomic number decreases by 2
- Beta decay: emits ⁰₋₁e; mass number stays the same, atomic number increases by 1
- Gamma decay: emits high-energy photons (⁰₀γ); no change in mass number or atomic number
- In any nuclear equation, the sum of mass numbers and the sum of atomic numbers must be equal on both sides
Uranium-238 undergoes alpha decay. Write the nuclear equation and identify the daughter nucleus.
Start with ²³⁸₉₂U and subtract a ⁴₂He (alpha particle): 238 − 4 = 234 for the new mass number, and 92 − 2 = 90 for the new atomic number. Atomic number 90 is Thorium, so the daughter nucleus is ²³⁴₉₀Th, giving the equation ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He.
2 Half-Life
Half-life is the time required for exactly half of a radioactive sample to decay. Students must be able to calculate the remaining amount of a substance after a given number of half-lives using the formula: remaining amount = initial amount × (1/2)ⁿ, where n is the number of half-lives elapsed. Half-life is constant for a given isotope and is not affected by temperature, pressure, or chemical state.
Key Points
- After each half-life, exactly half of the remaining radioactive nuclei have decayed
- Formula: A = A₀ × (1/2)ⁿ, where n = total time ÷ half-life
- After 1 half-life: 50% remains; after 2: 25%; after 3: 12.5%; after 4: 6.25%
- Carbon-14 (t½ ≈ 5,730 years) is commonly used in exam contexts for radioactive dating problems
A sample of Iodine-131 has a half-life of 8 days. If you start with 80 g, how much remains after 32 days?
First, find the number of half-lives: 32 days ÷ 8 days = 4 half-lives. Then apply the formula: 80 × (1/2)⁴ = 80 × (1/16) = 5 g. After 32 days, 5 grams of Iodine-131 remain.
3 Fission and Fusion
Nuclear fission is the splitting of a large, heavy nucleus into two smaller nuclei, releasing a large amount of energy; nuclear fusion is the combining of two light nuclei into a heavier nucleus, also releasing energy. Students must know that both processes convert a small amount of mass into energy according to Einstein's equation E = mc². For the exam, know which process powers nuclear reactors (fission) and which powers the sun (fusion).
Key Points
- Fission: a heavy nucleus (e.g., U-235) absorbs a neutron and splits, releasing energy and 2–3 more neutrons (chain reaction)
- Fusion: light nuclei (e.g., hydrogen isotopes deuterium and tritium) combine to form helium, releasing more energy per gram than fission
- Both processes release energy because the products have less mass than the reactants (mass defect); the lost mass becomes energy via E = mc²
- Fission is used in nuclear power plants and atomic bombs; fusion powers stars and is the basis of hydrogen bombs
In a fission reaction, U-235 absorbs a neutron and splits into Kr-92 and Ba-141. How many neutrons are released?
Write the equation: ¹n + ²³⁵₉₂U → ⁹²₃₆Kr + ¹⁴¹₅₆Ba + x¹n. Check mass numbers: 1 + 235 = 236 on the left; 92 + 141 + x on the right. Solving: 236 = 233 + x, so x = 3 neutrons are released. Always verify atomic numbers balance as well: 0 + 92 = 36 + 56 = 92. ✓
Questions, answered.
What is Nuclear Chemistry?
Nuclear Chemistry is Unit 9 of Chemistry, covering radioactive decay, half-life and fission and fusion.
How to study for Chemistry Unit 9?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 25+ review questions across 5 different game modes.