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1 Page 1 Practice for Exam 4. Note: Many if not most of the questions below appeared on a past exam, but not necessarily on the same exam. I've also combined problems from at least two past exams onto this exam, so that is why the numbering is all crazy. I have not taken pains to make sure all topics are equally represented on this practice exam (NTE: TERE ARE N PRBLEMS CRRESPNDING T PS12 MATERIAL SRRY!), so as usual, remember to use your problem sets, worksheets, and VSEPR lab as the ultimate guide as to what topics and problem types are fair game on the exam you will actually take. The following information (and maybe other things) will be provided on the first page of the exam: Possibly Useful Information (NTE: Some of these geometry names are "fake" (made up by me and not used by chemistry for anything; you need to be familiar enough with the names to pick them out from the list you will be given): triangular (trigonal) pyramidal square bipyramidal linear triangular (trigonal) Tshaped square planar triangular (trigonal) planar seesaw tetrahedral angular (bent) (Vshaped) octahedral trigonal bipyramidal square pyramidal trigonal pyramidal 1B. Circle the correct answer (18 pts total) (2 points each) 2 (a) The formal charge on the S in sulfate (see right) is: S i) 2 ii) 1 iii) 0 iv) +1 v) +2 (c) The first ionization energy is predicted to be i) greater for Br than. ii) greater for Br than Br +. iii) greater for Br than Se. (primarily) because the outer electrons i) are closer to the nucleus in Br than in the other atom or ion. ii) see a greater positive charge from the nucleus in Br than in the other atom or ion. iii) are held less tightly in Br than in the other atom or ion. (d) Which statement is true: i) CD is the weaker bond. ii) AB is the shorter bond iii) both i) and ii) Potential Energy 0 AB CD Distance Between Atoms

2 Page 2 The following 6 questions were not on any exam I created them for practice in 07 (some of the reasoning choices are not the best exam questions [and none represent a complete explanation], but I threw them in anyway). Remember, you must look at the problem sets and worksheets to properly prepare for the exam a lot of things are new in 07 and I do not have time to write problems that correspond to ALL the topics that are fair game on the exam. These few problems were constructed directly from problem set questions or worksheet questions. Can you find them? Use EAC problem set problem to prepare for possible questions. (e) Which species has the most negative electron affinity? i) ii) + iii) 2+ iv) i) The more negative the electron affinity, the less favorable a process is. ii) It is more favorable to add an electron to than the other species. iii) is more negative than the other species. iv) The more positive an ion, the stronger the force of attraction for added electrons. (e) Which species is likely to be the least likely to exist in nature for any length of time (i.e. is the least stable)? i) As 4 ii) P 4 iii) N 4 iv) Sb 4 i) second row elements cannot stably have more than 8 electrons around it ii) the larger the central atom, the stronger the bonding and more stable the species iii) the smaller the electronegativity, the weaker the bonding iv) all of the above v) none of the above (e) Which species is the most stable with respect to pulling an electron away from it? i) K + ii) Ar iii) Cl iv) all are equal in this regard i) noble gas atom are fundamentally the most stable ii) this species has the greatest Z eff iii) all species have a filled shell iv) the farther to the right in the periodic table, the greater the ionization energy

3 Page 3 2B. Write T (True) or (alse) for the following statements. If the statement is false correct it by changing, dropping, or adding a few words (6 points) a) Polarity is a number that reflects the tendency of an atom to pull bonding electrons to itself. b) Mg 2+ is the common ion formed by Mg because the third ionization energy of Mg is extremely large. ree Response QuestionsB 3B. (6 pts) Are these two Lewis structures considered equally good representations for NC? If not, which is better? Give your reasoning. N C N C 4B. (16 pts) Draw Lewis structures for each of the following (include equivalent resonance structures, if applicable: (a) Cl 2 (b) As 4 (c) N 3 5B (added in 07 for practice): State the ECG and CG of each of the species in problem 3B and 4B above, and state the hybrid orbitals used by the central atom in each. Also

4 Page 4 state the approximate bond angles in each (only one center in each, so all angles are the same). 11B. (5 pts) If the following drawings are meant to very simplistically represent the distribution of electrons in two different atoms, predict which atom would have the greater ionization energy, and provide your reasoning e 8 e 8 e 1 e Atom A 2 e 8 e 8 e Atom B 12B. (3 pts) Consider C 2, whose structural formula is: C (a) Draw arrow symbol(s) on the Lewis dot structure to properly indicate all bond dipoles (i.e., all polar bonds) in the molecule. (b) Which atom will have the greatest partial negative charge? (a) C (b) (c) 13B. Variation of problem (look closely at which centers were chosen!) from the VSEPR lab (and make sure to look at PS11 and the rest of the VSEPR lab, the material of which is not represented much on this practice exam). Be sure to add lone pairs, as needed, to this structure!

5 Page 5 C 5 CG(N): NC 3 angle: C 4 Cl CG(C 1 ): CG(C 3 ): C 1 C 2 angle: N C 3 NC 3 angle: C 2 C 1 CG(C 5 ): C 5 C 4 angle: (a) State the total number of sigma bonds and pi bonds in this molecule. : : (b) State the hybrid orbitals used by each of the four centers identified above to make sigma bonds: CG(N): CG(C 1 ): CG(C 3 ): CG(C 5 ): (c) State the orbitals used for pi bonding for the centers that involve pi bonds. I M SRRY, BUT TERE ARE N PRACTICE EXAM PRBLEMS AVAILABLE R PS12 MATERIAL. AGAIN, PLEASE LK AT TE PRBLEM SET 12 ANSWER KEY AND PRBLEMS.