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Class Section:
Lab – Molecular Models
Objective: To demonstrate what functional groups look like and how they react within organic chemicals.
Materials:
5 Black, Carbon Atoms
8 White, Hydrogen Atoms
5 Red, Oxygen Atoms
9 Green, Nitrogen Atoms
22 Bonding Tubes, 2.5 cm
Hydrocarbons: Hydrocarbons are molecules made of just hydrogen and carbon. Carbon
H
has four valence (bonding) electrons and can therefore make four covalent bonds. Hydrogen
has one valence electron and therefore can make only one bond. The simplest hydrocarbon is
methane, CH4, one carbon bonded to four hydrogens. It can also be drawn as to the right.
Use your molecular models to make a methane molecule. The gray connectors represent one
covalent bond, two electrons shared by two atoms. Show your teacher.
H
H
H
C
H
C
H
H
C
H
H
The next more complex hydrocarbon is ethane, C2H6. Use your model set to make an ethane
H molecule.
Next comes propane C3H8 (just like you use in a camp stove!). Use your model set to make a propane molecule.
There are two ways to construct a butane molecule, C4H10. Try to figure out what the two
ways are by experimenting with your model set. Show your teacher when you have figured
out both ways. Now draw both versions of the molecule in your lab notebook showing all
atoms and bonds. Show your teacher the butane molecules you built.
As hydrocarbons get bigger it is difficult to draw in all of the carbons and hydrogens. Because of that scientist
usually use a shorthand way of representing this type of molecule. They just draw in the bonds between carbon atoms
and assume that the hydrogens are in the places they usually are. For example the next more complex hydrocarbon is
pentane, C5H12 and is usually represented by the figure shown below.
Meaning
-C-C-C-C-C-
or
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
Saturated?: Make a model of C2H4, a double bond is required. Show your teacher. You just made what is called
ethene. Draw the molecule in your lab notebook using the abbreviated form (not showing the carbons and
hydrogens). Could you add more hydrogen to the carbons if you wanted to? You could if you did not have the
carbons double bonded together and you would end up with ethane again. C2H4 is a type of molecule called an
“unsaturated” hydrocarbon because it could hold more hydrogen. A good way to remember this is to think of
cleaning up spilled water with a rag. After the rag is saturated it can’t hold any more of the spilled water. Go ahead
and add in the extra hydrogens that can fit with these two carbons. . You have just “hydrogenated” your molecule.
Where have you seen the term “saturated” before? How about “partially hydrogenated”? If you have not heard of
them make sure you talk to someone who has to find out about them.
Alcohols: are hydrocarbons with hydroxyl (OH) groups attached to them. Make a model of the most simple,
methanol, CH3OH. Oxygens are red spheres. Make ethanol, C2H5OH the kind of alcohol that people drink. Make two
models of propanol, C3H7OH that are different from each other and show them to your teacher. Now draw
structural formulas of the two types of alcohol in your notebook. The one with the hydroxyl group on the middle
carbon is called isopropyl alcohol, or commonly “rubbing” alcohol.
H
H
O
C
H
C
Carboxylic Acids: Sometimes organic (made of carbon, hydrogen and oxygen)
OH
compounds can be acidic or basic. Carboxylic acids can easily lose a hydrogen ion when
dissolved in water. Remember the definition of an acid? Make ethanoic acid,
CH3COOH, the simplest carboxylic acid and show it to your teacher.
Amino Acids: these are organic compounds that have a carboxyl group (COOH) and an amine group (NH2)
attached to them.
H
H
O
\
//
N -- C -- C
/
\
H
R
OH
The above diagram is the generalized structure of an amino acid. Amino Acids get hooked together to form
proteins. Make Alanine, NH2CHCOOHCH3, one of the simple amino acids. Make one part at a time and assemble
them into the whole (first the NH2(Use the 3 hole Nitrogen), then the “central” CH, then the COOH, then the CH3,
and then put them together in the only way possible). Show your teacher the alanine. Draw your molecule in your
lab notebook. Now make another Alanine.
Amino acids can join together by making what is called a “peptide bond”. Remove the OH from the carboxyl group
(COOH) of one amino acid and one of the Hs from the amine group (NH2) of the other. Put the OH and the H
together to form a water molecule and hook the N to the C with a new bond. Show your teacher when you have this
finished creating your “dipeptide”. When you have three or more amino acids hooked together it is called a
“polypeptide” or a “protein”. One of the smallest proteins in the human body is insulin, which is made of 54 amino
acids hooked together by peptide bonds. Notice the pattern of the “backbone” of this “protein”. What is the pattern
you observed? _________________________________
Carbohydrates: These are ring shaped molecules most of which have the formula C6H12O6.
Make two Glucose molecules (there aren’t enough so, table 1 work with 2, 3 with 4, etc…).
Each of these individual ring molecules is known as a “monosaccharide” or simple sugar.
Now hook your Glucose molecules together by removing an OH
group from one and an H from the other as shown in the figure to
the right. Put together the OH and H to form a water molecule.
This is called dehydration synthesis. After you have connected
your Glucose molecules together you have made a “disaccharide”
(or sugar) called maltose (like in a chocolate “malt”). Show your teacher.
Polysaccharides like starch are just a whole bunch of
monosaccharides hooked together. How do you
think we digest these large substances?
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