Radioactivity
4 marks · NormalRadon-222 is a radioactive gas found in some rocks. It decays by emitting an alpha particle.
Complete the nuclear equation for this alpha decay:
How do the atomic number and mass number of the daughter nucleus compare to those of the radon nucleus after the alpha emission?
Radon-222 is an isotope of radon. State what is meant by the term isotope.
Explain, in terms of neutrons and protons, why some isotopes, like radon-222, are radioactive.
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(a) · must show 218, 84, Polonium symbol
(b) Mass number decreases by 4; atomic number decreases by 2. · must show mass number -4, atomic number -2
(c) Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. · must show same protons, different neutrons
(d) Some isotopes are radioactive because the number of neutrons is too great or too few for nuclear stability, causing them to decay. · must show unstable neutron:proton ratio, decay to become stable
Common mistakes: Incorrect balancing of nuclear equation; Incorrect definition of isotope
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Marking points
A1 (a) · 1 mark · Correctly balances the nuclear equation: .
B1 (b) · 1 mark · Describes decrease in mass and atomic numbers after alpha emission.
C1 (c) · 1 mark · Defines isotope as atoms with same number of protons, different neutrons.
D1 (d) · 1 mark · Explains that instability is due to an unsuitable ratio of protons and neutrons.
Worked solution
(a) The missing nucleus is .
(b) Mass number decreases by 4 (222 → 218), atomic number by 2 (86 → 84).
(c) Isotopes of an element have the same number of protons but different numbers of neutrons.
(d) Some isotopes like radon-222 are radioactive because they have an unstable combination of neutrons and protons; the neutron to proton ratio is not suitable for stability.