Name CHM 115 EXAM #2 Practice Circle the correct answer. (numbers 1-8, 2.5 points each) 1. Which of the following bonds should be the most polar? a. N Cl b. N F c. F F d. I I e. N Br 2. Choose the element that should have the lowest electronegativity. a. K b. Be c. O d. Al e. S 3. Which of the following contains a non-isoelectronic species (ion or atom)? a. Na +, Mg 2+, Ne b. Sc 3+. Ti 4+, V 5+ c. S 2-, Cl -, Ar d. N 3-, O 2-, F - e. all sets are isoelectric 4. Which of the following species has a central atom with sp 3 hybridization? a. SO 2 b. NO - 3 c. CH 4 d. CO 2-3 e. none of the above 5. Which of the following bonds should be the shortest and strongest? a. C=C b. C C c. O=O d. C O e. C _ C 6. Which of the following sets contains the greatest number of bent molecules? a. CO 2, HCN, O 2 b. H 2 S, HCN, CO 2 c. H 2 O, CO, H 2 S d. H 2 S, CO, CO 2 7. Which of the following is a tetrahedral molecule? a. BCl 3 b. SO 2 c. CH 4 d. NH 3 e. I 2 8. Which of the following is a bent molecule? a. BCl 3 b. SO 2 c. CH 4 d. NH 3 e. I 2 Complete the following as directed (point values as indicated). (6 points) 9. Draw the Lewis structures of the following THREE species: CN -, CO, NO + and discuss which should have the shorter / stronger bond.
(6 points) 10. (a) Draw the Lewis structure of ozone (O 3 ) using resonance if needed. (18 points for completion of BOTH parts (a) and (b)) 11. (a) In the spaces provided, do the following for BrF 5 Draw the BEST Lewis structure of this interhalogne molecule and show formal charge calculations for each type of atom Give the names of (a) the electron pair geometry and (b) the molecular shape, (a) (b) Specify the hybridization of the Br AND draw the energy diagram for the hybridized orbitals (you know - the boxes with electrons in them). Is this species polar or nonpolar? Explain. (b) In the spaces provided, do the following BrF 3 Draw the BEST Lewis structure of this interhalogne molecule and show formal charge calculations for each type of atom Give the names of (a) the electron pair geometry and (b) the molecular shape, (a) (b) Specify the hybridization of the Br AND draw the energy diagram for the hybridized orbitals (you know - the boxes with electrons in them). Is this species polar or nonpolar? Explain. 2
(22 points) 12. For the following two species complete the tasks specified below in a - d. i. CH3COOH ii. C 2 H 2 a. Draw the best Lewis structures. b. Specify the hybridization of both the C atoms and the O atom specified in (i) and the C atoms in (ii)? c. Show the energy level diagram for both the C atoms and the O atom in (i) and the C atoms in (ii), fill the diagrams with the correct number of valence electrons, and identify the types of electrons present (i.e. σ, π, lone pair) d. What are the bond angles around both the C atoms and the O atom in (i) and the C atoms in (ii)? (8 points) 13. The formation of NaCl from the elements is a violent EXOthermic reaction. This process may be viewed as the sum of the following steps (a Born-Haber cycle ): sublimation, bond dissociation, first ionization process, first electron affinity, and lattice formation. Create two lists; one for the endothermic processes the other for the exothermic processes. Select one process from each list and describe (perhaps showing the process in reaction format?) what happens. 3
14. (20 points) Fill in the MO energy diagrams for the species listed below. The answer the questions that appear under the MO energy diagram of each species. nitrogen Ν 2 pernitride Ν 2 2 σ 2p σ 2p π 2p π 2p π 2p π 2p π2p π2p π2p π2p σ2p σ 2s σ2s σ*1s σ1s σ2p σ 2s σ2s σ*1s σ1s Show the calculation of the bond order for nitrogen. Show the calculation of the bond order for the above ion. Is nitrogen diamagnetic or paramagnetic? Explain your answer. Is the above ion diamagnetic or paramagnetic? Explain your answer. Draw the Lewis structure of nitrogen. Draw the Lewis structure for the above ion. Does the bond order for nitrogen from the Lewis structure match the bond order from the MO diagram? Does the bond order for the above ion from the Lewis structure match the bond order from the MO diagram? Which should have the longer, weaker bond; nitrogen or the above ion? Explain your choice! 4
BONUS: for up to 10 points (total) For the skeleton structure below: (a) complete the Lewis structure by adding unshared pairs and multiple bonds where appropriate (DO NOT ADD OTHER ATOMS!!) AND (b) specify the hybridization on the atoms labeled a - e: INCLUDE a drawing of the hybridized orbital energy diagram for each atom a - e (filling each the correct number of electrons and identify them as lone pair, sigma bonding, or pi bonding). H O H H O H Ca Cb Oc C Cd Ne H H H H H 5