Pre-Lab #2: Molecular Models
Name __________________________________
1. What do the balls and sticks in the model kit represent?
2. According to today’s lab, what is a valence shell?
3. What do the number of holes in each ball in the model kit represent?
4. What amino acid molecule will you build in today’s lab?
5. What disaccharide will you build in today’s lab?
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Lab #2: Molecular Models
Work in groups of 3-4, each group uses two model kits. Bring your textbook. Refer to pages 23,
34-43.
One of the difficulties of studying molecular bonding is that you cannot see atoms and molecules. It is
difficult to visualize the shape of a molecule based on a two-dimensional drawing in a textbook. In this
lab you will use ball and stick models to construct molecules that are important to living cells.
You will be making covalent bonds by joining various colored “balls” (representing different atoms)
with various “sticks” (representing single, double or triple bonds) that hold the balls together. The
“sticks” represent a pair of valence electrons shared between two atoms. The number of holes in each
ball represents the number of shared electron pairs that the atom normally requires to become stable (i.e.
a full valence shell).
Objectives
1. Build molecules that are biologically important.
2. Compare the amount of rotation around a single, double and triple bond.
3. Perform the chemical reactions of dehydration synthesis and hydrolysis with the molecules that you
and your classmates build.
I. Small Molecules and Monomers
Atoms are usually composed of a nucleus of protons and neutrons with electrons in constant motion
around the nucleus in “electron shells” Each shell can hold a certain number of electrons before the
shell becomes full. Additional electrons then form new shells further away from the nucleus. The
first shell can hold only two electrons. The second and third shells can each hold 8 electrons. A
periodic table arranges atoms in rows by the number of electrons in a particular shell. If the outermost shell in an atom has space for additional electrons, it is called a valence shell. A covalent bond
between two atoms are formed when those atoms share a pair of valence shell electrons.
Materials:
Carbon (C): use black balls with 4 holes
Single bond: white short connector
Hydrogen (H): white balls with 1 hole
Multiple bond: gray longer connector
Oxygen (O): red balls with 2 holes
Nitrogen (N): blue balls with 4 holes (these should have only 3 holes)
Procedure: Build the molecules listed below using the structural formulas provided. Remember single
lines connecting atoms indicate single bonds, double lines indicate a double bond and triple lines
indicate a triple bond. Use the longer gray connectors in your model kit to form double or triple
bonds. Each connector represents one pair of shared valence electrons, so you use two long
connectors to make a double bond and three to make a triple bond.
Build molecules 1-9 using your model kits.
1. Water: H20
2. Ammonia: NH3
3. Oxygen gas: O2
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4. Ethanol: C2H50H
5. Glycine (an amino acid): NH2CH2COOH
Carbohydrate molecules range from small sugar molecules (you will build some below) to large
polysaccharides, which are long polymers of sugar molecules. Simple sugars have molecular formulas
that are some multiple of CH20. For example, glucose and fructose are six-carbon sugars so they have
the formula C6H1206. You can confirm this by counting the numbers of the different atoms in each
molecule.
6. Fructose (fruit sugar): C6H1206
7. Glucose (blood sugar): C6H1206
Without completely taking your fructose molecule apart, rearrange the atoms to make a molecule of
glucose (ask your instructor for help if needed). Your liver does this every time you eat a piece of fruit,
although more efficiently. You may have to take apart some of the smaller molecules to have enough
atoms to make the larger molecules. Save the glucose model to use later in this lab.
II. Chemical Reactions
Chemical reactions occur when atoms within molecules are rearranged to produce new molecules. Build
a second fructose molecule and then combine it with your glucose molecule to make the disaccharide
sucrose. A chemical reaction that combines two molecules into one while producing water is called a
dehydration synthesis.
8. Sucrose C12H22O11 a disaccharide:
1) Build a glucose and fructose model and convert them from linear molecules to rings (see text pg. 37
or instructor for help if needed).
2) Remove the OH (both the oxygen and the hydrogen) from the glucose carbon next to the oxygen
atom in the ring. Remove the hydrogen atom from the fructose OH group where the bond joining
the two molecules will be made.
3) Attach the un-bonded carbon of the glucose to the un-bonded oxygen of the fructose. You now have
a molecule of sucrose.
4) Combine the OH that you removed from the glucose molecule with the H that you removed from
the fructose molecule. You now have a molecule of water.
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9. Glycine+Glycine; a dipeptide:
1) Build a glycine molecule (see previous pages) and remove one H atom from the nitrogen atom.
2) Make a second glycine molecule. Remove an OH from the carbon end of the second glycine
molecule
3) Combine the two amino acids together at the free bonding sites. You now have a dipeptide.
4) Combine your dipeptide with one from another group to form a polypeptide.
10. Make your own organic molecule using at least 5 C atoms, and a combination of as many H, O, and
N atoms as you would like. (Remember to keep it simple and to follow the rules of bonding; C forms
4 bonds, N forms 3, O forms 2 and H forms 1). Record the molecular formula and the structural
formula in your notes.
When you are finished, please be sure that the models have all been returned to the proper kits. Each kit
should contain:
14 carbons (black)
40 linkers
28 hydrogens (white)
8 oxygen (red)
4 nitrogen (blue)
12 multiple bond connectors.
Lab Report
1. Why do Hydrogen atoms form only single bonds with other atoms and not double or triple bonds like
Carbon atoms?
2. What effect do double and triple bonds have on rotation within molecules compared to single bonds?
3. How is it possible to change the shape of your molecular models without breaking any of the covalent
bonds? (Hint: shape depends only on the relative position of atoms in the molecule)
4. If a carbohydrate molecule contained 48 H atoms, how many atoms of C and O will it contain?
(Remember the formula for carbohydrate molecules is CH20)
5. Why is a reaction that links monomers together into a polymer called a dehydration synthesis?
6. What is the molecular formula of the organic molecule that you made? Draw a two-dimensional
model of your molecule.
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