Ca 2+ +Ca 2+ +Ca Ca 2 I 3. the. CaI. CaI 2 correct

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1 Version 1 Practice Exam 2 mccord (4923) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. mportant Message: Please please please remember to RRETLY bubble in your name, uteid, and version number for your exam. We are averaging about 2 students who fail to do this. Think of it as the easiest question on the exam. f you get it wrong, you llget azero when wegrade it. Because Quest is not that user friendly, it will take at least 24 hours to get your avoidable mistake fixed. t is a huge pain in the ass - know that. Please take the time to bubble in your information carefully. Lets have N mistakes on this information please. Thank you so much. m only putting this plea on this practice exam and not on the real exam. So just remember to do it. - Dr. Mcord olt da 6 3 rev 2b 1 1. points Use electron-dot notation to demonstrate the formation of ionic compounds involving the elements a and. 1. None of these 2. a 3 a a 2 2 a a 2 3 a a 2 correct a 3 a 2 a 2 a 2 1. a 2 2 a a 2 3 a a 3 a 3 2 a 3 a gives up two electrons to form the a 2 cation, and the acquires an electron to form anion. Two iodine anions combine with one calcium cation to form an electrically neutral compound: a 2 a 2 Mlib points hoose the pair of names and formulas that

2 Version 1 Practice Exam 2 mccord (4923) 2 do NT match. 1. As 4 6 : tetraarsenic oxide correct 2. S 3 : sulfur trioxide 3. N : nitrogen monoxide 4. l 2 7 : dichlorine heptoxide 5. N 2 5 : dinitrogen pentoxide l 2 7, N 2 5, S 3, and N are all covalent molecules and are named correctly using the appropriate prefixes. As 4 6 is also a covalent compound; appropriateprefixesareusedinthename. tshould be correctly named tetraarsenic hexoxide to indicate the presence of six oxygen atoms in each molecule. LDE Rank Lattice Energy points Rank the crystal lattice energy of the salts Al 2 3, al 2, a, Na, Mg 3 (P 4 ) 2 from least to greatest: 1. Na < a < al 2 < Mg 3 (P 4 ) 2 < Al Na < al 2 < a < Mg 3 (P 4 ) 2 < Al 2 3 correct 3. a < Na < al 2 < Al 2 3 < Mg 3 (P 4 ) 2 4. Mg 3 (P 4 ) 2 < Na < < a al 2 < Al Mg 3 (P 4 ) 2 < Na < al 2 < a < Al 2 3 Sodium fluoride has the least lattice energy because of its small charges, then calcium chloride and calcium oxide with incrementally increasing charges. Both magnesium phosphate and aluminum oxide have identical magnitudes for their charges, but both of the latter are smaller than than their counterparts in the former and consequently have a greater lattice energy. ampion 5 Ex points f the interaction energy between a sodium ion and a chloride ion in table salt is 76 kj/mol, what is the interaction energy between a zinc ion (Zn 2 ) and a sulfide ion (S 2 ) in a hypothetical structure in which the inter-ionic distances are the same as that of Nal? kj/mol kj/mol correct kj/mol kj/mol kj/mol q Zn = 2 q S = 2 q Na = 1 q l = 1 V Nal = 76 kj/mol fristhedistancebetweenthetwoions(the sum of the ionic radii), the energy interaction between ions is given by oulomb s Law: V = q 1q 2 4πǫ r r = q 1q 2 4πǫ V r Nal = r ZnS q Na q l = q Znq S 4πǫ V Nal 4πǫ V ZnS V ZnS = q Znq S V Nal q Na q l (2 )(2 )(76 kj/mol) = (1 )(1 ) = 34 kj/mol, the energy released by the interaction. nternuclear Distance points

3 Version 1 Practice Exam 2 mccord (4923) 3 onsider a potential energy diagram for the interactionofasodiumion(na )withachloride ion (l ). Which of the following statements is/are true? ) Repulsive forces predominate at very small internuclear distances. ) The minimum potential energy occurs when attractive forces are greatest. ) Attractive forces are linearly dependent on the internuclear distance. 1. and 2. only 3. and 4. only correct 5. and 6., and 7. only t is true that repulsive forces predominate at very small internuclear distances; this is the result of the positively charged nuclei electrostatically repelling each other, which occurs despite that fact that sodium ion and chloride ion have opposite charges overall. The attractive forces actually continue to increase as you force the ions closer together, but the repulsive forces increase more, thus offsetting the attractive forces and producing a net increase in potential energy. Thus, the minimum potential energy does not occur at maximum attractive force, but rather at a sweet spot where the sum of attractive and repulsive forces is minimized. Attractive forces are a rectangular hyperbola that asymptotically approach zero as the internuclear distance approacues infinity. Line Drawing to ormula 6 1. points Determine the molecular formula for the molecule: l l l l 2 correct l l 2 l LDE Molecular Polarity points onsider the labeled bonds in the molecule below andrankthem from least tomostpolar in terms of difference in electronegativity. c B e a 1. a < b < c < d < e d 2. d < c < e < a < b correct 3. e < b < d < c < a 4. c < d < e < b < a 5. d < c < a < e < b b N The polarity of a bond is proportional to the difference in electronegativity of the two bonded atoms. The electronegatavity differencesofthelabeledbondsare.5,1.,.1,. and.4, respectively. Lewis dash

4 Version 1 Practice Exam 2 mccord (4923) points Which of the following is the correct Lewis formula for carbon monoxide ()? 1. correct The Lewis formula for carbon monoxide () is available from the atoms: A = 4 2( atom)1 4( atoms) = 12 e ydrogen can form only one bond, so carbon atoms must serve as the central atoms. We place the most symmetrical arrangement possible. The correct dot structure for the molecule should show a complete octet (8 electrons) around the carbon atoms, two electrons around each hydrogen atom, and a total of 12 valence electrons for the entire structure: As can be seen above, the carbon-carbon bond is a double bond. (f using the S = N A rule to determine the dot structure, N = (8 2)(2 4) = 24e and S = 2412 = 12e. This would indicate 6 bonds and correspond to the structure shown above.) Lewis B3 dash 1 1. points Which of the following is the correct Lewis formula for boron trifluoride (B 3 )? Mlib points What kind of carbon-carbon bond is in a molecule of ethylene ( 2 4 )? 1. B 1. ionic 2. single 3. double correct 2. B 4. triple Todrawthedotstructurefor 2 4 wemust first calculate the number of valence electrons 3. B correct

5 Version 1 Practice Exam 2 mccord (4923) 5 4. B B B B 5. 5 The Lewis structure is Xe LDE Resonant Species points Which of the following species exhibit resonance/delocalization? ) N ) 3 ) B 1., 2. only 3. only 9. B 1. B 4., correct 5.,, 6. only 7., The Lewis formula for boron trifluoride (B 3 ) is B hemprin3e T points Draw the Lewis structure of xenon difluoride and give the number of lone pairs of electrons around the central atom correct Both ozone and carbonate have a single pair of resonant electrons and are famous examples of resonant molecules. yanide cannot have resonance since hydrogen can only form a single bond. hemprin3e points onsider the following sets A, B, and [ ] 2 A 1 ) N N [ ] 2 A 2 ) N N

6 Version 1 Practice Exam 2 mccord (4923) 6 B 1 ) As 3 1 ) B 2 ) As 3 2 ) B 3 ) As 3 3 ) of ions. Determine the formal charge on each atom and identify the structure of lowest energy for each set A, B, and. 1. A 2, B 2, 2 2. A 2, B 3, 3 3. A 1, B 1, 1 4. A 1, B 2, 3 5. A 2, B 3, 2 6. A 1, B 2, 1 correct A 1 ) [ N N 1 1 ] 2 A 2 ) [ N N 2 ] 2 B 1 ) As ) 1 B 2 ) As ) B 3 ) As ) hemprin3e T points Which of the following has bond angles slightly less than 19.5? l correct 5. N 2 nly l has four regions of electron density around the central atom; the two lone pairs repel the bonds more, making the bond angle less than Mlib points Which of the following is planar? 1. N 3 2. S N 3 correct P 3 All except the nitrate ion have trigonal pyramidal molecular geometries; the nitrate ion has trigonal planer geometry.

7 Version 1 Practice Exam 2 mccord (4923) 7 hemprin3e T points What is the shape (molecular geometry) of 4? 1. square planar 2. tetrahedral 3. seesaw correct 4. trigonal bipyramidal 5. T-shaped There are five regions of electron density (including one lone pair) around the central atom: hemprin3e T points Which of the following is polar? 1. 5 correct 2. S 6 3. l 4 4. Xe 4 5. Pl 5 Xe 4 and l 4 have 6 RED with two RED being lone pairs situated opposite each other so their effects cancel. nly 5 has an unbalanced number of lone pairs which places one of the polar bonds opposite a lone pair. This unopposed dipole and the lone pair itself make it polar. The others have either 5 or 6 RED and no lone pairs on the central atom. LDE VB ybridization points Which of the following statements concerning hybrid orbitals is/are true? ) ybrid orbitals are energetically degenerate. ) Any element can form sp 3 d 2 hybrid orbitals. ) ybridizing a 2s and a 2p orbital would produce one single sp hybrid orbital. 1. only 2., 3. only correct 4. only 5., 6., 7.,, Statement is true; hybridization was developed as a theoretical framework to explain the energetic degeneracy of bonds in molecules. Statement is false; hybridization involving d orbitals requires access to empty d orbitals, and thus begins in period 3. Statement is false; the number of orbitals used to hybridize is always equal to the number of hybridized orbitals, so using a 2s and a 2p orbital would result in two sp hybrid orbitals. LDE VB Sigma Pi Bonds points ow many different types of sigma (σ) bonds are found in ethanoic acid, 3? n other words, how many different combinations of atomic orbitals are used when forming the σ bonds in ethanoic acid

8 Version 1 Practice Exam 2 mccord (4923) correct 5. none of the above All of the σ bonds found in ethanoic acid are sp 3 1s,sp 3 sp 2,orsp 2 sp 2. LDE VB Sigma Pi Bonds points ow many sigma (σ) and pi (π) bonds are in the Lewis structure for () 4? 1. 8 σ,4 π σ,4 π σ, π σ, π σ,4 π correct hemprin3e points arbon hasavalence offour in nearly allof its compounds and can form chains and rings of atoms. onsider the propyne structure. a b What hybridizations would you expect for the carbon atoms identified by a, b, and c, respectively? 1. sp 3, sp 2, sp 3 2. sp 2, sp 2, sp 3 3. sp 2, sp, sp 4. sp 3, sp, sp 3 c 5. sp 3, sp, sp correct 6. sp 3, sp 3, sp 2 7. sp 2, sp, sp 2 sp 3 sp sp LDE M Diagram points onsider the following molecular orbital diagram: b What are the names of the labeled orbitals, a, b, and c, respectively? 1. π 2p,σ 2p,σ 2s 2. π 2p,σ 2p,σ 2s 3. σ 2p,π 2p,σ 1s 4. σ 2p,π 2p,σ 2s correct 5. σ 2p,π 2p,σ 2s LDE Bond rder points All of the species below have the same bond order except for one of them. Which is it? a c

9 Version 1 Practice Exam 2 mccord (4923) 9 1. Ne 2 2. B 2 correct All of the species have a bond order of.5 except for B 2, which has a bond order of 1.5. Msci points An antibonding orbital is formed when 4. only 5. only 6. only 7. and Li 2 and 2 both have an odd number of electrons and therefore must be paramagnetic. 2 has 16 total electrons, the last two of which must go into separate degenerate π anti-bonding orbitals. 1. a p x -orbital overlaps a p z -orbital. 2.afreeelectronispresentinthemolecule. 3. an s-orbital overlaps a p-orbital. 4. None of these is correct. 5. the overlap of the corresponding atomic orbitals leads to destructive interference. correct n-phase overlap of two atomic orbitals results in molecular bonding orbitals; out-ofphase overlap of two atomic orbitals results in molecular antibonding orbitals. LDE Paramagnetism points Which of the following species is/are paramagnetic? ) Li 2 ) 2 ) 2 1. and 2. and 3., and correct