📖 In-Depth Theory
Writing Nuclear Equations
Nuclear equations show radioactive decay using nuclear notation.
Rules for BALANCING nuclear equations:
MASS NUMBERS must balance — top numbers sum the same on both sides.
ATOMIC NUMBERS must balance — bottom numbers sum the same on both sides.
ALPHA PARTICLE symbol: ⁴₂He (or ⁴₂α)
BETA PARTICLE symbol: ⁰₋₁e (or ⁰₋₁β)
GAMMA RAY: represented by γ — no change to mass or atomic number
Alpha decay:
Parent nucleus → daughter nucleus + alpha particle
Mass number decreases by 4. Atomic number decreases by 2.
Beta decay:
Parent nucleus → daughter nucleus + beta particle
A neutron becomes a proton + electron: ¹₀n → ¹₁p + ⁰₋₁e
Mass number unchanged. Atomic number increases by 1.
Alpha and Beta Decay Examples
ALPHA DECAY EXAMPLE:
Radium-226 decays by alpha emission:
²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He
Check: mass numbers: 226 = 222 + 4 ✓
Atomic numbers: 88 = 86 + 2 ✓
Radium (88) → Radon (86) — atomic number decreases by 2, so element changes.
BETA DECAY EXAMPLE:
Carbon-14 decays by beta emission:
¹⁴₆C → ¹⁴₇N + ⁰₋₁e
Check: mass numbers: 14 = 14 + 0 ✓
Atomic numbers: 6 = 7 + (−1) ✓
Carbon (6) → Nitrogen (7) — atomic number increases by 1.
GAMMA EMISSION:
Often follows alpha or beta decay — nucleus releases excess energy as gamma ray.
No change to mass number or atomic number.
No separate nuclear equation needed — just add + γ.
Effect on the Nucleus
ALPHA DECAY:
Mass number: decreases by 4
Atomic number: decreases by 2
Result: new element (two places lower in periodic table)
BETA DECAY:
Mass number: unchanged (a neutron converts to a proton + electron)
Atomic number: increases by 1
Result: new element (one place higher in periodic table)
GAMMA EMISSION:
Mass number: unchanged
Atomic number: unchanged
Result: same element, just releases energy
PATTERN TO REMEMBER:
Alpha → lose 4 mass, lose 2 charge
Beta → same mass, gain 1 charge
Gamma → no change to nucleus
EXAM STRATEGY:
Always check both mass AND atomic numbers balance.
Use the periodic table to identify the daughter element from its new atomic number.
⚠️ Common Mistake
In beta decay, the MASS NUMBER stays the same — a neutron turns into a proton plus an electron. The atomic number INCREASES by 1 (one more proton). Students often think beta decay is like alpha and reduces mass number.