Radioactivity
4 marks · EasyThe diagram below shows two isotopes of carbon:
State what is meant by the term "isotope".
Explain how the number of neutrons affects the stability of these two isotopes of carbon.
Give one possible use of a radioactive isotope of carbon.
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(a) Atoms of the same element with the same number of protons but different numbers of neutrons.
(b) Adding more neutrons can make a nucleus unstable. Carbon-14, with 8 neutrons, is less stable and radioactive, while carbon-12, with 6, is stable. · must show states neutron ratio/number and how it affects stability
(c) Carbon-14 is used in radiocarbon dating/labelling in biology/archaeology.
Common mistakes: Confuses isotope with ion; States stability is only about proton count; Lists irrelevant uses
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Marking points
B1 (a) · 1 mark · Gives correct definition of isotope.
B2 (b) · 1 mark · Links neutron number to nuclear stability or instability for carbon-14/carbon-12.
B3 (b) · 1 mark · States carbon-14 is unstable/radioactive, carbon-12 is stable due to neutron number difference.
B4 (c) · 1 mark · States a correct use of a radioactive carbon isotope (e.g. radiocarbon dating).
Worked solution
a) Isotopes are atoms of the same element (same proton number) with different numbers of neutrons. b) The number of neutrons in a nucleus affects its stability. If there are too many (or too few) neutrons for the number of protons, the nucleus may become unstable and radioactive. Carbon-12, with 6 neutrons, is stable. Carbon-14, with 8 neutrons, is unstable and radioactive due to extra neutrons. c) Carbon-14 can be used in radiocarbon dating to estimate the age of formerly living things.