DESCRIPTIVE INORGANIC CHEMISTRY QUIZ II February 28, 2013 INSTRUCTIONS: PRINT YOUR NAME > NAME. SHOW YOUR WORK FOR POSSIBLE PARTIAL CREDIT THE LAST PAGE IS A Periodic Table Work 5 of these (100 pts) R = 0.08206 lit-atm/mol-k 1 (20) R = 8.3145 J/mol-K 2 (20) h = 6.626 X 10-34 J-s 3 (20) c = 2.9979 X 10 8 m/s 4 (20) J = (kg-m 2 )/s 2 5 (20) 6 (20) ` (100) TOTAL(100)
1. Draw a valid Lewis structure for the following species. Assign formal charges to ions. Indicate the shape according to VSEPR in the blank. (a) NO 2 - (b) ClO 4 -- c) BrCl 5 Shape Shape Shape (d) OSCl 2 (e) BrCl 3 2- (f) CO 3 (S atom central) Shape Shape Shape
2. (a) Draw a resonance structure for O 2 ClF (the Cl atom is the central atom) that obeys the octet rule and assign formal charges to the all atoms. (b) Draw a resonance structure that has more reasonable formal charges. (c) Draw the shape of the molecule using wedges and dashed lines. What is approximate shape of the molecule? (d) Is the molecule polar? Clearly explain why or why not.
3. Give a short answer or explanation for each of the following: (a) What are the strongest intermolecular forces in each of the following molecules? (A Lewis structure will probably help.) BF 3 HBr NH 3 SO 2 (b) Describe how band theory of metallic bonding explains the conductivity or lack of conductivity in conductors, insulators, and semi-conductors. You may use a drawing as part of your answer. (c) What two properties of a pair of metals are most important for efficient alloy formation? (d) Describe the difference between ferromagnetism and antiferromagnetism. (e) Why do both ferromagnetism and antiferromagnetism convert to normal paramagnetism upon heating above a certain temperature?
4. (a) Sketch the most efficient way to pack a single layer of metal atoms. What is the symmetry of this layer? (b) Polonium is the only metal that crystallizes in a simple cubic lattice. Why don t more metals crystallize with this structure? (c) What are the coordination numbers for a metal atom in: 1) A body centered cubic arrangement? 2) cubic closest packed arrangement? 3) hexagonal closest packed arrangement? (d) Cubic closest packed can be described as repeating hexagonal layers or as a unit cell. What is the repeat pattern on the hexagonal layers for cubic closest packed? Another way to describe cubic closest packed is a unit cell which for cubic closest packed is face centered cubic. Describe where the atoms are located in the cell and using fractional occupancies of the atoms derive the number of atoms in the unit cell.
5. Answer the following questions about ionic compounds. The melting points of the Group 2 oxides are given in the table below along with the crystal structure type. Compound Melting point ( C) Crystal structure type BeO 2578 ZnS (wurtzite) MgO 2830 NaCl CaO 2900 NaCl SrO 2530 NaCl BaO 1973 NaCl (a) The trend in melting point for CaO, SrO, BaO is smoothly decreasing from the Ca compound to the Ba compound. How is this explained? (b)beo adopts a different structure form the others. Why is this? (c) Of the structures that crystallize in the sodium chloride structure, MgO seems to go against the trend of the other three. Based on the trend MgO should have a higher melting point than CaO. How can the lower than expected melting point for MgO be explained? (d) The ZnS Zinc blende structure is shown below (The zinc atoms are shown with tetrahedral coordination and the other atoms are sulfur atom: (1) What is the coordination number for Zn? (2) The coordination number for sulfur is not fully shown on the photo, what is the actual coordination number for S in this structure. (3) Derive, using fractional occupancies, the number of Zn and the number of S in the unit cell.
6. Below is the bond triangle from Chapter 5. Note the horizontal axis is the average electronegativity. The vertical axis is the difference in electronegativity. Electronegativities Na K O F N Al S Pb Mg Cl 0.9 0.8 3.5 4.0 3.0 1.5 2.44 1.7 1.23 2.8 (a) What type of bonding is predicted for MgCl 2 according to the triangle? (c) What type of bonding is predicted for Na according to the triangle? (c) What type of bonding is predicted for SO 2 according to the triangle? (d) Lead forms two Chlorides PbCl 2 (melting point 500 C) and PbCl 4 (melting point -15 C) What are the bonding types in the two lead chlorides according to the melting points? PbCl 2 PbCl 4 (e) Which lead chloride has the bonding type predicted by bond triangle?