2021 CJC H2 CHEM Prelim P3 Mark Scheme (with comments)

9729/03 CJC JC2 Preliminary Examination 2021 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/03 Paper 3 Free Response September 2021 2 hours Candidates answer on the question paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. At the end of examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 24 printed pages. Catholic Junior College JC2 Preliminary Examination Higher 2 MARK SCHEME

2 9729 CJC Preliminary Examination 2021 Section A Answer all the questions in this section. 1 Fluorine is the most electronegative element and forms many interesting compounds. Antimony, Sb, is in Group 15 of the periodic table and forms two covalent fluorides that exist as simple molecules in gas phase, SbF3 and SbF5. Krypton, Kr, is in Group 18 of the periodic table and its first compound discovered is KrF2. (a) Draw 'dot-and-cross' diagrams showing the electrons (outer shells only) in SbF3, SbF5, and KrF2. Use the VSEPR (valence shell electron pair repulsion) theory to predict their shapes and hence state whether the species is polar or non-polar. [8] ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................