2045C   Exam #3 (chapters 7 & 8)
     1. Use Rydberg equation to:   (12)
         (a) Determine energy levels for electron emitting radiation of approximately 1940nm.
         (b) Perform calculations to show electron returning from 7® 4 emits longer wavelength than
              than electron returning from 6® 2.
        (c) An electron elevated from 2® 6. Calculate the longest wavelength possible in the process
             of returning to original energy level.
        (d) If an electron returns to the third shell, is it possible to emit red light (about 700nm)?
              Answer with calculations!

     2. For electron in 4f subshell, distance between ends of standing wave is 3.0 nm.   (8)
         (a) Draw the standing wave including nodes (use circles).
         (b) What is the wavelength associated with this wave?
         (c) How many regions of electron density?
         (d) Provide values for all orientations.

     3. Represent specified electrons using arrows/boxes:  (16)
          (a) N = 1,2   L = 1,2   ML = +1,+2       (b) N = 4    L = 2,3   ML = -1 to +1    MS = + ½
          (c) For Kr(#36):  L = 1  ML = 0          (d) For Rn(#86):  ML = +2

     4.  Which atom or ion in each of the following pairs would you expect to be larger?  Explain!  (8)
          (a) Cu+1/Cu+2    (b) Na+1/F-1       (c) Cl-1/Br-1   (d) Mg/S

     5.  (a) Calculate energy in joules for one photon with wavelength of 480nm.   (9)
          (b) State which of the following are paramagnetic:  Ca  Sc  Cr  Zn  Kr
          (c) Calculate effective nuclear charge for sulfur (S).

     6. Provide resonance forms for each of the following:    (12)
         (a) HCO2-1      (b) NO2-1      (c) O3

     7. Draw Lewis structures:   (15)
          (a) BHF2    (b) SeF4      (c) SiF4      (d) GeF2     (e) SF6

     8. (a) CaO vs MgO:  Which compound has the greater lattice energy? Explain!     (15)
         (b) Assign formal charge to each atom for
        (c) Draw isomers for C3H6Cl2
        (d) Using bond orders, explain why S-O bond length longer in SO3 than in SO2.
      (e) Provide electron configuration for Mn+3 and for Ce+3.
 

     Answers
      1. (a)  91.1/l = 91.1/1940 = 0.0470     1/42 - 1/82 = 0.0469   8®4
           (b)  7®4 l =91.1/(1/42 - 1/72) = 91.1/0.0425 = 2140nm
                 6®2 l =91.1/(1/22 - 1/62) = 91.1/0.222  = 410nm
           (c)  6®5 l =91.1/(1/52 - 1/62) = 91.1/0.0122  = 7450nm
           (d)  91.1/700 = 0.130 = 1/32 - 1/n2 = (0.111 - 1/n2)  Impossible


      4. (a) Cu+1   same number protons but 1 more electron
          (b) F-1     same number electrons but fewer protons
           (c) Br-1   filled s&p subshells further out (4th shell)
           (d) Mg    atomic size decreases left to right

     5.  (a) n = c/l = (3.0x108 m)/4.80x10-7 m) = 6.3x1014 s-1
                   E = hn = (6.63x10-34 J s)(6.3x1014 s-1) = 4.2x10-21 J
          (b)  Sc  Cr
          (c) Effective nuclear charge for S = +16 (protons) - 10 (core electrons) = +6


     8.  (a) MgO:  same charges but Mg+2 smaller than Ca+2

       (d)  SO2:  Bond Order = 1.50        SO3: Bond Order = 1.33
             Bond length increases with decreasing bond order.

      (e)    Mn+3  [Ar] 3d4
              Ce+3      [Xe] 4f1