SNC2D
Name:
PHYSICAL PROPERTIES OF IONIC AND MOLECULAR SOLIDS
Certain compounds are made of molecules in which their atoms are held together by covalent
bonds. These compounds are called molecular solids because they are made of molecules as
opposed to ions. Other compounds are made up of a network of negative anions and positive
cations, arranged in such a way that each positive ion is surrounded exclusively by negative
ions and vice-versa. The solid is held together due to the attraction between the positive and
negative charges, thus forming a crystal lattice. These solids are called ionic compounds.
Purpose
To examine the physical properties molecular and ionic solids.
Questions
How does the type of chemical bonding (ionic / molecular) affect:
1. melting point?
2. solubility in water?
3. electrical conductivity as a solid?
4. electrical conductivity in aqueous solution?
Hypothesis
Create an “If… then …” statement to predict one of the above questions. Each pod of 4
students will answer all of the questions; you will be responsible for one.
If the solid is ionic, then its _______________ will be (higher than / lower than / the same as) a
molecular solid. The rationale for this hypothesis is __________________________________
___________________________________________________________________________
Materials
 safety goggles
 2 small beakers
 glass stirring rod
 scoopula
 beaker tongs
 tea light
 conductivity tester





distilled water
Epsom Salts (MgSO4)
rock salt, NaCl(s)
flour, C6H10O5(s)
sucrose, C12H22O11(s)
Apparatus
Draw a proper scientific diagram of the equipment and materials used in your investigation.
SNC2D
Name:
Procedure
Design your own procedure to test your variable and get it approved by the teacher before
commencing your investigation. Be clear and specific. Consider safety and waste
disposal/clean up.
Observations
Epsom Salt
(MgSO4)
Rock Salt
(NaCl(s))
Flour
(C6H10O5(s))
Sucrose
(C12H22O11(s))
Type of solid (ionic / molecular)
Physical properties
(appearance/ colour / texture /
hardness)
Odour (strong / weak / none)
Melting point (high / low)
Solubility in water (very soluble /
slightly soluble / insoluble)
Conductivity of solid (good /
poor)
Conductivity of solution (good /
poor)
Analysis Questions
1. Which solid had the strongest odour? What does this tell you about the forces holding
the particles of the solid together? (Hint: What is odour? How does odour reach our
noses?)
2. According to your observations regarding melting points, in which solid are the
molecules held more tightly together? Explain with reference to the particle theory of
matter.
3. Which compound was a better conductor as a solid? Using your knowledge of chemical
bonds and/or additional research, support your answer.
4. Which compound was a better conductor as a solution? Using your knowledge of
chemical bonds and/or additional research, support your answer.
5. Predict the results of the tests your group performed for iron (III) sulphate, Fe2(SO4)3(s).
Justify your predictions.
Discussion
Discuss the sources of error in your experiment. What could you have changed to make your
investigation work better?