AP Chemistry Unit 3

What are intermolecular forces (IMFs)?

Forces of attraction or repulsion between molecules, weaker than intramolecular bonds (covalent, ionic, or metallic bonds).

List the main types of intermolecular forces in order of strength.

1. Ionic Forces (Strongest)

2. Hydrogen bonding

3. Dipole-dipole interactions

4. London dispersion forces (weakest).

What causes London dispersion forces?

Temporary fluctuations in the electron cloud, creating temporary dipoles that induce attractions between nonpolar molecules.

What molecules exhibit dipole-dipole interactions?

Molecules with permanent dipoles due to differences in electronegativity between atoms (polar molecules).

What is hydrogen bonding?

A strong dipole-dipole interaction that occurs when hydrogen is covalently bonded to highly electronegative atoms (F, O, or N).

How do intermolecular forces affect boiling points?

Stronger IMFs result in higher boiling points because more energy is needed to separate molecules.

Why do polar substances mix with polar solvents?

"Like dissolves like" – polar substances experience similar IMFs with polar solvents, allowing them to mix.

What is polarizability?

The ability of an electron cloud to be distorted, increasing with larger or more spread-out electron clouds.

Why do larger molecules typically have stronger London dispersion forces?

Larger molecules have more electrons, making their electron clouds more polarizable and leading to stronger temporary dipoles.

How does molecular shape influence IMFs?

Molecules with larger surface areas or shapes that allow for closer contact exhibit stronger London dispersion forces.

Why does water have a high boiling point compared to other molecules of similar size?

Strong hydrogen bonding between water molecules requires more energy to break.

What type of IMF is present in all molecules, regardless of polarity?

London dispersion forces.

What is a dipole moment?

A measure of the separation of positive and negative charges in a polar molecule.

Explain the relationship between IMFs and vapor pressure.

Stronger IMFs result in lower vapor pressure because fewer molecules can escape to the gas phase.