HW4 - padilla (tp5647) – Homework 4 – Sutcliffe –...

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Unformatted text preview: padilla (tp5647) – Homework 4 – Sutcliffe – (53770) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. READ THIS: Note that SOME of these questions require you to understand expanded or incomplete octets and/or VSEPR theory in order to do them. You may find it advisable to wait until this is covered in class before submitting them, but you should look at them before class. 001 10.0 points How many unshared (non-bonded) pairs of electrons are in NF 3 ? 1. thirteen 2. no pairs 3. twenty 4. ten correct 5. one 6. three 7. four 8. two Explanation: The total number of valence electrons is N 1 × 5 e − = 5 e − P 3 × 7 e − = 21 e − 26 e − and the Lewis structure is N b b F b b b b b b F b b b b b b F b b b b b b 002 10.0 points How many valence electrons must be shown in the dot formula for the C 3 H 8 N 2 O molecule? 1. 64 2. 28 3. 36 correct 4. 44 5. 30 Explanation: To find the total number of valence elec- trons available for the dot formula we sum the number of valence electrons in each atom of the molecule. Carbon has 4 valence electrons and there are 3 C atoms. Hydrogen has 1 valence elec- trons and there are 8 H atoms. Nitrogen has 5 valence electrons and there are 2 N atoms. Oxygen has 6 valence electrons and there is 1 O atom. Total valence e − = 4 × 3 (C atom) + 1 × 8 (H atom) + 5 × 2 (N atom) + 6 × 1 (O atom) = 36 003 10.0 points NOTE: This question assumes you follow the octet rule; do not use an expanded octet. The Lewis dot structure of BrO + 3 has how many total electrons and how many shared electrons? 1. 24; 6 2. 25; 7 3. 24; 8 correct 4. 25; 8 5. 26; 8 6. 26; 6 7. 25; 6 8. 26; 7 Explanation: padilla (tp5647) – Homework 4 – Sutcliffe – (53770) 2 The total number of valence electrons is 1 × 7 e − (for Br) + 3 × 6 e − (for O)- 1 e − (from + 1 charge) = 24 e − Br is the central atom, with the O atoms ar- ranged around it. Br will have an incomplete octet if we show one shared pair of electrons (a single bond) with each O, so one double bond is necessary: Br O b b b b b b O b b b b b b O b b b b + 004 10.0 points From what column must atom A come in the Lewis dot structure for CH 3 A? The central atom is carbon. It is bonded to three hy- drogen atoms and single-bonded to A. Both carbon and A follow the octet rule. 1. II 2. IV 3. VII correct 4. III 5. VI 6. VIII 7. V Explanation: Since A follows the octet rule, it must have three lone pairs of electrons around it: C H H H A · · · · ·· This structure has 14 valence electrons. H 3 × 1 e − = 3 e − C 1 × 4 e − = 4 e − A 1 × x e − = x e − (7 + x ) e − 14 = 7 + x , so A has 7 electrons, and A comes from group VII....
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This note was uploaded on 02/03/2009 for the course CH 301 taught by Professor Sutcliffe during the Spring '08 term at University of Texas-Tyler.

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HW4 - padilla (tp5647) – Homework 4 – Sutcliffe –...

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