Name(s): ___________________
Section: __________
ORGANIC MOLECULES (1) WORKSHEET
Bonds, Formulas, Structures, & Shapes
Review the fundamental principles of covalent bonding, Lewis structures, and VSEPR. These concepts are
absolutely indespensible to the understanding of organic chemistry. Practice and master them. They will be used
repeatedly throughout the course and are absolutely essential to your understanding and success.
1. The word "bond" in Webster's Dictionary has twelve different meanings as a noun and six as a verb. Define in
your own words in one short sentence what you think “bond” means in the context of organic chemistry.
2. Write molecular formulas for as many different possible molecules that can be produced from combinations of
the following elements (Provide as many as you think reasonable. If there are too many to consider, provide a
number that you think might approximate the total, eg. hundreds, thousands, millions, etc.) For example: Na and
Cl has only one compound, NaCl, but there are several for Na, Cl plus O, one possibility is sodium chlorite,
NaClO2.
Sodium and Chlorine: NaCl, sodium chloride, has only this one possibility.
a) Na and Cl and Oxygen (NaxClyOz): (consider four possibilities)
b) Sodium and Carbon and Oxygen (NaxCyOz): (consider all possibilities that are reasonable & accurate)
c) Carbon and Hydrogen and Oxygen (CxHyOz): (consider all possibilities)
d) What theoretically can account for the different possible number of molecules in the above 3 cases?
(Briefly answer in a sentence or two.)
3. Complete the Lewis structures for the following compounds showing all electrons:
The forces that bind atoms can vary considerably and can be related to the differences in the electronegativities of
the atoms. Very large differences relate to very strong bonds between the atoms, which are ionic bonds. For cesium
flouride, CsF, which has a bond that is among the highest in ionic character the difference is 3.2: 4.1 (e.n. F) minus
0.9 (e.n. Cs). In diatomic molecules such as chlorine, the difference is zero. The atoms are molecularly bound, but
there is no ionic character. The bond is purely covalent, i.e. where the electrons are shared equally by both atoms.
Ionic character is represented by the more electronegative atom having a stronger share of the bonding electrons.
The scale from 3.2 to 0 is one of relative bond strength with a spectrum of different shades of bonding character
across it. Bonds more typically range somewhere along the scale and are not at one of the extremes.
In organic molecules, the bonds will be for the most part covalent, but they will not be purely covalent like diatomic
chlorine. They will have small differences. These differences polarize the bond and can be represented by a partial
positive charge (δ+ ) for the less electronegative atom and a partial negative charge (δ-) for the more electronegative.
In general chemistry, you were asked to determine whether simple, covalently bonded molecules such as HCl were
polar or non-polar. This question is very important in complicated organic molecules, but it is more difficult to
answer since the overall polarity of the molecule will be determined by sum of all of the polar bond effects in 3dimensions. Electronic and molecular structure (VSEPR), individual bond polarities, and their net effect must all be
considered.
Complete the table on the next page which relates Lewis structures to 3-dimensional electronic and molecular shape,
and the polarity of a molecule.
http://chemconnections.org/COT/organic1/VSEPR/
4. Refer to the above Webpage. Click on the active link in each of the squares in the Webpage for a molecule's
image. The images must be manipulated in order to get an accurate view of the molecules; not all of the atoms
will be visible without doing so. Complete the following table for each image: 1) Write the molecular formula
for the molecule. 2) Identify the number of valence electrons for each atom in the molecule and the total number
of electrons for the complete molecule. 3) Draw a Lewis structure that represents the molecule. 4) Identify the
molecular shape of the molecule. 5) Consider the bond polarities, and note if the overall molecule is polar or
non-polar. For example, 4A: SO2, S=6, O=6, SO2=18, bent, polar
A
B
C
1
2
3
SO2, S=6, O=6,
SO2=18; bent, polar
4
5. Define in your own words what you think “resonance” means in the context of bonding, and if all structures can
have “resonance”?
6. In each of the following structures clearly indicate any and all atoms that have a formal charge by drawing the
respective charge (+) or (-) above the atom.
..
CH3
H3C
: O:
N
CH
CH3 3
H3C
N
..
CH3
H O:
::
CH3
..
N
H3 C : :
CH3
: O:
..
O:
::
H3 C
..
: O:
CH3
H3C
C:
H3C
CH3
H3C O H
H O H
::
CH3
:O
..
H3 C O :
..
C
..
H
H3C
H3C
CH3
CH 3
: O:
CH3
CH3
::
CH2
H3 C
H
CH3
CH2
Refer once again to: http://chemconnections.org/COT/organic1/VSEPR/
Using the jmol bond length feature, check the respective bond lengths for 4A, SO2, by double clicking on the sulfur
atom and then each respective oxygen atom. In the Web model, the bond lengths are equal (1.565 Angstroms,
0.1565 nm) for both sulfur to oxygen bonds, despite a Lewis structure which shows an S-O single bond that is >1.57
Angstroms (Å), and an S=O double bond that is < 1.57 Angstroms (Å).
The two possible structures for SO2. are shown below. In one case there is a single bond on the right of the sulfur
atom, double on the left and in the other a double bond on the right and a single bond on the left.
..
..
O S O:
.. .. ..
..
..
: O S O
.. .. ..
The actual net result is a weighted average of the two. In this case, the Sulfur-Oxygen bond is a double bond about
50% of the time and a single bond about 50% of the time.
7. Draw 3 different Lewis structures for the polyatomic carbonate ion CO32- below using arrows to show the
-
electron movements between the three structures. (The 2 charge indicates that there are 2 additional electrons in
the ion.) Check the bond lengths with jmol and record the bond length values in Angstroms (Å) for the
respective bonds. Repeat the steps for the acetate ion.
Carbonate:
C-O #1 length =
C-O #2 length =
C-O #3 length =
Acetate:
C-O #1 length =
C-O #2 length =
8. Consider that a pure C-O single bond is about 1.40 Å, and a pure C=O double bond is about 1.20 Å. Briefly
describe the bond character (bond order) of the Cabon-Oxygen bonds in the respective polyatomic ions.
9. Draw Lewis structures for methanol, diethyl ether, formaldehyde, acetone, and acetic acid.
methanol:
diethyl ether:
formaldehyde:
acetone:
acetic acid: