Unit Overview

Intermolecular Forces and Properties Overview

AP Chemistry· 5 min read 📊 18-22% of overall AP Chemistry exam score

1. Unit at a Glance

This unit is organized to build from foundational classification of states of matter, to the intermolecular forces that hold matter together, to behavior of gases, then to properties of mixtures and solutions. We move from observable macroscopic properties to the particulate-level explanations that the AP Chemistry exam heavily emphasizes.

Intermolecular forces are the unifying theme of this unit: every physical property we study (boiling point, solubility, pressure, viscosity) traces back to the strength and type of interactions between particles.

Below are all sub-topics covered in this unit:

AP Chemistry Deviation from ideal gas law

Learn why real gases diverge from ideal behavior and what factors cause deviations

★★★⏱ 8 min

AP Chemistry Ideal gas law

Master calculations for pressure, volume, temperature, and moles using the ideal gas law

★★⏱ 7 min

AP Chemistry Intermolecular forces

Identify and compare intermolecular force types and relate their strength to bulk properties

★★★⏱ 10 min

AP Chemistry Kinetic molecular theory

Use kinetic molecular theory to explain gas behavior and temperature relationships

★★★⏱ 8 min

AP Chemistry Mixtures and solutions on the particulate scale

Explore how solute-solvent interactions at the particulate level determine solubility

★★★★⏱ 9 min

AP Chemistry Representations of solutions

Interpret and draw particulate and macroscopic representations of solutions

★★⏱ 6 min

AP Chemistry Solids, liquids, and gases

Compare the structural and physical properties of the three main states of matter

★⏱ 5 min

AP Chemistry Solutions and mixtures

Calculate concentration, solubility, and colligative properties for solutions

★★★★⏱ 10 min

2. Common Pitfalls

Wrong move:

Confusing intermolecular forces with intramolecular bonds

Why:

Intermolecular forces act between separate molecules, while intramolecular bonds hold atoms together within a molecule. This is a common AP exam trap.

Correct move:

Always check if the question refers to interactions between molecules or bonds within a molecule when comparing force strength

Wrong move:

Assuming ideal gas law applies to all gases under all conditions

Why:

Ideal gas law assumes no intermolecular forces and zero molecular volume, which is only true at low pressure and high temperature

Correct move:

Remember that deviations from ideal behavior are largest at high pressure and low temperature

Wrong move:

Ignoring intermolecular forces when predicting solubility

Why:

The 'like dissolves like' rule is rooted in intermolecular interactions between solute and solvent

Correct move:

Always compare the polarity and intermolecular force types of solute and solvent to predict solubility

3. Quick Reference Cheatsheet

Concept / Formula	Description
$P V = n R T$	Ideal gas law: $P$ = pressure, $V$ = volume, $n$ = moles, $R$ = gas constant, $T$ = absolute temperature
London Dispersion Forces	Weak intermolecular forces present in all molecules; strength increases with molar mass and surface area
Hydrogen Bonding	Strong dipole-dipole interaction between H bonded to N/O/F and a lone pair on N/O/F in another molecule
KMT Postulates	Ideal gases have no intermolecular forces, zero molecular volume, and random elastic collisions
$M = \frac{m o l so l u t e}{L so l u t i o n}$	Molarity, the standard concentration unit for solutions in AP Chemistry
$\frac{P _{1} V _{1}}{n _{1} T _{1}} = \frac{P _{2} V _{2}}{n _{2} T _{2}}$	Combined gas law for ideal gases under changing conditions
'Like dissolves like'	Solubility rule: polar solutes dissolve in polar solvents, nonpolar in nonpolar solvents
Intermolecular vs Intramolecular	Intermolecular (between molecules) are weaker than intramolecular (covalent/ionic bonds within molecules)

What's Next

Begin your study of this unit with the first sub-topic to build your foundation of states of matter. Once you complete all sub-topics in Unit 3, you will be ready to move on to the next unit covering chemical reactions, where your knowledge of solutions and concentration will be applied extensively.