WJEC Chemistry for AS Level: Revision Workbook

Dewi’s answer (a) ض 1s 2 2s 2 2p 3 (b) Ionisation energies increase across a period, so group 1 elements have the lowest ionisation energies. Ionisation energies decrease down the group, so the lowest ionisation energy is the one for sodium. ضض (c) Be will have the greatest ionisation energy because ionisation energies decrease slightly from group 2 to 3. غض (d) I think the second ionisation of magnesium will be about 1300 kJ mol –1 . I have chosen this answer as the second ionisation of magnesium will be slightly larger than the first, so it will be a bit more than half 2187 kJ mol –1 . ضض MARKER COMMENTARY (a) This is the correct electron arrangement. (b) The marks here are for the reasons. The answer identifies the patterns across a period and down a group, and so gains both marks. (c) The correct element is identified; however, the candidate gives a reason rather than an explanation. This answer gains one mark only. (d) The value suggested is within the acceptable range, and the reason given is correct, so it gains both marks. Overall Dewi gains 6 out of 7 marks as he can correctly identify the electron arrangements of different atoms and link these to their ionisation energies. Rebecca’s answer (a) غ 1s 2 2s 2 2p 3 (b) The general trend in the periodic table is low values in the bottom left and high values in the top left. Sodium will therefore have the lowest value. ضض (c) B will have the greatest ionisation energy because ionisation energies generally increase across the period. غغ (d) I estimate the value to be about 1100 kJ mol –1 . I have chosen this answer as the value given is for two electrons, so the value for one will be about half. The second ionisation energy will be slightly higher than the first, and the first ionisation energy in this case will be 1087 kJ mol –1 . ضغ MARKER COMMENTARY (a) This is incorrect – the electrons in the p sub-shell should be unpaired. (b) This is a broad description of the pattern of ionisation energies, and this is just sufficient for the marks. (c) The element is incorrect. The pattern stated is correct, but it does not apply to the comparison between Be and B which is one of the exceptions. (d) The pattern described is correct and gains a mark. The value is too low, however, and doesn’t gain the second mark. Overall Rebecca gains 3 out of 7 marks. Her answer shows some awareness of general patterns but lacks the detail needed to gain higher marks. 1.2: Basic ideas about atoms | 27 Unit 1 Practice questions