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Unformatted text preview: s set number two, and the molecule's parent structure and shape are both linear. We
also see that the carbon-oxygen is polar (quite polar) with the oxygen being more
electronegative. But, since the molecule is symmetrical, the two dipoles on each side of the
molecule are exactly identical, and therefore cancel one another out: One way to think of this is if two children of exactly identical strength were pulling a wagon. If
they were pulling in exact opposite directions, the wagon is not moving anywhere; it's stuck.
However, if they were not equally strong, or if they were pulling in kind of similar direction,
then the wagon would move, maybe not towards one of the children exactly, but it would move.
As a result, carbon dioxide is non-polar because it is a highly symmetrical molecule.
To see why something that is, say, square planar might be non-polar, we have to consider
what it would look like. An example of such a shape might be something like [Cu(NH4 )4 ]+2 ,
which is square planar. Anyway, consider the following diagram: As you can see, if the molecules on diametrically opposed corners are identical, any dipole
present would cancel out exactly.
This has been kind of vague, but all the information you need is contained within this
document. Any questions, comments or suggestions should be sent to me by email, phone, or by
stopping by in a friendly little visit WITH NO VIOLINS!
Dakota State University Page 110 of 232 Experiment 9: VSEPR General Chemistry I and II Lab Manual It seems to me that the best way to learn Lewis Dot Structures is to practice with them.
Fortunately we ha ve an entire class of compounds that are particularly well suited for such
practice, a class so large, in fact, that it is often given a year of study in most Universities. It’s
called organic chemistry.
Yep, organic chemistry. I know what you are thinking, “mmmm...chocolate”. But you are
ready for this challenge. Below you will find a series of empirical formulas. For each
formula, find an allowed Lewis Dot structure, noting special instructions where given. Some
of these formulas exist in “isomeric” forms, that is, there is more than one possible Lewis
Dot Structure. In these cases, try to find as many possible structures as indicated. For each
valid Lewis Dot Structure, determine the molecular shape using VSEPR, and determine if it
is polar or not. Do this part of the experiment before the computer part!
Let’s get started! Take notes in your lab notebook, as if this is a normal experiment.
Formula 1: CH4 Formula 2: CH2 O Formula 3: CH4 O Dakota State University Page 111 of 232 Experiment 9: VSEPR General Chemistry I and II Lab Manual Formula 4: C2 H6 Formula 5: C2 H4 Formula 6: C2 H2 Formula 7: C2 H6 O (2 isomers; hint: for one isomer, try placing the oxygen between the carbons
for ONE of the isomers) Formula 8: C2 H4 O (2 isomers)
Dakota State University Page 112 of 232 Experiment 9: VSEPR General Chemistry I and II Lab Manual Formula 9: C2 H7 N Formula 10: C2 H4 O2 (at lea...
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