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Unformatted text preview: Version PREVIEW Exam 2 JOHNSON (53755) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. LDE Ranking Bonding Trends 004 001 10.0 points The following molecules are composed of hy- drogen(s) bound to another atom, X. Rank the HX bonds in terms of decreasing polar- ity: LiH , NH 3 , BH 3 , HF. 1. LiH > NH 3 > BH 3 > HF 2. NH 3 > BH 3 > HF > LiH 3. HF > LiH > NH 3 > BH 3 correct 4. NH 3 > HF > BH 3 > LiH 5. BH 3 > HF > LiH > NH 3 Explanation: Note that all of the bonds within both NH 3 , BH 3 are identical to each other and the fact that there are multiple bonds does not change the polarity of the individual bonds. The EN for LiH , NH 3 , BH 3 , HF are 1.2, 0.8, 0.2, 1.8, respectively. Arranged from greatest to least: HF > LiH > NH 3 > BH 3 . LDE Identifying Bonds 002 002 10.0 points Which of the following exhibits non-polar bonds in a polar molecule? 1. O 3 correct 2. C 2 H 4 3. BI 3 4. CS 2 5. SiCl 4 Explanation: Ozone (O 3 ) is the only polar molecule composed of non-polar bonds. The other molecules are all symmetrical and therefore non-polar. LDE VSEPR Molecular Geometry 003 003 10.0 points In a molecule of the form AB 2 U x where A is a central atom, B is a bonded atom, and U is an unbonded electron pair, what value of x would yield a non-polar molecule that is not hypervalent? 1. 2 2. correct 3. 4 4. 1 5. 3 Explanation: Having 2 identical bonded atoms and 0 non- bonding electrons would correspond to linear molecular geometry and be non-polar. Hav- ing 1 or 2 non-bonding electron pairs would correspond to angular molecular geometry and be polar. Having 3 or 4 non-bonding electron pairs would be hypervalent. LDE VSEPR Molecular Geometry 004 004 10.0 points Which one of the compounds listed below is NOT expected to exhibit bond angles dis- torted from expected VSEPR values by un- bonded electron pairs? 1. SCl 4 2. NH 3 3. O 3 4. H 2 O 5. I 3 correct Explanation: All of the choices except I 3 have asymmet- rically placed non-bonding electron pairs on their central atoms and thus have distorted Version PREVIEW Exam 2 JOHNSON (53755) 2 bond angle. I 3 has three non-bonding elec- tron pairs in equatorial positions and thus has a single bond angle of exactly 180 . LDE VB Hybridization 003 005 10.0 points Which of the following statements concerning valence bond theory is/are true? I) Hybridizing one 2 s orbital with three 2 p orbitals would produce four sp 3 orbitals. II) When a 2 s orbital is hybridized with a single 2 p orbital, there will be a single unhybridized 2 p orbital left to form a bond with. III) Among the types of hybrid orbitals we have learned about, the minimum amount of s-character for a hybrid or- bital is 1/6 th ....
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This note was uploaded on 03/04/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.
- Spring '07