Exam 2-solutions - Version 152 – Exam 2 – sparks –...

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Unformatted text preview: Version 152 – Exam 2 – sparks – (51150) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points How many non-bonding electron pairs are around I in IF − 2 ? 1. 2 2. 1 3. 3 correct 4. 5. 4 Explanation: Iodine has seven valence electrons. Flourine has seven valence electrons. Each flourine atom will form a covalent bond by sharing one of iodine’s electrons. This leaves iodine with 5 electrons plus the additional electron that gives the molecule a net negative charge. That makes six non-bonding electrons around iodine, or three pairs. I F b b b b b b F b b b b b b b b b b b b 002 10.0 points Use VSEPR theory to predict the molecular geometry of the molecule HCN. 1. None of these 2. tetrahedral 3. trigonal-bipyramidal 4. linear correct 5. trigonal-planar 6. octahedral 7. trigonal-pyramidal 8. bent or angular Explanation: The Lewis structure for HCN is H b b C b b b b N b b b b or C N b b H Although there is an octet of electrons around C, six electrons are combined to form a triple bond. The two areas of high elec- tron density around the central atom make the molecular geometry linear. 003 10.0 points A molecule has five areas of high electron density around the central atom. One of these is a lone pair and the other four are bonded pairs. What is the hybridization of the central atom? 1. sp 3 2. sp 2 3. sp 3 d correct 4. sp 5. sp 3 d 2 Explanation: The hybridization is sp 3 d because the molecule has 5 regions of high electron den- sity and has trigonal bipyramidal electronic geometry. 004 10.0 points Give the formula for chromium(III) iodide. 1. Cr(III)I 2. CrI 3 correct 3. CrI 4. Cr 3 I Explanation: The chromium(III) iodide is an ionic com- pound because Cr is a transition metal and I is a nonmetal. The (III) after Cr indicates that it has a +3 charge. I is a Group VIIA Version 152 – Exam 2 – sparks – (51150) 2 element having 7 valence electrons. When I ionizes, it gains one e − to obtain the stable 8 valence electron configuration. Cr +3 and I + combine to form the neutral compound CrI 3 . 005 10.0 points Rank the crystal lattice energy of the fol- lowing salts from greatest to least: MgBr 2 , KNO 3 , SrS, LiF, CaI 2 . 1. SrS > CaI 2 > MgBr 2 > LiF > KNO 3 2. SrS > MgBr 2 > CaI 2 > KNO 3 > LiF 3. SrS > MgBr 2 > CaI 2 > LiF > KNO 3 correct 4. KNO 3 > SrS > MgBr 2 > CaI 2 > LiF 5. SrS > CaI 2 > MgBr 2 > KNO 3 > LiF Explanation: Strontium sulfide has the greatest lattice energy because it has the largest charges on its constituent ions, +2 and -2. Magnesium bromide and calcium iodide have charges of +2 and -1, but calcium iodide has larger inter- ion distance and thus less lattice energy. Like- wise, lithium fluoride and potassium nitrate have identical charges, but both potassium ion and the nitrate polyatomic ion are sig- nificantly larger than their counterparts and therefore have less lattice energy....
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This note was uploaded on 04/03/2012 for the course CHEM 56920 taught by Professor Sparks during the Spring '12 term at University of Texas.

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Exam 2-solutions - Version 152 – Exam 2 – sparks –...

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