exam2_solutions - Version 256 – Exam 2 – Sutcliffe...

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Unformatted text preview: Version 256 – Exam 2 – Sutcliffe – (53770) 1 This print-out should have 32 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. THIS EXAM IS FOR DR. SUTCLIFFE’S T-TH CLASS ONLY!! 001 10.0 points Which of the following pairs of atomic orbitals could not combine to produce a σ bond? 1. two p orbitals 2. two sp 2 orbitals 3. two s orbitals 4. All of the given combinations can produce a σ bond, provided that the atomic orbitals are lined up properly. correct 5. an s orbital and a p orbital Explanation: 002 10.0 points An antibonding orbital is formed when 1. an s-orbital overlaps a p-orbital. 2. a p x-orbital overlaps a p z-orbital. 3. a free electron is present in the molecule. 4. the corresponding atomic orbitals are out of phase. correct 5. None of these is correct. Explanation: In-phase overlap of two atomic orbitals re- sults in molecular bonding orbitals; out-of- phase overlap of two atomic orbitals results in molecular antibonding orbitals. 003 10.0 points Which of the following is the correct Lewis formula for oxygen difluoride (OF 2 )? 1. b b b b b b b b b b F O F 2. F b b b b b b b b O F 3. b b b b b b b b b b b b F O F 4. F b b b b b b b b b b b b O F 5. b b b b b b b b b b b b b b b b F O F correct 6. b b b b b b b b b b b b b b F O F 7. b b b b F O F 8. b b b b b b b b F O F 9. b b b b b b b b b b b b b b b b b b F O F 10. F b b O F Explanation: The Lewis formula for oxygen difluoride (OF 2 ) is b b b b b b b b b b b b b b b b F O F 004 10.0 points What is the number of shared electrons in the Lewis dot structure for CS 2 ? 1. 8 correct 2. 3 3. 4 4. 5 5. 6 Explanation: To draw the dot structure for CS 2 we must first calculate the number of valence electrons available from the atoms: The number of available valence electrons is 1 × 4 (from C) + 2 × 6 (from S) = 16 e − . We choose the least electronegative element as the central atom (carbon in this case) and place the other atoms symmetrically around Version 256 – Exam 2 – Sutcliffe – (53770) 2 it. The correct dot structure for the molecule should show a complete octet (8 electrons) around each atom and a total of 16 valence electrons for the entire structure: C · · · · S · · · · S There are four bonds in the structure. Each bond consists of two electrons, so there are eight shared electrons in the structure. (If using the S = N- A rule to determine the dot structure, N = 8 × 1 + 8 × 2 = 24 e − and S = 24- 16 = 8 e − . This would indicate 4 bonds and corre- spond to the structure shown above.) 005 10.0 points A free radical is ? chemical species with ? . 1. a stable; a lone pair of electrons 2. a low energy; an unpaired electron 3. an unstable; an unpaired electron cor- rect 4. a reactive; a full octet of electrons Explanation: Free radicals are very energetic and reactive particles that have an unpaired electron....
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This note was uploaded on 09/09/2009 for the course CH 302 taught by Professor Mccord during the Spring '09 term at University of Texas-Tyler.

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exam2_solutions - Version 256 – Exam 2 – Sutcliffe...

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