2. (10%) Correct answers are given below. Every correct answer gives a student 1⅔=1.666 point. There are no negative points for incorrect answers

Transcription

1 1. (9%) There are 9 correct answers: (0,0), (1,-1), (1,0), (1,1), (2,-2), (2,-1), (2,0), (2,1), and (2,2). Each correct answer gives a student +1 point. All other answers are incorrect. Every incorrect answer gives a student -1 point. Students can get maximum 9 points and minimum 0 points for this question. If the sum of points for student s correct and incorrect answers gives a negative number, the student gets 0 points. Examples: 8 correct answers + 1 incorrect answer = 8-1 = 7 7 points 1 correct answer + 8 incorrect answers = 1-8 = -7 0 points 2. (10%) orrect answers are given below. Every correct answer gives a student 1⅔=1.666 point. There are no negative points for incorrect answers umber of radial nodes umber of angular nodes 1s 0 0 3p x 1 1 4d xy (10%) Schematic plots are given below. Some students may plot additional components to visualize better the 3D features of each orbital. Dotted line represents inner radial nodal planes; they are not essential here. Each of the plots shown below drawn in an appropriate place gives a student 2½ points. Use common sense to decide if the answer is correct or not if the student s answers differ much from the pictures below. 1

2 4. (a) (5%) Because the lattice energy is related to the coulombic attraction between the ions, it is inversely proportional to the distance between the ions. The larger iodide will have the lower lattice energy for a given cation. (b) (4%) ompounds composed of small, highly charged cations, which have highly polarizaing powers, tend to have bonds with considerable covalent character. Mg 2+ is the smaller, more highly charged cation; as a result, MgBr 2 has bonds with greater covalent character than abr does. (c) (6%) The bond strength decreases as the atomic radii increase; thus, the order of bond dissociation energy: l 2 > Br 2 > I 2. In addition, lone pairs repel each other. The repulsion becomes more significant in the case of F 2, because F has smaller radius. This explains why the bond in F 2 is weaker than the bond in l 2 (Br 2 ). 5. (8%) S S S Structure with lowest formal charges are likely to have the lowest energy S 6.(8%) 2-3 > 2 > ; in there is a triple bond and in 2 the - bonds are double bonds. In 2-3, the bond order of - is approximately 1.3. Because the bond length is inversely related to the number of bonds between the atoms; thus, 2-3 > 2 >. bond length: 2- > > bond order :

3 7. (10 points) onsider azidocarbonamide, 2 ()=() 2. A) Draw Lewis structures for two cis- and trans- isomers of azidocarbonamide. trans isomer 1 point cis isomer 1 point B) Predict polarity for these isomers. non polar 1 point polar 1 point ) ow many lone pairs of electrons are there in the Lewis structure? 8 lone pairs 2 points D) What is the approximate bond angle? 120 degrees (or slightly smaller than 120) 2 points E) Describe the hybridizations of all, and atoms in the molecule. 2 ()=() 2 sp3 2 ()=() 2 sp2 2 ()=() 2 sp2 2 ()=() 2 sp2 Minus 1 point for each wrong answer, 2 points total 8.(10 points) The orbital structure of the heteronuclear diatomic molecule is similar to that of 2. A) ow will the fact that the electronegativity of differs from that of affect the molecular orbital energy-level diagram of compared to 2? Energy of atomic orbitals is lower than those of. 2 points B) Draw the molecular orbital energy-level diagram for. 1 point for correct energy levels 1 point for correct labeling 1 point for correct electron filling 3

4 σ 2p * 2p π 2p * σ 2p 2p 2s π 2p σ 2s * 2s σ 2s ) What is the bond order of? B..= ( 7 2 ) / 2 = point D) Is diamagnetic or paramagnetic? 1 unpaired electron paramagnetic 1point E) Indicate which orbital in the molecular orbital energy-level diagram is M. σ 2p 1 point F) Indicate which orbital in the molecular orbital energy-level diagram is LUM. π 2p * 1 point G) In the molecular orbitals, will the electrons have a higher probability of being at or at? 1 point 4

5 9. (20 points) hoose the correct answer for each of the following questions. 1. What is the shape of Al 4? A) tetrahedral D) T-shaped B) trigonal bipyramidal E) square planar ) seesaw 2. What is the shape of Il 4? A) T-shaped D) tetrahedral B) trigonal bipyramidal E) square planar ) seesaw Ans: E 2points 3. All of the following have an angular shape except A) l. B) S 3. ) I 3. D) l 2. E) 2. Ans: 2points 4. Which of the following has bond angles slightly less than 109? A) S 3 B) AsF 3 ) S 2 D) l 2 E) S Ans: B 2points 5. All of the following are polar except A) SF 4 B) l 2 + ) IF 4 D) XeF 4 E) lf 3 Ans: D 2points 6. All of the following are paramagnetic except + A) 2 B) 2 2+ ) 2 D) 2 E) 2 Ans: 2points 7. Which of the following would have the longest bond? A) B 2 B) 2 ) 2 D) 2 E) 2 8. The bond order of + 2 is A) 1 B) 2 ) 3 D) 2.5 E) 1.5 Ans: D 2points 9. Which of the following species has the shortest bond length? A) B) 2+ ) D) E) + Ans: E 2points 10. Which of the following is an n-type semiconductor? A) Si doped with P B) Si doped with B ) GaAs with Ga in excess of As D) Se doped with In E) Ge doped with In 5