Lab # ______: Building Molecules
Date ________
In this exercise you will be using “ball and stick” kits to make models of various molecules.
You will use wooden balls drilled with holes to represent atoms and sticks or springs to represent
chemical bonds. A chemical bond is energy that can hold 2 atoms together. The molecules you will
build in this exercise are held together by covalent bonds. This means that the atoms are held together
because they are sharing electrons.
In biology we are concerned primarily with four kinds of atoms:
1. Carbon (represented by a black ball) can bond to 4 other atoms. Choose a black ball and
insert 4 sticks into its holes (Note that he black ball has only 4 holes)
2. Nitrogen (represented by a blue ball) usually bonds to 3 other atoms in biological molecules. .
Choose a blue ball and insert sticks into 3 of the holes in the ball.
3. Oxygen (represented by a red ball) usually bonds to 2 other atoms in biological molecules.
Choose a red ball and insert 2 sticks into it. (Note that the red balls have only 2 holes)
4. Hydrogen (represented by a yellow) can bond to 1 other atom. Choose a yellow ball and
insert a stick into it. (Note that the yellow balls have only 1 hole)
When atoms are held together by chemical bonds they make molecules (for example, the same
stick that comes from a carbon also goes into a hydrogen, thus holding the two atoms together). If a
molecule is made of only one type of atom, it is called an element. If a molecule is made up of two
or more different kinds of atoms it is called a compound.
Use balls and sticks to build the following molecules. Remember, you have 4 sticks (bonds) coming
out of a carbon atom, 3 sticks (bonds) coming from a nitrogen atom, 2 sticks (bonds) coming from an
oxygen atom, and 1 stick (bond) coming from a hydrogen atom. Draw a structural formula for each
after you build it.
MOLECULAR FORMULA
NH3
(ammonia)
H2O
(water)
CH4
(methane)
H2
(hydrogen)
CH4O
(methyl alcohol)
STRUCTURAL FORMULA
ELEMENT OR
COMPOUND?
Sometimes atoms form 2 bonds to the same atom. This is called a double bond. To represent a
double bond you will need to use something more flexible. You will use the springs included in the
kits for these double bonds. Triple bonds (3 bonds between the same two atoms) are done the same
way. Using springs to represent double and triple bonds, build these molecules:
MOLECULAR FORMULA
O2
(oxygen)
CO2
(carbon dioxide)
C2H4
(ethene)
N2
(nitrogen)
C2H4O2
(acetic acid – the acid found
in vinegar)
HINT: Acetic acid is often
written as CH3COOH
STRUCTURAL FORMULA
ELEMENT OR
COMPOUND?
Sometimes molecules rearrange their chemical bonds with another molecule to form different
molecules. For example, O2 and combine with 2 H2 molecules to form 2 H2O molecules:
2 H2
+
O2
REACTANTS
2 H2O
PRODUCTS
The molecules on the left (the ones you start with) are called reactants. The molecules on the right
(the ones that are made) are called the products. The change from reactants to products is called a
chemical reaction.
Build the reactants below. Once you have built them try to rearrange the bonds to make the products
shown. Remember that you can only use atoms from the reactants to form the products.
REACTANTS
#1:
#2:
N2 + H2
(as many of each as you need
to build the products)
CO2 + H2
(as many of each as you need
to build the products)
PRODUCTS
NH3
CH4 + O2
A. Write a balanced equation for each chemical reaction. Label the reactants and the products in
each.
#1:
#2:
B. Explain the difference between H2 and 2H.