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Chemistry test - CHEM 107 100-Point Test Name Section 01...

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Unformatted text preview: CHEM 107 100-Point Test Name Section 01 Chapters 7 & 8 Friday, April 04, 2008 Instructions: Answer question 3 by filiing in the blanks. Answer the other questions on separate pages. A second copy of this test was provided for you to re-work as a take-home assignment (due prior to class on Monday, April 07) for possible bonus points. 1. (48 pts, 12 pts each) For each of the following species, write the Lewis dot—structure, attempting to satisfy the octet rule if possible. If resonance occurs, draw all resonance structures. Determine the formal charge and oxidation number of each atom in each species. ' (2.) (N03) ‘ ab.) (P093 ‘ («2) Ken (d.) (CN)" 2. (12 pts) For any of the species in question 2 having a central element capable of an expanded octet (from coordination number 4 to 5 and 6) and with external elements capable of forming multiple bonds, write possible expanded dot-structures and comment on whether they contribute much to the stability of the species. 3. (26 pts, 2 pts each) Enter the letter (A or B) of the correct response in the blank provided. (a) Which has the bigger atomic radius, (A) K or (B) Kr? (b) Which has the lower first ionization energy, (A) K or (B) Cs? (c) Which has the lower second ionization energy, (A) K or (B) Ca? (d) Which has the higher electron affinity, (A) C1 or (B) Br? (e) Which is larger, (A) KJr or (B) Cl”? (f) Which is a representative element, (A) Sc or (B) S? (g) Which bond is more ionic, (A) NaCi or 0}) KCl? (h) Which bond is more covalent, (A) NaCl or (B) NaBr? (i) Which species is isoelectronic with C02, (A) (N02)_ or (B) (OF2)2+? (j) How many valence electrons are in OFZ, (A) 20 or (B) 26? (It) How many eiectrons are in OF;, (A) 20 or (B) 26? (I) How many bonding electrons are in 0132, (A) 4 or (B) 6? (In) How many non-bonding electron pairs are in OFg, (A) 8 or 03) 2? i||||l|l|HH 4. (4 pts) According to general trends in the periodic table, the order of ionization energies (IE) should be IEN < IE0 < IEF. Experimental measurements indicate that IE0 < IEN < 1131:. On the basis of electron configurations, explain the observed order, 5. (10 pts) The molar enthalpy of formation of water vapor, AHfO(H20(gas)), = — 242 kJ/Inol. Average bond enthalpies in kJ/mol are as follows: BH(H2), 43%;. BH(02), 495; BH(O—H), 463. (a) Use Hess’s Law of Heats of Formation to determine the value of fifor the reaction, C . 2 H20(gas) -—> 2 PIKE”) + 02(33-5) ‘ {j (b) Use Hess’s Law of Bond Enthalpies to estimate AH for the same reacu'mn. (c) Calculate the percent error caused by use of bond enthalpies in estimating AH for this reaction. ...
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