9/30/2014
ALEKS Alex H. Yuan - 09/30/2014 11:34:40 PM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
Alex H. Yuan - 09/30/2014 11:34:40 PM EDT
General Chemistry (First Semester) / Chem 110 FA 2014 – CH110 FA14 S25-36 (Dr.
Barber)
1.
Drawing Lewis structures for simple organic compounds
Draw the Lewis structure for chloroethane
Be certain you include any lone
pairs.
It can be challenging to draw the Lewis structure of an organic compound, because organic
molecules usually don't have a single central atom that you can use as a starting point.
What organic molecules usually do have, however, is an inner skeleton made mostly of
carbon atoms bonded to each other, covered by an outer skin made mostly of hydrogen
atoms bonded to the carbon skeleton atoms. Those facts suggest the following general
plan for drawing the Lewis structure of organic compounds:
1. Draw a skeleton using just the carbon atoms.
For example, the
molecule has two carbon atoms, so you can begin
by drawing this skeleton:
C
C
It's reasonable to start off assuming the carbon atoms form only single bonds to
each other. But you may need to change some of the single bonds to double or
triple bonds later on.
2. Add any heteroatoms to the skeleton.
Heteroatoms are atoms of elements other than carbon and hydrogen. Some of
the most common heteroatoms are atoms of a halogen, oxygen, or nitrogen.
Halogens. Halogen atoms in organic molecules typically form only one chemical
bond to the central skeleton, like hydrogen atoms. You can actually think of
them as forming part of the skin of a molecule.
https://secure.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lJiYsPgPQIfQokR4hWMNIe-wKsFh3XosS7WHcmXKZd4GiLU3qxlZmco8pYUac1kKlp…
1/3
9/30/2014
ALEKS Alex H. Yuan - 09/30/2014 11:34:40 PM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
For example, the
molecule has one halogen atom. It's
reasonable to join it to the skeleton like this:
C
C
Cl
Don't forget the three lone pairs that must be around the halogen atom to
satisfy the octet rule.
Oxygen. Oxygen forms two chemical bonds, so it can be embedded in the
central skeleton. However, oxygen atoms most often appear in organic
molecules as part of hydroxy groups, forming a single bond to a carbon
skeleton atom, or as part of carbonyl groups, forming a double bond to a carbon
skeleton atom.
Nitrogen. Since nitrogen can form three chemical bonds, it's even more likely
than oxygen to be embedded in the central skeleton. However, in many
common organic molecules nitrogen atoms appear as part of an amino group,
forming a single bond to a carbon skeleton atom.
3. Add the hydrogen skin.
It's at this point that you might need to change your mind about the bonding in
the skeleton. If you find that you don't have enough hydrogens left to cap each
dangling chemical bond, then you'll need to change some of the single bonds in
the skeleton into double or triple bonds.
For example, in the case of
it turns out there are just the right
number of hydrogen atoms left to cap each dangling bond in the skeleton
drawn in Steps 1 and 2 above.
H
H
H
C
C
H
H
Cl
Note: When you count the hydrogens available for capping the remaining dangling bonds,
don't forget that you may have used some hydrogens up by adding hydroxy or amino
groups in Step 2.
https://secure.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lJiYsPgPQIfQokR4hWMNIe-wKsFh3XosS7WHcmXKZd4GiLU3qxlZmco8pYUac1kKlp…
2/3
9/30/2014
ALEKS Alex H. Yuan - 09/30/2014 11:34:40 PM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
H
H
H
C
C
H
H
Cl
Copyright © 2014 UC Regents and ALEKS Corporation
https://secure.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lJiYsPgPQIfQokR4hWMNIe-wKsFh3XosS7WHcmXKZd4GiLU3qxlZmco8pYUac1kKlp…
3/3