THE STABILITY OF ISOTOPES
2 marks · Normal| Isotope | Number of protons | Number of neutrons |
|---|---|---|
| Neon-20 | 10 | 10 |
| Neon-22 | 10 | 12 |
Based on the data in the table, explain how Neon-20 and Neon-22 differ in terms of their nuclear stability.
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Neon-20 and Neon-22 have the same number of protons but different numbers of neutrons. Neon-20's neutron to proton ratio is 1:1, which is particularly stable for light nuclei. Neon-22 has more neutrons, which may make it less stable, but both isotopes of neon are actually stable. In general, a change in the neutron number affects nuclear stability; too many or too few neutrons may cause instability.
Also accept: Both are stable, but adding neutrons can affect stability for other elements.
Common mistakes: Saying all isotopes are unstable; Confusing stability with chemical reactivity
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Marking points
B1 · 1 mark · References difference is in number of neutrons/neutron:proton ratio.
B2 · 1 mark · States stability is affected by neutron:proton ratio.
Worked solution
Both isotopes of neon have 10 protons, but Neon-22 has two more neutrons than Neon-20. The neutron to proton ratio is important in nuclear stability; for light elements, a ratio of about 1:1 is most stable, as in Neon-20. Adding extra neutrons may make the nucleus less stable in some elements, but both isotopes of neon are stable.