WJEC Chemistry for AS Level: Revision Workbook

(b) Ⱦ deflected towards positive plate, ɀ not deflected, positron deflected towards negative plate similar amount to Ⱦ . (2 for all three correct, 1 for two correct.) (c) Ƚ particles are blocked by glass bottle so are contained (1) but once in the body are very ionising and destroy/damage cells/biological molecules (1). (d) Tracers to follow biological molecules around the body (e.g. iodine for thyroid function) / radiotherapy to kill cancerous cells (e.g. cobalt-60). Q9 (a) 1 mark for correct protons and electrons, 1 mark for correct neutrons. 234 U 235 U 238 U Number of protons 92 92 92 Number of neutrons 142 143 146 Number of electrons 92 92 92 (b) (i) Th , 230, 90 (ii) 4 half-lives (1), 1/16th remains (1), 3.125 × 10 −4 % (1). Q10 (a) Ƚ , Ⱦ − , Ⱦ − (b) The half-lives for decay of 228 Ra and 228 Ac are much shorter than that of 232 Th (1). 228 Ra and 228 Ac decay as fast as they are produced so do not build up (1). Q11 (a) (i) He nucleus / He 2+ (ii) Causes mutations / cancers / ionises DNA. (iii) Incorrect (1) as gamma radiation could also be emitted as it doesn’t affect the atomic or mass numbers (1). (b) Two half-lives (1) 0.55 g (1). Q12 (a) Removed from a different shell (1) closer to the nucleus with no shielding OR greater effective nuclear charge (1). (b) Nitrogen has more protons / greater nuclear charge (1). Greater attraction holding electron (1). (c) Sixth electron of oxygen is in the second shell (1) so it has greater shielding / further from the nucleus (1). Q13 (a) Arrow pointing upwards from I to H. (b) Arrow pointing downwards from F to H. (c) Arrow pointing upwards from I to A. (d) E = 2.179 × 10 −18 J (1); f = 3.287 × 10 15 (1); wavelength = 91.26 nm (1). Q14 (a) Ne, Mg (b) ɐ ɐ ɐ ɐ ɐ 1s 2 2s 2 2p 6 3s 0 (c) Sodium (1). Outer electron in potassium is further from the nucleus and shielding is more which overcomes greater nuclear charge (1). (d) Sodium, magnesium, neon (1). Neon is highest as electron removed from different shell, closer to nucleus with much less shielding (1). Magnesium is greater than sodium as it has a greater nuclear charge with similar shielding and electron similar distance from nucleus (1). Q15 (a) Li (g) r Li + (g) + e – [Must show state symbol] (1). (b) Helium has a greater nuclear charge than hydrogen (1) but outer electrons of both are the same distance from the nucleus / in the same shell with the same (no) shielding (1). (c) Outer electron of nucleus is in a different shell to helium (1) further from nucleus with greater shielding which overcomes the greater nuclear charge (1). (d) 200–480 kJ mol −1 (1). Ionisation energy decreases down group so must be lower than Li (1). (e) 1100–1370 kJ mol −1 (1). Outermost electron in oxygen is paired, and in nitrogen it is unpaired (1). Electron–electron repulsion in oxygen reduces ionisation energy below the value for nitrogen (1). Unit 1 Practice questions: Answers | 173 Unit 1 Answers