2020 ACJC Prelim Paper 2 Qns

3 © ACJC2020 9729/02/Prelim/2020 [Turn over Answer all the questions in the spaces provided. 1 The Periodic Table currently used is derived from that proposed in 1869 by Mendeleev who had noticed patterns in the physical and chemical properties of the elements he had studied. (a) (i) The atomic radius of the Period 3 elements decreases from Na to C l. Explain why this is so. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ………………………………………………………………………………...….. ……………………………………………………………………………….…[2] (ii) Write the electronic configurations of the sodium atom and its ion. Na 1s2………………………………… Na+ 1s2………………………………… [1] (iii) Explain the difference in the radius of the sodium atom and the radius of its ion, Na+. ………………………………………………………………………………….[1] (b) (i) Complete Table 1 .1 by describing the acid/base behaviour of Al2O3 and SO3. Provide equation(s) to illustrate the behaviour of each oxide. Table 1.1 oxide acid/base behaviour equation(s) illustrating behaviour of each oxide Al2O3 SO3 [4]

4 © ACJC2020 9729/02/Prelim/2020 [Turn over (ii) State one source of SO2 pollution. ………………………………………………………………………………….[1] (iii) State an environmental consequence of SO2. ………………………………………………………………………………….[1] (c) A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third Periods. The elements and their compounds in these pairs are observed to share similar properties. An example of such a pair is beryllium and aluminium. (i) Draw the dot -and-cross diagram for A lCl3 and state the C l−Al−Cl bond angle. dot-and-cross diagram of AlCl3 [1] bond angle: ………………………………. [1] (ii) Unlike AlCl3 which dimerises to form Al2Cl6, BeCl2 polymerises and exists as long chains in the solid state. Draw a section of one chain with three BeCl2 monomers, showing clearly the bonding within the chain. [1]

5 © ACJC2020 9729/02/Prelim/2020 [Turn over (iii) With a small amount of water, BeC l2 hydrolyses in the same manner as AlCl3. Write an equation for the hydrolysis of BeCl2. ………………………………………………………………………………….[1] [Total: 14]

6 © ACJC2020 9729/02/Prelim/2020 [Turn over 2 This question concerns the chemistry of the halogens and hydrogen halides. (a) Fluorine, F2, and chlorine, Cl2, are halogens that exist as gases at room temperature and pressure. (i) With reference to their structure s and bonding, e xplain why C l2 has a higher boiling point than F2. ………………………………………………………………………………...…. ………………………………………………………………………………...…. ………………………………………………………………………………...…. ………………………………………………………………………………...…. …………………………………………………