Name. CHM 115 EXAM #2 Practice KEY. a. N Cl b. N F c. F F d. I I e. N Br. a. K b. Be c. O d. Al e. S

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1 Name CHM 115 EXAM #2 Practice KEY 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. ALL OF THESE have TEN valence electrons [:C N:] - :C O: [:N O:] The triple bond between the C and O should be the shortest and strongest. In addition to being a triple bond, the -1 and +1 formal charges indicate that a strong partial ionic character will exist in this bond (adding to the strength of the bond).

2 (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 BrF 5 Draw the BEST Lewis structure of this interhalogen molecule and show formal charge calculations for each type of atom FC (X) = valence bonds lone pair e- FC (Br) = = 0 All F: FC (F) = = 0 Give the names of (a) the electron pair geometry and (b) the molecular shape, (a) otahedral (b) square based pyramid (or square pyramid) Specify the hybridization of the Br AND draw the energy diagram for the hybridized orbital (you know - the boxes with electrons in them). l.p. σ σ hybridization is sp 3 d 2 Fluorine electrons are shown in red, l.p. stands for lone pair, and σ is a sigma bond. Is this species polar or nonpolar? Explain. Polar because the five bond dipoles do not cancel. (b) In the spaces provided, do the following for BrF 3 Draw the BEST Lewis structure of this interhalogen molecule and show formal charge calculations for each type of atom FC (X) = valence bonds lone pair e- FC (Br) = = 0 All F: FC (F) = = 0 Give the names of (a) the electron pair geometry and (b) the molecular shape, (a) trigonal bipyramidal (b) T-shaped Specify the hybridization of the Br AND draw the energy diagram for the hybridized orbital (you know - the boxes with electrons in them). l.p. l.p. hybridization is sp 3 d Fluorine electrons are shown in red, l.p. stands for lone pair, and σ is a sigma bond. Is this species polar or nonpolar? Explain. Polar because the three bond dipoles do not cancel. 2

3 (22 points) 12. For the following two species complete the tasks specified below in a - d. i. CH3COOH ii. C 2 H 4 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 in CH 3 sp 3 C in CO sp 2 O between CO and H sp 3 C in CH 2 sp 2 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) C in CH 3 σ C in CO π C in CH 2 For both C π O between CO and H lp lp σ σ d. What are the bond angles around both the C atoms and the O atom in (i) and the C atoms in (ii)? C in CH 3 ~109.5 C in CO ~120 O between CO and H ~109.5 C in CH (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. ENDOthermic (energy needed) Sublimation of sodium metal (solid to gas) Na(s) Na(g) Bond dissociation of Cl2 (breaking bonds) ½ Cl 2 (g) Cl(g) 1 st IE for sodium (remove one electron) Na(g) Na + (g) EXOthermic (energy released) 1 st EA for chlorine (one electron gained) Cl(g) Cl - (g) Lattice energy (gas ions combine to form solid) Na + (g) + Cl - (g) NaCL (s) 3

4 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 10 valence, 2 2 pernitride Ν 12 valence, 14 total e total e - σ 2p σ 2p π 2p π 2p π 2p π 2p π2p π2p π2p π2p σ2p σ 2s σ2p σ 2s σ2s σ2s σ 1s σ 1s σ1s σ1s Show the calculation of the bond order for nitrogen. BO = ½ (bonding antibonding) BO = ½ (10-4) = 3 Is nitrogen diamagnetic or paramagnetic? Explain your answer. Molecular nitrogen, N 2, is diamagnetic because it possesses no unpaired electrons (all electrons are paired). Draw the Lewis structure of nitrogen. Does the bond order for nitrogen from the Lewis structure match the bond order from the MO diagram? Yes it does! Show the calculation of the bond order for the above ion. BO = ½ (bonding antibonding) BO = ½ (10-6) = 2 Is the above ion diamagnetic or paramagnetic? Explain your answer. The pernitride ion, N 2-2, is paramagnetic because it possesses unpaired electrons. Draw the Lewis structure for the above ion..... [:N=N:] -1-1 Does the bond order for the above ion from the Lewis structure match the bond order from the MO diagram? Yes it does! (BUT; the Lewis structure does not predict the paramagnetism ) Which should have the longer, weaker bond; nitrogen or the above ion? Explain your choice! The pernitride ion definitely should have the longer and weaker bond. The bond is only a double bond (vs. a triple bond in N 2 ) AND the negative formal charge (-1) on each N atom would repel one another. 4

5 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 (a) sp 3 the four C electrons (only) are shown σ (b) sp 3 the four C electrons (only) are shown σ (c) sp 3 the six O electrons (only) are shown lp lp σ σ p (d) sp 2 π the four C electrons (only) are shown (e) sp 3 the five N electrons (only) are shown lp 5

CHM 115 EXAM #2 Practice

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