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Chemistry 221
Take-home Quiz #3 (20 points ……………………..)
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.
Droplet
A
B
C
D
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 waveparticle duality of light?
b) What evidence do scientists have that light
behaves like a particle? Like a wave? Briefly
explain.