MCQ:
1. B 2. D 3. B 4. A 5. B 6. D 7. C 8. B 9. B 10. D
Structured Qn
1. Sample I and II are isotopes of the same element. Some students highlighted Sample III and Sample IV, a conclusion drawn based on the Periodic Table. The question was vague, so all of these answers are accepted.
2. 0.014x204 + 0.241x206 + 0.221x207 + 0.524x208 = 207.24 = 207 (3 sf)
1. B 2. D 3. B 4. A 5. B 6. D 7. C 8. B 9. B 10. D
Structured Qn
1. Sample I and II are isotopes of the same element. Some students highlighted Sample III and Sample IV, a conclusion drawn based on the Periodic Table. The question was vague, so all of these answers are accepted.
2. 0.014x204 + 0.241x206 + 0.221x207 + 0.524x208 = 207.24 = 207 (3 sf)
3. Atomic structures should not have any brackets or charges. Electronic structures, on the other hand, should have them. A common error is putting the charge when the questions asks for the number of electrons gained or lost. Students should respond by stating "1 electron lost" instead of "+1", or "1 electron gained" instead of "-1".
A trend that could be observed here is that the number of electrons gained or lost is either the group number, or 8-group number.
4. This is a problem for a few students who miscalculated the number of neutrons. Students are reminded that the group number determines the number of valence electrons, and ions with the same charge are likely to be in the same group - the exception being the transition metals.
5. 0.000229x206 + 0.00000628x207 + 0.000275x208 + 0.00997x209 + 0.00360x210 = 209.36 = 209 (3sf)
6. Similarity between nuclei of isotopes: same number of protons
Differences between the nuclei of isotopes: different mass number, different number of neutrons
[Reject answers that refer to the number of electrons, since the question asks about the nuclei]
7. (a) The electronic configuration for X will not be given as it is outside the syllabus. It is used here to sensitize students to the fact that the method of generating teh electronic configuration taught is limited to the first 20 elements.
(b) W, X and Y are metals because they ahve 1, 2 or 3 valence electrons.
(c) X is a metal so it loses electrons. When it loses its valence electrons, the number of shells decreases by 1 and the ion gains a charge based on the number of electrons lost.
(d) 50% of each. 0.