YIJC 2023 H2 Chem Prelim P2 Worked Solutions (1)

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 28 August 2023 2 hours READ THESE INSTRUCTIONS FIRST This document consists of xx printed pages and x blank pages. For Examiner’s Use 1 / 9 2 / 8 3 / 8 4 / 8 5 / 12 6 / 20 7 / 10 Penalty units significant figures Overall / 75 Write your name and class in the spaces at the top of this page. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid/tape. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question.

©YIJC [Turn over 2 Answer all the questions in the spaces provided. 1 Semiconductors are made from a variety of raw materials. Through a complex process, semiconductor grade silicon of high purity can be produced by refining the raw materials. (a) An unknown element R was studied for its semiconductor properties. The table below shows the ionization energies of element R. Table 1 1st 2nd 3rd 4th 5th 6th 7th Ionisation Energy/kJ mol–1 945 2026 2987 4144 6593 7880 14 990 The principal quantum number of Element R is n. Predict, with explanation, the Group where element R will be found in and complete its electronic configuration. [2] Group: . . . . . . . . . . . . . . . . . . . . . . Electronic configuration: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Group 16 R: ns2np6 Largest energy difference: 14900 – 7880 = 7110 kJ mol-1 Based on the I.E data, the largest difference in energy is between the 6th and the 7th I.E. This means that the 7th electron to be removed is found in the inner shel l, and thus element R has 6 valence electrons (b) Silicon is commonly used in semiconductors. One important raw material for semiconductors is silane (SiH4), which is a key precursor in the production of semiconductor-grade silicon. (i) Draw the dot-and-cross diagram of silane. State the molecular shape about the central Si atom in silane. [2]

©YIJC [Turn over 3 Tetrahedral (ii) Deduce the polarity in silane, giving a reason for your answer. [1] Silane is non -polar, as the dipole moments caused by all Si – H bonds in a tetrahedral ar