Relative atomic mass
4 marks · NormalUse the information below to answer the questions about isotopes.
Give the definition of isotopes.
State one similarity and one difference between the isotopes and .
Explain why the chemical properties of the two isotopes are the same.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
(b) Similarity: both have 8 protons; Difference: different numbers of neutrons (8 vs 10) or different mass numbers (16 vs 18).
(c) Because they have the same number and arrangement of electrons.
Common mistakes: Stating differences in electron number; Incorrect similarity/difference
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Marking points
B1 (a) · 1 mark · Correct definition of isotopes: same number of protons, different number of neutrons or mass number.
B2 (b) · 1 mark · Correct similarity (same number of protons).
B3 (b) · 1 mark · Correct difference (different mass numbers OR different number of neutrons).
B4 (c) · 1 mark · States that they have the same number/arrangement of electrons, so same chemical properties.
Worked solution
a) Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
b) Similarity: both and have 8 protons. Difference: has 8 neutrons; has 10 neutrons.
c) The chemical properties are the same because they have the same number and arrangement of electrons.