Strength of Intermolecular Forces

This chapter in the textbook is quite long, but not all of it is well-suited to posts like these. A lot of this reviews concepts from general chemistry and has lots of pretty pictures and I don't want to spend too much time on things like melting point and solubility and soap. The soap thing is something I originally learned in high school and got to see repeated in two general chemistry classes in college and organic chemistry too. I might do a post on it, but for me, it's gotten kind of old. There is some really great material here. I especially like the explanations of biomolecules, but perhaps that's best reserved for later.

In short, I do want to write at least one more post on the odds and ends in the third chapter of my textbook. They will come soon if at all, because I am long overdue on starting the fourth chapter. Before I do either of those things, let's wrap up intermolecular forces.

The strength of intermolecular forces is, in ascending order...

• London Dispersion: caused by fluctuations in charge density across the surfaces of molecules.
• Dipole-Dipole: caused by permanent dipoles.
• Hydrogen Bonding: Caused by extreme loss of electron density on hydrogen when bonded to oxygen or nitrogen (or fluorine, technically).

Note that ion-ion forces, which hold ions together in ionic compounds, could be compared to these forces, although ions are technically not considered molecules. Ion-ion forces are much stronger than any of these intermolecular forces.

Intermolecular forces have the following effects on physical properties...

• Stronger intermolecular forces increase boiling point.
• Stronger intermolecular forces increase melting point.

There's more, but I am skipping it because that's the important stuff and you'd forget the rest anyway. If something I omitted here becomes important later, I'll just blame the problem on you. It's either that or explain the thing when the issue comes up.