Nuclear equations Revision Notes for AQA GCSE Physics

Nuclear equations

What are nuclear equations?

Nuclear equations show what happens when unstable nuclei break down through radioactive decay. These equations must always balance - this means the total mass and charge stay the same before and after the decay.

chatImportant

Nuclear equations must always balance - the total mass numbers and atomic numbers must be equal on both sides of the equation. This is a fundamental law of nuclear physics.

There are three main types of nuclear radiation:

Alpha particles (α)
Beta particles (β)
Gamma rays (γ)

Alpha decay

Alpha decay happens when an unstable nucleus gives out an alpha particle. An alpha particle is the same as a helium nucleus - it has 2 protons and 2 neutrons.

What changes in alpha decay:

Mass number goes down by 4
Atomic number goes down by 2
The nucleus becomes a different element

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Worked Example: Uranium-238 Alpha Decay

When uranium-238 undergoes alpha decay:

It becomes thorium-234
An alpha particle is emitted
Gamma radiation may also be given out

The equation looks like this: $^{238}U \rightarrow ^{234}Th + ^4_2\alpha + \gamma$

Check the balance:

Mass numbers: 238 = 234 + 4 + 0 ✓
Atomic numbers: 92 = 90 + 2 + 0 ✓

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The gamma ray has no mass or charge, so it doesn't affect the balancing of the equation. Gamma radiation is pure electromagnetic energy.

Beta decay

Beta decay happens when a neutron in the nucleus changes into a proton and an electron. The electron (called a beta particle) shoots out of the nucleus at high speed.

What changes in beta decay:

Mass number stays the same
Atomic number goes up by 1
The nucleus becomes a different element

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Worked Example: Carbon-14 Beta Decay

When carbon-14 undergoes beta decay:

It becomes nitrogen-14
A beta particle (electron) is emitted

The equation looks like this: $^{14}C \rightarrow ^{14}N + ^0_{-1}e$

Check the balance:

Mass numbers: 14 = 14 + 0 ✓
Atomic numbers: 6 = 7 + (-1) ✓

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The beta particle is written as $^0_{-1}e$ because it has no mass but has a charge of -1.

How to balance nuclear equations

Nuclear equations must balance on both sides. This is a fundamental principle that reflects the conservation of mass and charge in nuclear reactions.

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Balancing Rules for Nuclear Equations:

Mass numbers (top numbers) must add up to the same total
Atomic numbers (bottom numbers) must add up to the same total

Always check both conditions - if either fails, the equation is incorrect!

Balancing tips:

Check the mass numbers add up correctly
Check the atomic numbers add up correctly
Remember alpha particles are $^4_2\alpha$
Remember beta particles are $^0_{-1}e$

Key differences between alpha and beta decay

Type	What's emitted	Mass number change	Atomic number change
Alpha	Helium nucleus ( $^4_2\alpha$ )	Decreases by 4	Decreases by 2
Beta	Electron ( $^0_{-1}e$ )	No change	Increases by 1

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Notice that in alpha decay, both mass and atomic numbers decrease, while in beta decay, the mass number stays the same but the atomic number increases. This is because the nucleus is gaining a proton when a neutron converts to a proton and electron.

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Key Points to Remember:

Nuclear equations must always balance - mass numbers and atomic numbers on both sides must add up the same
Alpha decay: mass number down 4, atomic number down 2
Beta decay: mass number stays same, atomic number up 1
Alpha particles are helium nuclei ( $^4_2\alpha$ )
Beta particles are high-speed electrons ( $^0_{-1}e$ )
Gamma rays have no mass or charge but may be emitted alongside alpha or beta particles

Nuclear equations (AQA GCSE Physics): Revision Notes