Section 1 of 6Nuclear notation
How it is written
- How it is written The symbol of an element is written with the mass number A at the top left and the proton number Z at the bottom left.
Particle symbols
- Particle symbols Alpha: helium nucleus with A = 4, Z = 2.
- Beta minuselectron with A = 0, Z = −1.
- Beta pluspositron with A = 0, Z = +1.
- GammaA = 0, Z = 0.
Parent and daughter
- Parent and daughter The parent nucleus decays;
- the daughter nucleus is what remains, along with the emitted radiation.
Section 2 of 6The balancing rule
1
Add the mass numbers on the left-hand side of the equation.
2
Add the mass numbers of the products on the right: the totals must be equal.
3
Repeat for the proton numbers, which must also be equal on both sides.
4
Find the unknown daughter by subtraction, then identify the element from its proton number using the periodic table.
5
Check the answer by adding both columns again.
Section 3 of 6Changes for each decay
| Decay | Daughter A | Daughter Z | Example |
|---|---|---|---|
| Alpha | 4 less than parent | 2 less than parent | 23892U → 23490Th + 42He |
| Beta minus | Same as parent | 1 more than parent | 146C → 147N + 0−1e |
| Beta plus | Same as parent | 1 less than parent | 2211Na → 2210Ne + 0+1e |
| Gamma | Same as parent | Same as parent | Excited nucleus → same nucleus + γ |
Section 4 of 6Worked example: radium-226
1
Radium-226 has A = 226 and Z = 88 and decays by alpha emission.
2
The alpha particle takes away 4 from the mass number and 2 from the proton number.
3
The daughter has A = 222 and Z = 86, which is radon.
4
The equation is 22688Ra → 22286Rn + 42He.
5
Check: 222 + 4 = 226 and 86 + 2 = 88, so the equation balances.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Nucleon number | The total number of protons and neutrons, also called the mass number. |
| Proton number | The number of protons in the nucleus, also called the atomic number. |
| Parent nucleus | The unstable nucleus that undergoes decay. |
| Daughter nucleus | The nucleus produced by the decay. |
| Balanced equation | One where the totals of mass number and proton number are equal on both sides. |
Section 6 of 6Exam technique
1
Balancing only the mass numbers and forgetting the proton numbers.
2
Writing the alpha particle as 4 and 4 instead of A = 4, Z = 2.
3
Putting the proton number on the top: A is on top and Z is below.
4
Forgetting that in beta minus decay the electron has Z = −1, so the daughter gains one proton.