130 points on 6 pages + a useful page Circle the element/compound most likely to have the desired property. Briefly explain your choice

Transcription

1 Name Chemistry 35 Spring 212 Exam #2, March 3, minutes 13 points on 6 pages + a useful page 7 1. Circle the element/compound most likely to have the desired property. Briefly explain your choice a) Softest base N 3- Se 2- S 2- P 3- (12 pts) b) Strongest acid in water H 3 AsO 3 H 3 AsO 4 H 3 AsO 2 c) Strongest acid in water [V(OH 2 ) 6 ] 2+ [V(OH 2 ) 6 ] 4+ [V(OH 2 ) 6 ] 5+ d) Most soluble in water LiF LiCl LiBr LiI 2. Using Hard/Soft-Acid/Base theory, determine whether these reactions have equilibrium constants, K, greater than or less than 1. Designate each ion as hard (H) or soft (S). (9 pts) a) 2 PbS + PbO 2 2 PbO + PbS 2 K 1 b) Nb 2 S HgSe Nb 2 Se HgS K 1 c) BaF 2 + HgI 2 BaI 2 + HgF 2 K 1 /21

2 Chem 35, Spring 212, Exam 2 CCM, Page 2 3. Fill in the blanks with the proper element symbols: (3 pts) Sketch the overlap regions of the following combinations of orbitals, all with co-linear z axes, i.e. the two atoms share a common z axis. Classify the interactions as bonding, anti-bonding or non-bonding (no interaction). If the interaction is bonding or anti-bonding indicate if the interaction is, or. (9 pts) a) d xy and d xy b) d xz and p x d) Briefly comment on the relative strengths of sigma, pi, and delta overlaps 5. Draw portions of two close-packed layers and show the relative positions and numbers of octahedral and tetrahedral holes. Clearly indicate the number of octahedral and tetrahedral holes per close-packed atom. (6 pts) /18

3 Chem 35, Spring 212, Exam 2 CCM, Page 3 6. We talked about a number of definitions of acids and bases in class. For the solvent system SbF 5, consider the following. (12 pts) a) Write a balanced chemical equation for the auto-ionization equilibrium by fluoride exchange. Be sure to clearly identify the acidic and basic species. b) Briefly comment on how the solvent system description of acids and bases compares to Lewis acid/base theory and Bronsted-Lowry acid/base theory. c) In this solvent system silver fluoride would be considered (circle one) acidic or basic. d) Write a balanced chemical equation to provide evidence for your choice in c). 7. Shown at right is a unit cell for the mineral cuprite: (12 points) a) Based on the metrics shown, to which of the seven crystal systems does this unit cell likely belong? b) What is the formula unit for this unit cell in terms of Cu and O c) How many of these formula units are there per unit cell? d) I can describe the nickel arsenide structure type as a hexagonal close-packed arrangement of anions with cations in all of the octahedral holes. Please describe cuprite in similar terms. /24

4 Chem 35, Spring 212, Exam 2 CCM, Page 4 8. The molecule ICl 3 has C 2v symmetry. a) Analyze the x, y, and z coordinates of ICl 3 to determine the reducible representation,, for the atoms in the molecule ICl 3. (4 pts) b) Using the character table provided, determine which irreducible representations are normal vibrational modes. (12 pts) (Note: If you have no answer for part a), use = ) C 2v E C 2 (z) v(xz) v(yz) A z x 2, y 2, z 2 A R z xy B x, R y xz B y, R x yz c) and which of those modes are IR- and/or Raman-active. Be sure to indicate how many total bands are expected to be observed. (4 pts) 9. Given the Cartesian coordinates xyz consider the following matrix transformations: (6 pts) For each, i) provide the new Cartesian coordinates after transformation, ii) identify the symmetry operation that was performed, and iii) determine the character of the 3 x 3 matrix. 1 a) b) 1 1 /26

5 Chem 35, Spring 212, Exam 2 CCM, Page 5 1. Consider the hyponitrite ion, NO -. (2 pts) a) In the box provided, generate a well-labeled molecular orbital diagram for NO -. useful info? Orbital potential energy (ev) element 2s 2p N O ON YOUR DIAGRAM b) Clearly indicate which orbitals are the HOMO and/or LUMO. c) Indicate whether NO - is paramagnetic or diamagnetic (circle one) d) Using the diagram you generated in a, determine the likely bond order of i. NO - ii) NO iii) NO + e) What is the most likely position for adding H + to the NO - ion? Explain your answer. /2

6 Chem 35 Spring 212, Exam 2 CCM, Page Generate the MO diagram for the theoretical linear molecule BH 2 by showing the following: a) Determine the point group of the theoretical linear molecule BH 2. (2 pt) b) Using the character table provided (it may or may not be for a point group of the same symmetry as part a) generate the group orbitals of H 2 and indicate the symmetry (i.e. irreducible representation label) of each. Please use z as the bonding axis. (4 pts) E C 2 (z) C 2 (y) C 2 (x) i (xy) (xz) (yz) A g x 2, y 2, z 2 B 1g R z xy B 2g R y xz B 3g R x yz A u B 1u z - B 2u y - B 3u x - c) Indicate the relevant atomic orbitals and their symmetries for the central atom, B. (4 pts) d) In the box provided, generate a well-labeled molecular orbital diagram --be sure to label the orbital levels appropriately and to indicate whether each orbital is bonding, anti-bonding, or non-bonding. (11 pts) Orbital potential energy (ev) element 1s or 2s 2p B H /21

7 Chem 35 Spring 212, Exam 2 CCM, Page 7 Some of the structure types you know Perovskite Nickel Arsenide Sphalerite Wurtzite Rock salt/halite Hexagonal Close-packed Body-Centered Cubic Anti-fluorite Fluorite Diamond Cesium Chloride Simple Cubic Face-centered Cubic Cubic Close-packed A useful table? r + /r - CN