NJC 4 Physical Periodcity Tutorial Ans

National Junior College SH1 H1 Chemistry 15 Tutorial Physical Periodicity of Elements Periodic Trend -Atomic and Ioni Radii 1 Oxygen reacts with platinum(VI) fluoride, PtF6, as follows. O2 + PtF6 O2+PtF6 It was suggested that xenon should react similarly and in this way, the first noble gas compound was produced. Xe + PtF6 Xe+PtF6 What is the most likely reason for the suggestion being made? A O and Xe have similar atomic radii B O and Xe have similar electron affinities. C O2 and Xe have similar electronic configurations. D O2 and Xe have similar first ionisation energies. N2003/I/3 Ans: D Explanation: In both equations, O2 and Xe loses 1 electron to give O2+ and Xe+ respectively. Hence option D is the best explanation for their similar reactivity. 2 The elements radon (Rn), francium (Fr) and radium (Ra) have consecutive proton numbers in the Periodic Table. What is the order of their first ionisation energies? Least endothermic Most endothermic Least endothermic Most endothermic A Fr Rn Ra B Fr Ra Rn C Ra Rn Fr D Ra Fr Rn N99/III/4; N2002/I/3 Ans: B Explanation: Ionisation energy generally increases across a period and decreases down the group. The most loosely held electron for Rn is in a inner principal quantum shell (n=6) as compared to Fr and Ra (n=7). Hence the largest amount of energy is required to remove the most loosely held electron of Rn. Nuclear charge of Ra is higher than Fr while both atoms have relatively constant shielding effect. Nuclear attraction is stronger for the most loosely held electron of Ra, hence 1st I.E. of Ra > Fr.

National Junior College SH1 H1 Chemistry 16 3 Gaseous particle Xhas a proton number n and a charge of +1. Gaseous particle Y has a proton number of (n+1) and is isoelectronic (has the same number of electrons as) with X. Which statements correctly describe X and Y? 1 X has a larger radius than Y. 2 X requires more energy than Y when a further electron is removed from each particle. Explanation: Problem Solving approach: Suggest two hypothetical example to represent X and Y. X = Na+ and Y = Mg2+ Statement 1: True Across isoelectronic series, ionic radius decreases. Hence X is larger than Y. [Data Booklet shows ionic radius of Na+ (0.095 nm) > Mg2+(0.065 nm)] Statement 2: False More energy is required to remove electrons from Y (ie. Mg2+) than X (ie. Na+) due to the greater nuclear attraction for the most loosely held electron in the higher charged species. Na+(g) Na2+(g) + e 2 nd I.E. of Na = 4560 kJ mol1 Mg2+(g) Mg3+(g) + e 3rd I.E. of Mg = 7740 kJ mol1

National Junior College SH1 H1 Chemistry 17 Periodic Trend Ionisation Energy 4 Table 1 provides data on elements in Period 2 of the Periodic Table. Li Be B C N No. of protons 3 4 5 6 7 Electronic configuration 1s2 2s1 1s 2 2s2 1s 2 2s2 2p1 1s 2 2s2 2p2 1s 2 2s2 2p3 1st ionization energy/ kJ mol1 520 900 801 108