2023 TMJC H2 Chem Prelim P2 (Ans)

2023 H2 Chem Prelim P2 (Ans) 1 The Periodic Table shows many interesting and recurring trends. (a) The variation of 1st ionisation energies across Period 4 is similar to that of Period 3. Table 1.1 shows the 1st ionisation energies of six consecutive elements in Period 4. Table 1.1 element Ga Ge As Se Br Kr 1st ionisation energy / kJ mol–1 580 760 950 1140 1350 (i) Explain why the 1 st ionisation energies show a general increase from gallium to krypton. ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ....................... [2] (ii) Using your knowledge of the variations, c omplete Table 1.1 with a suggested value for the first ionisation of selenium. [1] (b) Electrical conductivity is measured in Siemens per meter, S m –1, where a higher value represents higher electrical conductivity. Calcium is a Group 2 metal and has an electrical conductivity of 2.9 × 107 S m–1 while copper is a transition metal and electrical conductivity of 5.9 × 107 S m–1. (i) State the full electronic configuration of copper. ................................ ................................ ................................ ....................... [1] (ii) Explain the difference in electrical conductivity between calcium and copper. ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ....................... [2] 1s22s22p63s23p63d104s1 [1] Copper has a higher electrical conductivity [1] than calcium. ▪ Cu has more mobile electrons (per atom) as there are 3d and 4s electrons in Cu are available for delocalisation, compared to only 4s electrons in Ca. [1] Across the period. • the number of protons increases, hence nuclear charge increases. • the number of electrons