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Exam 2-solutions.pdf

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Department
Chemistry
Course
CH 301
Professor
Sutcliffe
Semester
Spring

Description
Version 188 – Exam 2 – mccord – (51600) 1 This print-out should have 35 questions. Multiple-choice questions may continue on Cl I Cl the next column or page – find all choices before answering. Cl ICl3has 3 I Cl single bonds and 2 lone 001 3.0 points pairs on I. There are 5 regions of HED re- Rank the following atoms in terms of decreas-sulting in a trigonal bipyramidal electronic ing atomic radius. geometry and T-shaped molecular geometry. 1. Na, N, O, Mg, F 003 3.0 points 2. F, O, N, Na, Mg Which of the following best describes the range of atomic radii? 3. F, O, N, Mg, Na 1. 0.4 to 3 A correct 4. Na, Mg, N, O, F correct 2. 1to15 A 5. F, Mg, Na, O, N 3. 0.05 to 1 A Explanation: 4. 1to100 A As you move down the periodic table ˚ atomic radius increases because the shielding 5. 5to10 A e▯ects of inner electrons reduces the e▯ective nuclear charge experienced by outer shell elec-. 10 to 30 A trons. As you move across the periodic table Explanation: the radius decreases because electrons are be- Atomic radii vary from 30 pm (He) to 300 ing added to the same electronic shell (and pm (Fr). 1 A= 10 ▯10 m=1 0pm,ohe thus do not add additional shielding e▯ects) ˚ range of atomic radii is 0.3 to 3 A. while the number of protons increases. Na, being farthest left and down the table, would 004 3.0 points be the largest while F, being farthest right and up the table, would be the smallest. The bond order denotes 1. the order of filling of bonding vs. anti- 002 3.0 points bonding orbitals. The predicted geometry of I3l would be 2. an estimate of the polarity or dipole mo- ment of a bond. 1. T-shaped. correct 3. the order that orbitals are filled in electron 2. trigonal bipyramidal. configurations. 3. trigonal pyramidal. 4. an estimate of the strength of a bond. correct 4. trigonal planar. 5. the pattern in which Lewis dot structures 5. linear. of atoms combine to form bonds. Explanation: Explanation: Bond order is an estimate of the stability of Version 188 – Exam 2 – mccord – (51600) 2 the bond and hence the strength of the bond. Highest charge densities due to small size. 005 3.0 points 007 3.0 points Rank the following atoms and ions What would be the electron geometry of the + 2+ ▯ 3+ nitrogen atom in nitric oxid2, N O? Li , Be , He, H , B in order of decreasing size. 1. octahedral 3+ 2+ + ▯ 2. linear correct 1. B ,Be ,He,Li ,H 3+ 2+ + ▯ 3. trigonal planar 2. B ,Be ,Li ,He,H 3. H ,He,Li + ,Be2+ ,B3+ correct 4. trigonal bipyramidal 4. H ,Li +,He,Be 2+ ,B3+ 5. tetrahedral ▯ + 2+ 3+ Explanation: 5. He, H ,Li ,Be ,B The central nitrogen atom in2N Ohasonly Explanation: 2regionsofely.trondensit We are comparing ions with the same num- ber of electrons (that have noble gas con- 008 3.0 points figurations): 2 total and 2 valence in this How many sigma (▯)andpi( ▯)bondsarein case. The number of protons in the ion is the the Lewis structure for CHCCH2COOH? biggest determinate of the size when electron number is constant. Since there are no in- 1. 11 ▯,1 ▯ ner shell electrons to shield the nucleus, the e▯ective nuclear charge is just the charge of 2. 9 ▯,3 ▯ correct the nucleus. The greater the e▯ective nuclear charge, the stronger the attraction between 3. 8 ▯,2 ▯ the protons and the electrons, and thus the smaller the radii. 4. 10 ▯,2 ▯ H > He > Li > Be 2+ > B 3+ 5. 9 ▯,2 ▯ Explanation: 006 3.0 points If the following crystallize in the same type 009 3.0 points of structure, which has the highest lattice Which of the following is the correct Lewis energy? formula for hydrogen cyanide (HCN)? 1. KBr 1. HCN 2. LiF correct 2. H CN correct 3. KCl 4. KF 3. H CN 5. LiCl 4. Explanation: HCN Version 188 – Exam 2 – mccord – (51600) 3 What values are expected for the O▯Cl▯O 5. H CN bond angles? 1. 129.5 6. HCN ▯ 2. 109.5 correct 7. HCN 3. 100.5 8. HCN 4. 145.5 ▯ 9. HCN 5. 180.0 6. 209.5 10. HCN Explanation: Explanation: All of the oxygen atoms are equivalent (res- onance forms) so there should be only one The Lewis formula for hydrogen cyanide O▯Cl▯Ob nd;totc (HCN) is ▯ H CN 109.5 . 010 (part 1 of 2) 3.0 points 012 3.0 points What is the shape of the ClO ion? 3 Which of the following is a radical? 1. trigonal pyramidal correct 1. BrO correct ▯ 2. tetrahedral 2. CH 3 3. trigonal planar 3. BF▯ 4 4. octahedral 4. CH 3 5. square pyramidal Explanation: ▯ Odd valence e count. 6. trigonal bipyramidal 013 (part 1 of 2) 3.0 points Explanation: The resonant Lewis structures are Draw the Lewis structure for ONCl. How ▯ ▯▯ ▯ ▯▯ many single bonds, double bonds, triple O O bonds, and unshared pairs of electrons are ▯ ▯ ▯ ▯ on the central atom, in that order? O Cl O O Cl O 1. 0, 2, 0, 0 ▯ ▯▯ O ▯ ▯ 2. 0, 1, 1, 0 ▯ ▯ O Cl O 3. 4, 0, 0, 0 The chlorate ion is trigonal pyramidal. 4. None of these 011 (part 2 of 2) 3.0 points 5. 1, 0, 1, 0 Version 188 – Exam 2 – mccord – (51600) 4 of high electron density make the electronic 6. 3, 0, 0, 1 geometry trigonal-planar and the molecular geometry bent. 7. 2, 1, 0, 0 8. 1, 1, 0, 1 correct N 9. 2, 0, 0, 2 O Cl 10. 0, 0, 1, 1 015 3.0 points Explanation: Lewis structure of ONCl = ? Which of the following is the best represen- Ohs6olNhs5- tation of the compound potassium sulfide? lence electrons and Cl has 7 valence electrons. The total number of valence electrons in the 1. None is appropriate because potassium molecule is sulfide is a covalent compound. ▯ ▯ 6+5+7=18 2+ ▯ 2. K , 2 S The Lewis structure for ONCl is ▯ ▯2▯ 3. 2K+ , S correct Cl NO ▯ ▯3▯ and the central atom has one single bond, one 4. 3K2+ , 2 S double bond, and one lone pair. ▯ ▯▯ + 014 (part 2 of 2) 3.0 points 5. K , S ▯ ▯ Determine the molecular geometry of the 2+ 2▯ molecule ONCl. 6. K , S 1. bent or angular correct Explanation: The best drawing will show the valence elec- 2. octahedral trons, the charges, and the appropriate ratio of ions for 2 S. 3. trigonal-planar 4. None of these 016 3.0 points Among the following molecules, which has the strongest bonds? 5. tetrahedral 1. NO2 6. linear 2. SO 7. trigonal-bipyramidal 2 3. CO2 8. trigonal-pyramidal Explanation: 4. CH2ClF moleculargeometry of ONCl = ? The central atom N has 2 bonding pairs 5. N2correct and 1 lone pair of electrons. The three areas Version 188 – Exam 2 – mccord – (51600) 5 6. O3 019 2.0 points 7. O2 Which of the following compounds has an ionic bond? Explanation: The atoms in N2are joined by triple bonds. Triple bonds are the strongest of the covalent 1. SO 3 bonds. 2. NaCl correct 017 3.0 points 3. HCl Classify the molecule Si4r . 4. CO 2 1. nonpolar molecule with nonpolar bonds Explanation: 2. polar molecule with polar bonds Ionic bonds form when two elements re- 3. polar molecule with nonpolar bonds act that have very di▯erent electronegativ-
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