Lecture 17

Lecture 17 - T opics for the day Administrative stuff Quest...

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Topics for the day Administrative stuff Quest problems Valence bond theory sp Hybridization sp 2 Hybridization sp 3 Hybridization More hybridization possibilities Lone pairs Multiple bonds Administrative stuff Blackboard gradebook “My Grades” in the left menu. ALEKS, Quest, and exam 1 grades uploaded Exam Two is next Wednesday Mar 9th, 7 - 9 pm, WEL 3.502. If you are expecting to take a makeup, watch for an email from Susan confirming you are on our list. If you haven’t heard from her by Wednesday, send her an email. Help Office hours DrRuth: Tue 2 pm, Fri 4 pm Susan: Mon 2 pm, Wed noon, Fri 3 pm Exam preparation Susan exam review Tue (3/8) 6–7 pm. WEL 2.304 Sample exam posted this Friday. Wed next week working problems from homeworks/sample exam 1 2 3 Monday, February 28, 2011

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Quest Homework 98% of the class attempted HW3 Class average was 88% Here are the problems that people are finding harder: A. two pairs of electrons and one lone electron B. three pairs of electrons and one lone electron C. one pair of electrons and three lone electrons D. five lone electrons E. four pairs of electrons iClicker Time The Lewis dot structure for an isolated nitrogen atom has [He] 2s 2 3p 3 2s 2p A. BF 4 B. CH 3 C. CH 3 + D. BrO iClicker Time Which of the following is a radical? Valence electrons 5 + 4 × 7 + 1 = 34; even number 4 + 3 × 1 + 1 = 8; even number 4 + 3 × 1 – 1 = 6; even number 7 + 8 = 15; odd number 4 5 6 Monday, February 28, 2011
A. 3 B. 4 C. 1 D. 2 E. 5 iClicker Time How many non-bonding electrons pairs are there around I in IF 2 ? 7 + 2 × 7 + 1 = 22; 11 electron pairs Valence electrons I F F • • •• I is one of those exceptions to the octet rule. It’s in the “3rd row or higher, where d orbitals are available. So it can take more than 8 electrons. A. B. C. iClicker Time Which structure is most feasible for sulfur dioxide? D. E. Which have the right number of electrons? 6+6+6 = 18; 9 electron pairs Valence electrons 8 e pairs < octet on S FC(O) = 6–6 = 0 FC(S) = 6–6 = 0 FC(O) = 6–6 = 0 Of these, which satisfy the octet rule or are exceptions to it? Of these, which has the lowest formal charges on the atoms? S O O • • S O O •• S O O • • S O O •• S O O • • F. S O O • • 8 e pairs 8 e pairs FC(O) = 6–6 = 0 FC(S) = 6–5 = +1 FC(O) = 6–7 = –1 Although example B has 10 electron pairs, S is n 3, so it is a valid exception. FC(O) = 6–6 = 0 FC(S) = 6–6 = 0 FC(O) = 6–6 = 0 S O O S O O • • FC(O) = 6–6 = 0 FC(S) = 6–5 = +1 FC(O) = 6–7 = –1 I just used formal charge arguments to show the most likely structure of SO 2 from the two valid Lewis structures.

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