Practise Nuclear equations. 15 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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What happens to the mass number and to the atomic number of a nucleus when it emits an alpha particle?
Mass number falls by 4; atomic number falls by 2.
Explain how the equation shows that emitting a neutron does not change the charge of the nucleus.
The atomic number stays at 2, because the neutron's atomic number is 0.
In a balanced nuclear equation, what must be true about the mass numbers on each side of the equation?
The total mass number is the same on both sides.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
(a) Which symbol represents an alpha particle? Tick (✓) one box.[1]
\({}^{4}_{2}\mathrm{He}\)
\({}^{0}_{-1}\mathrm{e}\)
\({}^{1}_{0}\mathrm{n}\)
\(\gamma\)
(b) Which symbol represents a beta particle? Tick (✓) one box.[1]
\({}^{4}_{2}\mathrm{He}\)
\({}^{0}_{-1}\mathrm{e}\)
\({}^{1}_{0}\mathrm{n}\)
\(\gamma\)
(c) What happens to the mass number and to the atomic number of a nucleus when it emits an alpha particle?[2]
(d) What happens to the mass number and to the atomic number of a nucleus when it emits a gamma ray?[1]
Show the answer and mark scheme
(a)Answer: \({}^{4}_{2}\mathrm{He}\)
(b)Answer: \({}^{0}_{-1}\mathrm{e}\)
(c)Answer: Mass number falls by 4; atomic number falls by 2.
the mass number decreases by 4
the atomic number decreases by 2
(d)Answer: Neither changes.
neither changes / both stay the same
Question 2Medium7 marks
Radium-226 decays by emitting an alpha particle. The equation for this decay is: \({}^{226}_{88}\mathrm{Ra} \rightarrow {}^{x}_{y}\mathrm{Rn} + {}^{4}_{2}\mathrm{He}\)
(a) Determine the values of x and y in the equation.[2]
(b) Strontium-90, \({}^{90}_{38}\mathrm{Sr}\), decays by emitting a beta particle. The nucleus formed is an isotope of yttrium (Y). Write a balanced nuclear equation for this decay.[3]
(c) Explain why the mass number does not change when a nucleus emits a beta particle.[2]
beta particle shown as \({}^{0}_{-1}\mathrm{e}\) on the right-hand side
yttrium with mass number 90
yttrium with atomic number 39
(c)Answer: A neutron turns into a proton, so the total number of protons and neutrons is unchanged.
a neutron in the nucleus changes into a proton (and a high-speed electron is emitted)
so the total number of protons and neutrons stays the same
Question 3Hard7 marks
Some very unstable nuclei decay by emitting a neutron. A helium-5 nucleus decays in this way: \({}^{5}_{2}\mathrm{He} \rightarrow {}^{4}_{2}\mathrm{He} + {}^{1}_{0}\mathrm{n}\)
(a) Explain how the equation shows that emitting a neutron does not change the charge of the nucleus.[1]
(b) Explain why neutron emission always produces an isotope of the same element.[2]
(c) Compare the changes to the mass number and the atomic number of a nucleus caused by alpha decay, beta decay, gamma emission and neutron emission.[4]
Show the answer and mark scheme
(a)Answer: The atomic number stays at 2, because the neutron's atomic number is 0.
the atomic number (number of protons) stays at 2 / the neutron has an atomic number (charge) of 0
(b)Answer: The number of protons is unchanged (same element) but there is one fewer neutron (different isotope).
the number of protons (atomic number) does not change, so it is the same element
the number of neutrons (mass number) decreases by 1, so it is a different isotope