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Exam 2-solutions - Version 273 Exam 2 Sutcliffe(53550 This...

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Version 273 – Exam 2 – Sutcliffe – (53550) 1 This print-out should have 34 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 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. 36 correct 2. 28 3. 44 4. 30 5. 64 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) = 36 002 10.0 points When calcium reacts with chlorine, the reac- tion involves a 1. transfer of electrons from Ca to Cl. cor- rect 2. transfer of electrons from Cl to Ca. 3. creation of electrons. 4. sharing of electrons between Ca and Cl. Explanation: 003 10.0 points In our study of chemistry, free radicals 1. usually result in the heterolytic cleavage of chemical bonds. 2. are highly reactive and unstable chemical species with an unpaired electron. correct 3. are chemical species characterized by a reactive lone pair of electrons. 4. are a stablizing force for the ozone layer. 5. are wacky chemical species with strange political beliefs. Explanation: Free radicals are very energetic and reactive particles that have an unpaired electron. 004 10.0 points Bonding orbitals 1. are less stable than anti-bonding or- bitals. 2. are filled after anti-bonding orbitals. 3. hold all valence electrons. 4. are lower in energy than anti-bonding orbitals correct 5. hold non-bonding electrons. Explanation: Bonding orbitals are lower in energy and more stable than anti-bonding orbitals. 005 10.0 points Is the molecule IF + 4 polar? Iodine (I) may ac- cept up to 10 or 12 electrons. 1. It cannot be determined from the infor- mation given. 2. No
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Version 273 – Exam 2 – Sutcliffe – (53550) 2 3. Yes correct Explanation: 006 10.0 points Consider the Lewis electron dot diagram X · · ·· · · · · ·· O · · · · ·· O - for the polyatomic ion XO 2 , which has a charge of negative one. Assuming both oxygen and X follow the octet rule, the unknown element X is probably in group 1. VIA. 2. VIIA. correct 3. IVA. 4. VA. Explanation: There are a total of 20 valence electrons in this structure. Each oxygen atom contributes 6 valence electrons, for a total of 12 electrons from oxygen. One electron is contributed by the negative charge on the molecule. This leaves seven valence electrons that must come from the X atom, indicating that this atom must be located in group VIIA. 007 10.0 points Which of the following is the best description of ionic bonding?
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