Module 2 Intro

Module 2—Chemical Compounds

Lesson Summary

In this lesson you focused on the following essential questions:

• What are intermolecular forces?
   

• Are the differences between the melting and boiling points of similar substances explained by differences in their intermolecular forces?
  
  

• How does scientific knowledge and theory develop through hypothesis, evidence collection, investigation, and explanation?

Throughout your work in this lesson, you focused on boiling points and empirical data, and you developed a conceptual understanding of how intermolecular bonding forces could be responsible for the phenomena observed.

The melting and boiling points of a substance are related to the strength of intermolecular forces between the molecules of that substance. Higher melting and boiling points indicate stronger intermolecular forces. With an increase in the overall size of the molecule, there is an associated increase in the number of electrons. This increase, too, will increase the strength of intermolecular bonds and lead to higher melting points and boiling points.

You also examined some of the physical properties of liquids, focusing on solubility, surface tension, cohesion and adhesion, volatility, and density and how these could be explained by the intermolecular forces you learned about in this lesson.

Lesson Glossary

intermolecular force: the relatively weak forces of attraction and repulsion between molecules

intramolecular force: the relatively strong bonds or forces of attraction and repulsion within a molecule; typically covalent bonds

momentary dipole: an uneven distribution of electrons around a molecule, resulting in a temporary charge difference between its ends