Name _________________________
Period _____ Date _______________
THE COMPARISON OF IONIC AND MOLECULAR COMPOUNDS
Activity 1: Comparing the strengths of the forces that hold atoms together in ionic
compounds and molecular compounds.
Data Table 1: This table includes the bond energies of some ionic compounds and
molecular compounds.
Ionic
Bond Energy Molecular Bond Energy
Compound
(KJ/mol)
Compound
(KJ/mol)
KCl
433.0
F–F (F2)
158.78
NaCl
412.1
Cl–F
260.83
KF
489.2
Br–F
280
NaF
659.0
I–F
271.5
Questions:
1. Compare the amount of energy needed to break an ionic bond to the amount of
energy needed to break a covalent bond. Which is stronger? Why do you
suppose this is so?
Activity 2: Comparing the attractive forces between the particles in an ionic compound to
the attractive forces between the particles in a molecular compound.
Gather the following equipment:
Hot plate
2 small test tubes
2 brass test tube holders
Clock
Potassium chlorate, KClO3 (s)
Benzoic acid, C6H5COOH (s)
Procedure:
1. Label the test tubes A and B.
2. Place 0.05 g of the ionic compound KClO3 into test tube A.
3. Place 0.05 g of the molecular compound C6H5COOH into test tube B.
4. Hold both test tubes on the surface of a hot plate. Note the time. Turn the hot
plate on to its highest heat setting.
5. Record the amount of time it takes to melt each compound in Data Table 2.
6. Allow the compounds to cool to room temperature. Add water to the test
tubes to dissolve the compounds, and pour them down the drain with plenty of
running water.
Data Table 2: This table includes the melting time of an ionic compound and the
melting time of a molecular compound.
Compound
Melting Time
(s)
Ionic, KClO3
Molecular, C6H5COOH
Questions
1. Based on the melting times recorded above, which type of compound has stronger
attractive forces between their particles? Remember that you are comparing the
forces that hold K+ ions and ClO3– ions together in the ionic compound, and the
forces that hold C6H5COOH molecules to other C6H5COOH molecules in the
molecular compound.
2. Based on the conclusions drawn in #1, which would have relatively higher
melting and boiling points?
Activity 3: Comparing the hardness of ionic compounds to molecular compounds.
Gather the following equipment:
Mortar & pestle
Calcium carbonate, CaCO3 (s)
Cetyl alcohol, C16H33OH (s)
Procedure:
1. Crush one small piece of the ionic solid (CaCO3) with the mortar & pestle.
Record your observations in Data Table 3.
2. Place the compound in the garbage can. Clean and dry the mortar & pestle.
3. Crush one small piece of the molecular solid (C16H33OH) with the mortar &
pestle. Record your observations in the data table.
4. Place the compound in the garbage can. Clean and dry the mortar & pestle.
Data Table 3: This table includes the results of the test with the mortar & pestle.
Compound
Crushing Results
Ionic, CaCO3
Molecular, C16H33OH
Questions:
1. Describe the hardness of the ionic compound.
2. Describe the hardness of the molecular compound.
3. If you put a diamond in the mortar & pestle, what would you observe?
4. Diamond is a molecular compound, but is classified as a network solid. A
network solid is a compound that combines in a 3D lattice connected with
covalent bonds. In a way, network solids are bonded in an ionic crystal lattice
fashion, but without cations and anions present to cause repulsion during a layer
shift. How does this property make a network solid harder than an ionic
compound?
Activity 4: Comparing the conductivity of ionic compounds to molecular compounds.
Gather the following equipment:
Hot plate
Evaporating dish
Conductivity tester
Potassium chlorate, KClO3 (s)
Sucrose, C12H22O11 (s)
Paraffin wax (candle wax) (s)
Procedure:
1. Place 0.25 g of KClO3 in the evaporating dish. Test its conductivity in the
solid state. Record your observations in Data Table 4. Clean the conductivity
tester.
2. Place the evaporating dish on the hot plate and turn on the hot plate to melt the
KClO3. Test its conductivity in the molten state. Record your observations in
Data Table 4.
3. Clean the evaporating dish and the conductivity tester.
4. Place 10 mL of distilled water in the evaporating dish.
5. Dissolve 0.01 g of KClO3 into the distilled water. Test its conductivity.
Record your observations in Data Table 4.
6. Clean the evaporating dish and the conductivity tester.
7. Repeat steps 1–6 with the other two compounds.
Data Table 4: This table contains the conductivity of several compounds.
Compound
Conductivity
Ionic, KClO3 solid state
Ionic, KClO3 molten state
Ionic, KClO3 aqueous state
Polar molecular, C12H22O11 solid state
Polar molecular, C12H22O11 molten state
Polar molecular, C12H22O11 aqueous state
Nonpolar molecular, paraffin in solid state
Nonpolar molecular, paraffin in molten state
Nonpolar molecular, paraffin in aqueous state
Questions:
1. In what states must an ionic compound be to conduct electricity? Why?
2. What can you conclude about the conductivity of polar molecular substances?
3. What can you conclude about the conductivity of nonpolar molecular substances?
Activity 5: Aqueous solubility of ionic compounds compared to molecular compounds.
Gather the following equipment:
Test tube rack
4 small test tubes
Potassium chlorate, KClO3 (s)
Calcium carbonate, CaCO3 (s)
Benzoic acid, C6H5COOH (s)
Paraffin wax (s)
Distilled water (l)
Procedure:
1. Fill four small test tubes about 2/3 of the way full with distilled water.
2. Place 0.01 g samples of each of the four compounds into the water in each test
tube. Record the aqueous solubility of each compound in Data Table 5.
Data Table 5: This table includes observations from the solubility activity.
Compound
Aqueous Solubility
Ionic, KClO3
Ionic, CaCO3
Polar molecular, C6H5COOH
Nonpolar molecular, Paraffin wax
Questions:
1. The aqueous solubility of ionic compounds depends on their lattice energy, which
is generally the energy needed to break apart an ionic lattice. What conclusion
can be drawn about the aqueous solubility of ionic compounds?
2. What conclusion can be drawn about the aqueous solubility of molecular
compounds?
Be sure to clean all equipment and to return it to its appropriate location.