CHEMISTRY EXPERIMENTS ON FILETM
EXPLORING PATTERNS IN CHEMISTRY • 4.08–1
What Makes A Good Conductor?
Topic
Chemical bonding
Introduction
An electrical current is the free movement of electrons. If a material allows the
passage of electrons through it, it is a conductor. The way in which the atoms are
combined within the material (its bond type) determines whether or not the
material will allow the flow of electrons.
Elements classified as metals lose electrons easily. The electrons in a metallic
element are free to move along all the atoms in the metal, and these materials are
good electrical conductors. The atoms are held together by attractive forces
between the nuclei and these freely moving electrons. These substances are said
to have metallic bonds. Elements classified as non-metals and compounds
composed of non-metallic elements are held together by covalent bonds. Atoms
in these substances share one or more specific pairs of electrons. Their electrons
are localized (they cannot move freely throughout the substance), and these
materials do not therefore conduct electricity. A few elements exhibit the
properties of both metals and non-metals. They are called semi-metals or
metalloids.
When a metal and non-metal element combine to form a compound, a different
type of bonding takes place. Atoms of the metal lose electrons and atoms of the
non-metal gain electrons, forming charged particles called ions. The metals form
positive ions and the non-metals form negative ions. The oppositely charged ions
in the compound attract each other. This is called ionic bonding. Although the
compound is made up of charged particles, the numbers of negative and positive
particles are always equal and the compound is electrically neutral. In its solid
form, the substance’s charged particles are not free to move around, so solid
ionic compounds do not conduct electricity. However, when these compounds
are melted or dissolved in water, the charged particles (ions) are separated and
free to move about. We say they are dissociated. In solution these compounds are
electrical conductors. Substances that conduct electricity in solution are called
electrolytes and those that do not are called non-electrolytes.
In this experiment you will test the conductivity of some solids and solutions,
and relate your results to the bond types of the samples tested.
Time required
45 minutes
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4.08–2 • EXPLORING PATTERNS IN CHEMISTRY
CHEMISTRY EXPERIMENTS ON FILETM
Materials
conductivity apparatus (3 pieces of
insulated copper wire, 6V flashlight
bulb, socket for bulb, 6V DC
lantern battery)
aluminum foil
Mylar® (from helium balloon)
soapless steel wool
glass rod
wooden stick
paper clip
charcoal stick
graphite pencil “lead”
plastic ruler
small piece of rubber tubing
small piece of stripped copper wire
1 tbls table salt
1 tbls baking soda
1 tbls granulated sugar
1 liter water
small saucepan
stove or hotplate
Safety note
Take care when heating and testing solutions.
Procedure
Part A: Metallic and covalent bonds
1. Set up the conductivity apparatus as shown in the diagram below.
2. Test the conductivity of the solid substances listed in data table A on the next
page. To do this, touch both wires of your testing device to each sample. If the
bulb lights up, the sample is a conductor. Write “yes” or “no” in the column
labelled “Does it conduct?”
3. When you have tested all the substances, go over your results and write
whether each substance exhibits the properties of a metal or a non-metal.
Write down what bond type you think each has.
battery in holder
light bulb
6V DC
battery
sample
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connecting
wire
crocodile clip
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or transmittal is copyright protected by the publisher.
CHEMISTRY EXPERIMENTS ON FILETM
EXPLORING PATTERNS IN CHEMISTRY • 4.08–3
DATA
Substance
(elements it is
composed of)
TABLE
A
Does it conduct?
Exhibits
properties
of metal or
non-metal?
Bond type
(metallic or
covalent)
glass rod (silicon, oxygen)
aluminum foil
steel wool
Mylar® (a polyester – carbon,
oxygen, hydrogen)
paper clip (nickel, iron)
plastic ruler (polypropylene –
carbon, hydrogen)
rubber tubing (butadiene –
carbon, hydrogen)
copper wire
charcoal stick (carbon)
wooden stick (cellulose)
graphite pencil ‘lead’ (carbon)
Part B: Electrolytes and non-electrolytes
1. Set up the conductivity apparatus as in part A.
2. For each of the substances listed in data table B, test a solid sample for
conductivity and note the results.
3. Put 1 tablespoon of sugar into about 250 ml of water in a small saucepan.
Bring the solution to the boil, stirring to be sure the sugar is dissolved.
4. Test the solution for conductivity and note the results in data table B.
5. Repeat stages 3 and 4 for the samples of table salt and baking soda.
6. Based on your results, decide whether each of these compounds is an
electrolyte or a non-electrolyte and if it contains ionic or covalent bonds.
DATA
Substance
(what is it
composed of)
Conduct
as solid?
TABLE
Conductivity
in solution
B
Electrolyte or
non-electrlyte
Bond type
sugar (dextrose –
carbon, hydrogen,
oxygen)
salt (sodium
chloride)
baking soda
(sodium
hydrogencarbonate)
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4.08–4 • EXPLORING PATTERNS IN CHEMISTRY
CHEMISTRY EXPERIMENTS ON FILETM
Analysis
1. Which of the solids in part A were good conductors? Which were poor
conductors? Which of the samples exhibited metallic properties?
2. Which bond type did the most of the samples with metallic properties have?
3. Can you explain the results for carbon?
4. The wires of your conductivity device are copper coated with rubber. Explain
the role of the copper and the rubber in your device.
5. Did any of the solid substances in part B conduct electricity? If yes, why? If
not, why not?
6. Which of the solutions in part B conduct electricity? Explain why.
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Published by Facts On File, Inc. All electronic storage, reproduction,
or transmittal is copyright protected by the publisher.
4.08 What Makes A Good Conductor?
1. The aluminum foil, steel wool, paper clip, copper, charcoal stick, and graphite pencil were
good conductors and displayed metallic properties. The glass rod, Mylar®, plastic, rubber, and
wood were poor conductors.
2. Most of the samples with metallic properties contained metallic bonds. The exception was carbon.
3. Carbon is a non-metal and therefore has covalent bonds. However, in this experiment it exhibited metallic properties. Carbon in the form of graphite is the only non-metallic element that
conducts electricity. This can be explained by looking at its structure (see diagram below):
strong carbon bonds
weaker bond
between layers
carbon atom
As you can see, graphite is composed of sheets of hexagons of carbon atoms joined by covalent
bonds. Between each sheet, there are weaker (pi) bonds along which the electrons are free to
move. It is the movement of electrons between the layers that explains this unusual property of
graphite.
4. Copper contains metallic bonds and so conducts electricity. Rubber contains covalent bonds
and so does not conduct electricity. It protects the user from getting an electric shock.
5. None of the solids in part B conducted electricity because none contained charged particles
that were free to move. Although salt and baking soda contain ions, these ions were locked in
position within the ionic lattice and could not move freely.
6. Solutions of salt and of baking soda conducted electricity. They are electrolytes. Both compounds contain ionic bonds. Sugar contains covalent bonds (it is composed entirely of nonmetals) and so did not conduct electricity even when dissolved in water. It is a non-electrolyte.