4.5 Nuclear equations
9 exam questions worth 18 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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A nucleus emits an alpha particle. What happens to its mass number and atomic number?
Choose one answer.
Correct Not quite: the answer is Mass number −4, atomic number −2
Mark scheme
A: Mass number −4, atomic number −2
Model answer
Mass number −4, atomic number −2 (A).
Which type of decay does not change the mass number or the atomic number of the nucleus?
Choose one answer.
Correct Not quite: the answer is Gamma
Mark scheme
C: Gamma
Model answer
Gamma (C).
Complete the equation: ^{238}_{92}\text{U} \rightarrow\; ^{?}_{?}\text{Th} + ^{4}_{2}\text{He}. State the mass number and atomic number of the thorium nucleus.
Mark scheme
mass number = 238 − 4 = 234 (1); atomic number = 92 − 2 = 90 (1)
Model answer
Mass number = 238 − 4 = 234. Atomic number = 92 − 2 = 90. The thorium nucleus is ^{234}_{90}\text{Th}.
Polonium-210 (atomic number 84) decays by alpha emission to form an isotope of lead (atomic number 82). Write the nuclear equation, giving the mass number of the lead.
Mark scheme
lead mass number = 210 − 4 = 206 (1); equation with polonium on the left (1); lead-206 and alpha particle on the right with correct numbers (1)
Model answer
^{210}_{84}\text{Po} \rightarrow\; ^{206}_{82}\text{Pb} + ^{4}_{2}\text{He}
Carbon-14 decays by beta emission: ^{14}_{6}\text{C} \rightarrow\; ^{?}_{?}\text{N} + ^{0}_{-1}\text{e}. State the mass number and atomic number of the nitrogen nucleus.
Mark scheme
mass number = 14 (1); atomic number = 6 + 1 = 7 (1)
Model answer
The mass number stays at 14. The atomic number is 6 − (−1) = 7. The nitrogen nucleus is ^{14}_{7}\text{N}.
Describe what happens inside the nucleus during beta decay.
Mark scheme
a neutron changes into a proton (1); and an electron which is emitted as the beta particle (1)
Model answer
A neutron changes into a proton and an electron. The electron is emitted from the nucleus as the beta particle.
A nucleus emits a gamma ray. Explain why the mass number and the atomic number do not change.
Mark scheme
a gamma ray has no mass (1); and no charge / is not a particle with protons or neutrons (1)
Model answer
A gamma ray has no mass and no charge, so no protons or neutrons are lost, and the mass number and atomic number stay the same.
Explain why the atomic number of a nucleus goes up by one when it emits a beta particle.
Mark scheme
a neutron changes into a proton and an electron (1); the electron is emitted (1); so there is one more proton in the nucleus, and the atomic number is the number of protons (1)
Model answer
A neutron changes into a proton and an electron, and the electron is emitted. The nucleus has one more proton, and the atomic number is the number of protons.
(Edexcel) Sodium-22 ( ^{22}_{11}\text{Na} ) decays by positron emission. State the mass number and atomic number of the nucleus that is formed.
Mark scheme
mass number = 22 (1); atomic number = 10 (1)
Model answer
A proton changes into a neutron, so the mass number stays at 22 and the atomic number goes down by 1, to 10 (neon-22).
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