In this lesson we explored the various kinds of bonds that determine the physical properties of materials and we learned how to tell from its chemical formula which bonds were present in any given material. 

We saw that in network materials the bonds that hold the atoms together are the same ones that determine the  material's physical properties - covalent bonds between non-metal atoms, ionic bonds between metal and non-metal atoms, or metallic bonds between metal atoms.  We also learned that these are all relatively strong bonds, giving these materials very high melting and boiling points.

We found that for molecular materials, however, the covalent bonds holding the atoms together within molecules (called "interatomic" or "intramolecular" bonds) are different from the bonds between molecules (the "intermolecular" bonds) that determine the material's physical properties.   These intermolecular bonds - Van der Waal's bonds, dipole-dipole bonds, and hydrogen bonds, are far weaker than interatomic bonds so that molecular materials have far lower melting and boiling points than network materials.

We learned to use a molecule's Lewis structure to determine its shape, and, from its shape and composition, to predict its polarity, which, in turn helped us determine the kinds of intermolecular bonds that were present.  These, in turn, allowed us to make reasonable predictions about the physical properties of molecular materials: that water (H₂O), for example, should have a higher boiling point than methyl chloride (CH₃Cl); or that methyl alcohol (CH₃OH) should dissolve in water but methane (CH₄) should not.

Review the objectives to make sure that you have covered everything that you should have for this lesson, then test yourself by taking the self-quiz.

There is no problem set for this lesson, but do remember to complete and turn in the lab exercise before you go on.

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E-mail instructor: Eden Francis

Clackamas Community College
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