ISM_chapter8_part2

ISM_chapter8_part2 - Chapter 8: Covalent Bonding 371 Write...

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Chapter 8: Covalent Bonding 371 Write the Lewis structures. Then determine the number of lone pair electrons and bonding electrons around each atom. Use the method described in Section 8.8 on page 355 and the solution to Question 52 to determine the formal charges on each atom. (a) The Lewis structure for CH 3 CHO molecule: 18 electrons total. H C C H H O H . . . . Set up the chart: C– C= H O Valence electrons 4 4 1 6 Lone pair electrons 0 0 0 4 Bonding electrons 8 8 2 4 Formal charge 4 – (0 + 4) = 0 4 – (0 + 4) = 0 1 – (0 + 1) = 0 6 – (4 + 2) = 0 H C C H H O H . . . . 0 0 0 0 0 0 0 (b) There are three possible Lewis structures for N 3 ion: 16 electrons total. First structure: Set up the chart: . . . . . . N N N . . N= =N= Valence electrons 5 5 Lone pair electrons 4 0 Bonding electrons 4 8 Formal charge 5 – (4 + 2) = –1 5 – (0 + 4) = +1 . . . . . . . . N N N –1 –1 +1 Second structure: Set up the chart: N N N . . . . . . . . Left-most N Middle N Right-most N Valence electrons 5 5 5 Lone pair electrons 2 0 6 Bonding electrons 6 8 2 Formal charge 5 – (2 + 3) = 0 5 – (0 + 4) = +1 5 – (6 + 1) = –2 N N N . . . . . . . . +1 –2 0
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372 Third structure: Set up the chart: N N N . . . . . . . . Left-most N Middle N Right-most N Valence electrons 5 5 5 Lone pair electrons 6 0 2 Bonding electrons 2 8 6 Formal charge 5 – (6 + 1) = –2 5 – (0 + 4) = +1 5 – (2 + 3) = 0 N N N . . . . .. .. –2 +1 0 The first of these three structures is the best, since the formal charges on each atom are closer to zero. (c) Lewis structure for CH 3 CN molecule: 16 electrons total H C C H H N . . Set up the chart: C H N Valence electrons 4 1 5 Lone pair electrons 0 0 2 Bonding electrons 8 2 6 Formal charge 4 – (0 + 4) = 0 1 – (0 + 1) = 0 5 – (2 + 3) = 0 H C C H H N . . 0 0 0 0 0 0 Reasonable Answer Check: The sum of the formal charges is zero for the neutral molecules and the ionic charge for the charged ion. The atoms with more bonds have more positive formal charges than those with fewer bonds and more lone pairs. 55. Answer: (a) Kr F F F F . . . . . . . . . . . . . . .. . . . . .. .. . . . . 0 0 0 0 0 (b) O Cl O O . . . . .. . . . .. .. . . . . . . . –1 –1 –1 +2 (c) Cl S O Cl O . . .. . . . .. . . . . . . . . . . . 0 0 0 0 0 Strategy and Explanation: Given the formulas of molecules or ions, write the correct Lewis structure and assign formal charges to each atom. Write the Lewis structures. Then determine the number of lone pair electrons and bonding electrons around each atom. Use the method described in Section 8.8 and the solution to Question 52 to determine the formal charges on each atom. (a) Draw the Lewis structures for KrF
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ISM_chapter8_part2 - Chapter 8: Covalent Bonding 371 Write...

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