Nuclear equations Revision Notes for AQA GCSE Physics Combined Science

Nuclear equations

Nuclear equations show what happens when unstable atoms break down through radioactive decay. These atoms release particles and energy to become more stable.

What are nuclear equations?

Nuclear equations represent radioactive decay processes. When unstable nuclei decay, they can emit three types of radiation:

Alpha particles - helium nuclei
Beta particles - high-speed electrons
Gamma rays - electromagnetic radiation (energy only)

chatImportant

Conservation Rule: The most important rule is that mass and charge must be conserved. This means the total mass number and atomic number must be the same on both sides of the equation.

Alpha decay

In alpha decay, an unstable nucleus loses an alpha particle. An alpha particle is actually a helium nucleus containing 2 protons and 2 neutrons.

What happens during alpha decay:

The mass number decreases by 4 (loses 4 particles)
The atomic number decreases by 2 (loses 2 protons)
The nucleus becomes a different element
Gamma radiation may also be emitted (this carries away energy but doesn't change mass or atomic numbers)

lightbulbExample

Worked Example: Uranium-238 Alpha Decay

Uranium-238 decays to thorium-234:

$^{238}U_{92} \rightarrow ^{234}Th_{90} + ^{4}He_{2}$

Uranium has mass number 238 and 92 protons
After alpha decay: thorium has mass number 234 and 90 protons
The alpha particle has mass number 4 and 2 protons

Checking conservation:

Mass: $238 = 234 + 4$ ✓
Charge: $92 = 90 + 2$ ✓

Beta decay

In beta decay, a neutron inside the nucleus changes into a proton. This process creates a high-speed electron (called a beta particle) that shoots out of the nucleus.

infoNote

During beta decay, the total number of particles in the nucleus stays the same, but one neutron transforms into a proton plus an electron. The electron is ejected from the nucleus as the beta particle.

What happens during beta decay:

A neutron becomes a proton + electron
The mass number stays the same (same total particles)
The atomic number increases by 1 (gains one proton)
The nucleus becomes a different element
The electron is emitted as a beta particle

lightbulbExample

Worked Example: Carbon-14 Beta Decay

Carbon-14 decays to nitrogen-14:

$^{14}C_{6} \rightarrow ^{14}N_{7} + ^{0}e_{-1}$

Both have mass number 14 (no change in total particles)
Carbon has 6 protons, nitrogen has 7 protons (increased by 1)
A beta particle (electron) is emitted

Checking conservation:

Mass: $14 = 14 + 0$ ✓
Charge: $6 = 7 + (-1)$ ✓

Key differences

Type of decay	Mass number change	Atomic number change	Particle emitted
Alpha	Decreases by 4	Decreases by 2	Alpha particle (helium nucleus)
Beta	No change	Increases by 1	Beta particle (electron)
Gamma	No change	No change	Gamma ray (energy only)

Balancing nuclear equations

When writing nuclear equations, it's essential to follow systematic checking procedures to ensure accuracy.

chatImportant

Always check these three things:

Mass numbers add up on both sides
Atomic numbers add up on both sides
The correct symbols are used for particles

For alpha particles, use the symbol $^{4}He_{2}$ or $^{4}\alpha_{2}$ with mass number 4 and atomic number 2.

For beta particles, use the symbol $^{0}e_{-1}$ or $^{0}\beta_{-1}$ with mass number 0 and atomic number -1.

bookmarkSummary

Key Points to Remember:

Nuclear equations must balance - mass numbers and atomic numbers must be equal on both sides
Alpha decay reduces both mass number (by 4) and atomic number (by 2)
Beta decay keeps mass number the same but increases atomic number by 1
Gamma radiation only carries away energy - no change to mass or atomic numbers
Conservation laws always apply - nothing is lost, just rearranged or converted

Nuclear equations (AQA GCSE Physics Combined Science): Revision Notes