Lab: Bond … Which Bond?
Introduction: Ionic bonds are very different than covalent bonds. Because of this, the
substances which are composed of ionic bonds are different than substances which have
covalent bonds. Ionic bonds are quite polar. This means that one end of the bond has a
negative charge, and the other end has a positive charge.
For example: consider NaCl: The Na loses an electron to the Cl. This makes the Na+
positively charged and the Cl- negatively charged. This also means that intermolecular bonds
(bonds between molecules of NaCl) will be fairly strong with an ionic compound. These
strong bonds between molecules mean that the substance likes to “stick together’, that is, it
takes energy to separate them. This means that they tend to have a high melting point, and
are therefore solids at room temperature.
Covalent bonds are less polar or even completely non-polar (for example O2). In O2, each O
atom has an equal pull on the electrons, so neither end of the bond is negatively charged.
This results in weak intermolecular bonds, and therefore molecules which are not strongly
attracted to one another. This results in a low melting point so most of these substances are
gases at room temperature. Larger covalent molecules can be solids, as there are other forces
of attraction between the many atoms.
Purpose: Can the properties of ionic and covalent substances be used to determine which type of bond is in
an unknown substance?
Hypothesis:
Materials:
Safety: Wear safety glasses when using a Bunsen burner or handling chemicals.
Do not allow any of the substances to burn when melting! Start high and bring low.
Procedure: (Refer to board).
Observations: (Make a chart like the one on the overhead).
Conclusion:
Discussion/Questions:
1. Why does an ionic molecule conduct electricity while a covalent molecule does not? (Diagram?)
2. Imagine you are a chemist a couple hundreds of years ago. What evidence is there in this experiment that
suggests that there might be two different types of bonds?
Observation Chart for Bond… Which Bond?
Property
I
Sodium
chloride
(NaCl)
O N I
Potassium
iodide
(KI)
C
Potassium
Chloride
(KCl)
C O V A L E N T
Sucrose
Glucose
Unkn.
(C12H22O11)
(C6H12O6) 1
Melting point
(low/high)
?
Odour
(none/slight/strong)
?
Hardness
(harder / softer)
?
Conductivity
(Yes / No / Slight)
?
Is the unknown substance likely an ionic or a covalent compound?
http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html