Chemistry 221

Take-home Quiz #3 (20 points due October 27, 2004)

Backes/PCC Rock Creek                                                                        Name                                                                     

1.  Two compounds have formulas A2B6 and CD3.  One of these compounds is an ionic compound and one a molecular one. 

How can you tell from the formulas which one is ionic? 

a)  For the ionic compound, if the negative ion has a 1 charge, what is the charge of the positive ion? 

b) Suggest two ions that might form this compound and draw a microscopic sketch of several formula units of this compound. 

c) How would a sketch representing the molecular compound differ from the one for the ionic compound? 








2.  Briefly summarize (in a few sentences) the evidence used by J.J. Thomson to argue that cathode rays consist of negatively charged particles.  









3.  Millikan determined the charge on the electron by studying the static charges on oil drops falling in an electric field.  A student carried out this experiment using several oil drops for her measurements and calculated the charges on the drops.  She obtained these data. 





Calculated Charge (C)


1.60 x 10-19

3.15 x 10-19

4.81 x 10-19

6.31 x 10-19

What is the significance of the fact that the droplets carried different charges?  What conclusion can the student draw from these

data regarding the charge of the electron?  What value (and to how many significant figures) should she report for the electronic charge? 









4.  a) Explain what is meant by the wave-particle duality of light?






b) What evidence do scientists have that light behaves like a particle?  Like a wave?  Briefly explain.