New 21st Century Chemistry (2nd Edition) Suggested answers to in-text activities and unit-end exercises 1 © Jing Kung. All rights reserved . Topic 6 Unit 23 Suggested answers to in-text activities and unit-end exercises Topic 6 Unit 23 Practice P23.1 (page 4) 1 a) b) CS 2 follows the ‘octet rule’. SF 4 does not follow the ‘octet rule’. 2 a) b) Dative covalent bond c) No. P23.2 (page 7) SiF 4 SCl 2 PH 3 Electron diagram 3-D structure Shape of molecule tetrahedral V-shape or bent shape trigonal pyramidal P23.3 (page 12) HCN When using the electron pair repulsion theory, double bonds can be counted as single bonds. Thus, the carbon atom can be viewed as having two pairs of electrons in its outermost shell. The two electron pairs repel each other. They must be at opposite ends of a straight line in order to be as far apart as possible. Thus, HCN is a linear molecule. HCHO
New 21st Century Chemistry (2nd Edition) Suggested answers to in-text activities and unit-end exercises 2 © Jing Kung. All rights reserved . Topic 6 Unit 23 P23.4 (page 15) 1 Buckminsterfullerene has a simple molecular structure. Weak van der Waals’ forces exist between the C60 molecules. The molecules can slide over each other easily. Hence buckminsterfullerene is soft and slippery. 2 Balls of carbons are very small and not linked to each other, appearing like powder. 3 Van der Waals’ forces exist betwee n molecules of buckminsterfullerene. Such forces also exist between molecules of petrol. Thus, molecules of buckminsterfullerene and petrol mix together easily. Diamond and graphite have giant covalent structures. They are insoluble in petrol because the atoms are held together by strong covalent bonds and it is very difficult to separate the atoms. Discussion (page 4) Not agree. Oxygen is in the second period of the periodic table. It cannot form compounds with more than 8 electrons in the outermost shell of its atom. Chemistry Magazine (page 15) Carbon nanotubes — new material with superior properties 1 Some points students may raise: ․ CNTs may enter the municipal water system; ․ CNTs may be harmful; ․ CNTs may have long-term effects; ․
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- Fall '14