ABSTRACT
Intermolecular forces Often, macroscopic observations made with one’s senses are rooted in the types and strengths of attractions/repulsions between chemical species on a molecular scale. For example, your eyes tell you that waxing a car causes water to form large droplets called beads, but how does it do this, and how does wax protect a car body from rusting? Why do soaps foam and why are there soaps and specialty automotive detergents for your car? Why are there different “weights” for motor oil and why does your car require a particular one? All of these questions are related to intermolecular (IM) forces, or the forces that develop between molecules in vapors, liquids, and at solid surfaces. It is important to distinguish in your mind the difference between bonding interactions, which occur within a molecule, and the forces between molecules. For an individual atom and for chemical reactions, the bonding forces within molecules are important. It is the energy stored in chemical bonds that make hydrocarbons like octane excellent fuels for your engine. For understanding large collections of molecules that we can see, hold, and touch, intermolecular forces become more important. For example, the very strong intermolecular forces between H2O molecules in water are the reason behind the anomalously high boiling point for this small molecule. In this chapter, we will introduce the types of intermolecular forces and how they manifest in the chemistry of your car.
