THE STABILITY OF ISOTOPES
3 marks · EasyDefine what an isotope is.
The most common isotope of oxygen is written as . How many neutrons does it have in its nucleus?
Explain, in terms of neutrons and protons, how isotopes of the same element are similar and how they differ.
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(a) Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons.
(b) 8
(c) Isotopes of the same element have the same number of protons but different numbers of neutrons.
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Marking points
B1 (a) · 1 mark · Defines isotope as atoms of the same element with different numbers of neutrons
B1 (b) · 1 mark · Correctly calculates number of neutrons as 8 for
B1 (c) · 1 mark · States that isotopes have the same number of protons but different numbers of neutrons
Worked solution
a) Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
b) Oxygen-16 has a mass number (A) of 16 and an atomic number (Z) of 8. Number of neutrons = A - Z = 16 - 8 = 8.
c) Isotopes have the same number of protons (so they are the same element) but different numbers of neutrons.